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INFO-DIR-SECTION Software development
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* Gdb: (gdb).                     The GNU debugger.
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   This file documents the GNU debugger GDB.

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Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
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File: gdb.info,  Node: Stop Reply Packets,  Next: General Query Packets,  Prev: Packets,  Up: Remote Protocol

E.3 Stop Reply Packets
======================

The 'C', 'c', 'S', 's', 'vCont', 'vAttach', 'vRun', 'vStopped', and '?'
packets can receive any of the below as a reply.  Except for '?' and
'vStopped', that reply is only returned when the target halts.  In the
below the exact meaning of "signal number" is defined by the header
'include/gdb/signals.h' in the GDB source code.

   As in the description of request packets, we include spaces in the
reply templates for clarity; these are not part of the reply packet's
syntax.  No GDB stop reply packet uses spaces to separate its
components.

'S AA'
     The program received signal number AA (a two-digit hexadecimal
     number).  This is equivalent to a 'T' response with no N:R pairs.

'T AA N1:R1;N2:R2;...'
     The program received signal number AA (a two-digit hexadecimal
     number).  This is equivalent to an 'S' response, except that the
     'N:R' pairs can carry values of important registers and other
     information directly in the stop reply packet, reducing round-trip
     latency.  Single-step and breakpoint traps are reported this way.
     Each 'N:R' pair is interpreted as follows:

        * If N is a hexadecimal number, it is a register number, and the
          corresponding R gives that register's value.  The data R is a
          series of bytes in target byte order, with each byte given by
          a two-digit hex number.

        * If N is 'thread', then R is the THREAD-ID of the stopped
          thread, as specified in *note thread-id syntax::.

        * If N is 'core', then R is the hexadecimal number of the core
          on which the stop event was detected.

        * If N is a recognized "stop reason", it describes a more
          specific event that stopped the target.  The currently defined
          stop reasons are listed below.  The AA should be '05', the
          trap signal.  At most one stop reason should be present.

        * Otherwise, GDB should ignore this 'N:R' pair and go on to the
          next; this allows us to extend the protocol in the future.

     The currently defined stop reasons are:

     'watch'
     'rwatch'
     'awatch'
          The packet indicates a watchpoint hit, and R is the data
          address, in hex.

     'library'
          The packet indicates that the loaded libraries have changed.
          GDB should use 'qXfer:libraries:read' to fetch a new list of
          loaded libraries.  The R part is ignored.

     'replaylog'
          The packet indicates that the target cannot continue replaying
          logged execution events, because it has reached the end (or
          the beginning when executing backward) of the log.  The value
          of R will be either 'begin' or 'end'.  *Note Reverse
          Execution::, for more information.

'W AA'
'W AA ; process:PID'
     The process exited, and AA is the exit status.  This is only
     applicable to certain targets.

     The second form of the response, including the process ID of the
     exited process, can be used only when GDB has reported support for
     multiprocess protocol extensions; see *note multiprocess
     extensions::.  The PID is formatted as a big-endian hex string.

'X AA'
'X AA ; process:PID'
     The process terminated with signal AA.

     The second form of the response, including the process ID of the
     terminated process, can be used only when GDB has reported support
     for multiprocess protocol extensions; see *note multiprocess
     extensions::.  The PID is formatted as a big-endian hex string.

'O XX...'
     'XX...' is hex encoding of ASCII data, to be written as the
     program's console output.  This can happen at any time while the
     program is running and the debugger should continue to wait for
     'W', 'T', etc.  This reply is not permitted in non-stop mode.

'F CALL-ID,PARAMETER...'
     CALL-ID is the identifier which says which host system call should
     be called.  This is just the name of the function.  Translation
     into the correct system call is only applicable as it's defined in
     GDB.  *Note File-I/O Remote Protocol Extension::, for a list of
     implemented system calls.

     'PARAMETER...' is a list of parameters as defined for this very
     system call.

     The target replies with this packet when it expects GDB to call a
     host system call on behalf of the target.  GDB replies with an
     appropriate 'F' packet and keeps up waiting for the next reply
     packet from the target.  The latest 'C', 'c', 'S' or 's' action is
     expected to be continued.  *Note File-I/O Remote Protocol
     Extension::, for more details.


File: gdb.info,  Node: General Query Packets,  Next: Architecture-Specific Protocol Details,  Prev: Stop Reply Packets,  Up: Remote Protocol

E.4 General Query Packets
=========================

Packets starting with 'q' are "general query packets"; packets starting
with 'Q' are "general set packets".  General query and set packets are a
semi-unified form for retrieving and sending information to and from the
stub.

   The initial letter of a query or set packet is followed by a name
indicating what sort of thing the packet applies to.  For example, GDB
may use a 'qSymbol' packet to exchange symbol definitions with the stub.
These packet names follow some conventions:

   * The name must not contain commas, colons or semicolons.
   * Most GDB query and set packets have a leading upper case letter.
   * The names of custom vendor packets should use a company prefix, in
     lower case, followed by a period.  For example, packets designed at
     the Acme Corporation might begin with 'qacme.foo' (for querying
     foos) or 'Qacme.bar' (for setting bars).

   The name of a query or set packet should be separated from any
parameters by a ':'; the parameters themselves should be separated by
',' or ';'.  Stubs must be careful to match the full packet name, and
check for a separator or the end of the packet, in case two packet names
share a common prefix.  New packets should not begin with 'qC', 'qP', or
'qL'(1).

   Like the descriptions of the other packets, each description here has
a template showing the packet's overall syntax, followed by an
explanation of the packet's meaning.  We include spaces in some of the
templates for clarity; these are not part of the packet's syntax.  No
GDB packet uses spaces to separate its components.

   Here are the currently defined query and set packets:

'QAgent:1'
'QAgent:0'
     Turn on or off the agent as a helper to perform some debugging
     operations delegated from GDB (*note Control Agent::).

'QAllow:OP:VAL...'
     Specify which operations GDB expects to request of the target, as a
     semicolon-separated list of operation name and value pairs.
     Possible values for OP include 'WriteReg', 'WriteMem',
     'InsertBreak', 'InsertTrace', 'InsertFastTrace', and 'Stop'.  VAL
     is either 0, indicating that GDB will not request the operation, or
     1, indicating that it may.  (The target can then use this to set up
     its own internals optimally, for instance if the debugger never
     expects to insert breakpoints, it may not need to install its own
     trap handler.)

'qC'
     Return the current thread ID.

     Reply:
     'QC THREAD-ID'
          Where THREAD-ID is a thread ID as documented in *note
          thread-id syntax::.
     '(anything else)'
          Any other reply implies the old thread ID.

'qCRC:ADDR,LENGTH'
     Compute the CRC checksum of a block of memory using CRC-32 defined
     in IEEE 802.3.  The CRC is computed byte at a time, taking the most
     significant bit of each byte first.  The initial pattern code
     '0xffffffff' is used to ensure leading zeros affect the CRC.

     _Note:_ This is the same CRC used in validating separate debug
     files (*note Debugging Information in Separate Files: Separate
     Debug Files.).  However the algorithm is slightly different.  When
     validating separate debug files, the CRC is computed taking the
     _least_ significant bit of each byte first, and the final result is
     inverted to detect trailing zeros.

     Reply:
     'E NN'
          An error (such as memory fault)
     'C CRC32'
          The specified memory region's checksum is CRC32.

'QDisableRandomization:VALUE'
     Some target operating systems will randomize the virtual address
     space of the inferior process as a security feature, but provide a
     feature to disable such randomization, e.g. to allow for a more
     deterministic debugging experience.  On such systems, this packet
     with a VALUE of 1 directs the target to disable address space
     randomization for processes subsequently started via 'vRun'
     packets, while a packet with a VALUE of 0 tells the target to
     enable address space randomization.

     This packet is only available in extended mode (*note extended
     mode::).

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QDisableRandomization' is not
          supported by the stub.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  This should only be done on targets that actually
     support disabling address space randomization.

'qfThreadInfo'
'qsThreadInfo'
     Obtain a list of all active thread IDs from the target (OS). Since
     there may be too many active threads to fit into one reply packet,
     this query works iteratively: it may require more than one
     query/reply sequence to obtain the entire list of threads.  The
     first query of the sequence will be the 'qfThreadInfo' query;
     subsequent queries in the sequence will be the 'qsThreadInfo'
     query.

     NOTE: This packet replaces the 'qL' query (see below).

     Reply:
     'm THREAD-ID'
          A single thread ID
     'm THREAD-ID,THREAD-ID...'
          a comma-separated list of thread IDs
     'l'
          (lower case letter 'L') denotes end of list.

     In response to each query, the target will reply with a list of one
     or more thread IDs, separated by commas.  GDB will respond to each
     reply with a request for more thread ids (using the 'qs' form of
     the query), until the target responds with 'l' (lower-case ell, for
     "last").  Refer to *note thread-id syntax::, for the format of the
     THREAD-ID fields.

     _Note: GDB will send the 'qfThreadInfo' query during the initial
     connection with the remote target, and the very first thread ID
     mentioned in the reply will be stopped by GDB in a subsequent
     message.  Therefore, the stub should ensure that the first thread
     ID in the 'qfThreadInfo' reply is suitable for being stopped by
     GDB._

'qGetTLSAddr:THREAD-ID,OFFSET,LM'
     Fetch the address associated with thread local storage specified by
     THREAD-ID, OFFSET, and LM.

     THREAD-ID is the thread ID associated with the thread for which to
     fetch the TLS address.  *Note thread-id syntax::.

     OFFSET is the (big endian, hex encoded) offset associated with the
     thread local variable.  (This offset is obtained from the debug
     information associated with the variable.)

     LM is the (big endian, hex encoded) OS/ABI-specific encoding of the
     load module associated with the thread local storage.  For example,
     a GNU/Linux system will pass the link map address of the shared
     object associated with the thread local storage under
     consideration.  Other operating environments may choose to
     represent the load module differently, so the precise meaning of
     this parameter will vary.

     Reply:
     'XX...'
          Hex encoded (big endian) bytes representing the address of the
          thread local storage requested.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'qGetTLSAddr' is not supported
          by the stub.

'qGetTIBAddr:THREAD-ID'
     Fetch address of the Windows OS specific Thread Information Block.

     THREAD-ID is the thread ID associated with the thread.

     Reply:
     'XX...'
          Hex encoded (big endian) bytes representing the linear address
          of the thread information block.

     'E NN'
          An error occured.  This means that either the thread was not
          found, or the address could not be retrieved.

     ''
          An empty reply indicates that 'qGetTIBAddr' is not supported
          by the stub.

'qL STARTFLAG THREADCOUNT NEXTTHREAD'
     Obtain thread information from RTOS. Where: STARTFLAG (one hex
     digit) is one to indicate the first query and zero to indicate a
     subsequent query; THREADCOUNT (two hex digits) is the maximum
     number of threads the response packet can contain; and NEXTTHREAD
     (eight hex digits), for subsequent queries (STARTFLAG is zero), is
     returned in the response as ARGTHREAD.

     Don't use this packet; use the 'qfThreadInfo' query instead (see
     above).

     Reply:
     'qM COUNT DONE ARGTHREAD THREAD...'
          Where: COUNT (two hex digits) is the number of threads being
          returned; DONE (one hex digit) is zero to indicate more
          threads and one indicates no further threads; ARGTHREADID
          (eight hex digits) is NEXTTHREAD from the request packet;
          THREAD... is a sequence of thread IDs, THREADID (eight hex
          digits), from the target.  See
          'remote.c:parse_threadlist_response()'.

'qOffsets'
     Get section offsets that the target used when relocating the
     downloaded image.

     Reply:
     'Text=XXX;Data=YYY[;Bss=ZZZ]'
          Relocate the 'Text' section by XXX from its original address.
          Relocate the 'Data' section by YYY from its original address.
          If the object file format provides segment information (e.g.
          ELF 'PT_LOAD' program headers), GDB will relocate entire
          segments by the supplied offsets.

          _Note: while a 'Bss' offset may be included in the response,
          GDB ignores this and instead applies the 'Data' offset to the
          'Bss' section._

     'TextSeg=XXX[;DataSeg=YYY]'
          Relocate the first segment of the object file, which
          conventionally contains program code, to a starting address of
          XXX.  If 'DataSeg' is specified, relocate the second segment,
          which conventionally contains modifiable data, to a starting
          address of YYY.  GDB will report an error if the object file
          does not contain segment information, or does not contain at
          least as many segments as mentioned in the reply.  Extra
          segments are kept at fixed offsets relative to the last
          relocated segment.

'qP MODE THREAD-ID'
     Returns information on THREAD-ID.  Where: MODE is a hex encoded 32
     bit mode; THREAD-ID is a thread ID (*note thread-id syntax::).

     Don't use this packet; use the 'qThreadExtraInfo' query instead
     (see below).

     Reply: see 'remote.c:remote_unpack_thread_info_response()'.

'QNonStop:1'
'QNonStop:0'
     Enter non-stop ('QNonStop:1') or all-stop ('QNonStop:0') mode.
     *Note Remote Non-Stop::, for more information.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QNonStop' is not supported by
          the stub.

     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).  Use of this packet is controlled by the 'set
     non-stop' command; *note Non-Stop Mode::.

'QPassSignals: SIGNAL [;SIGNAL]...'
     Each listed SIGNAL should be passed directly to the inferior
     process.  Signals are numbered identically to continue packets and
     stop replies (*note Stop Reply Packets::).  Each SIGNAL list item
     should be strictly greater than the previous item.  These signals
     do not need to stop the inferior, or be reported to GDB.  All other
     signals should be reported to GDB.  Multiple 'QPassSignals' packets
     do not combine; any earlier 'QPassSignals' list is completely
     replaced by the new list.  This packet improves performance when
     using 'handle SIGNAL nostop noprint pass'.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QPassSignals' is not supported
          by the stub.

     Use of this packet is controlled by the 'set remote pass-signals'
     command (*note set remote pass-signals: Remote Configuration.).
     This packet is not probed by default; the remote stub must request
     it, by supplying an appropriate 'qSupported' response (*note
     qSupported::).

'QProgramSignals: SIGNAL [;SIGNAL]...'
     Each listed SIGNAL may be delivered to the inferior process.
     Others should be silently discarded.

     In some cases, the remote stub may need to decide whether to
     deliver a signal to the program or not without GDB involvement.
     One example of that is while detaching -- the program's threads may
     have stopped for signals that haven't yet had a chance of being
     reported to GDB, and so the remote stub can use the signal list
     specified by this packet to know whether to deliver or ignore those
     pending signals.

     This does not influence whether to deliver a signal as requested by
     a resumption packet (*note vCont packet::).

     Signals are numbered identically to continue packets and stop
     replies (*note Stop Reply Packets::).  Each SIGNAL list item should
     be strictly greater than the previous item.  Multiple
     'QProgramSignals' packets do not combine; any earlier
     'QProgramSignals' list is completely replaced by the new list.

     Reply:
     'OK'
          The request succeeded.

     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.

     ''
          An empty reply indicates that 'QProgramSignals' is not
          supported by the stub.

     Use of this packet is controlled by the 'set remote
     program-signals' command (*note set remote program-signals: Remote
     Configuration.).  This packet is not probed by default; the remote
     stub must request it, by supplying an appropriate 'qSupported'
     response (*note qSupported::).

'qRcmd,COMMAND'
     COMMAND (hex encoded) is passed to the local interpreter for
     execution.  Invalid commands should be reported using the output
     string.  Before the final result packet, the target may also
     respond with a number of intermediate 'OOUTPUT' console output
     packets.  _Implementors should note that providing access to a
     stubs's interpreter may have security implications_.

     Reply:
     'OK'
          A command response with no output.
     'OUTPUT'
          A command response with the hex encoded output string OUTPUT.
     'E NN'
          Indicate a badly formed request.
     ''
          An empty reply indicates that 'qRcmd' is not recognized.

     (Note that the 'qRcmd' packet's name is separated from the command
     by a ',', not a ':', contrary to the naming conventions above.
     Please don't use this packet as a model for new packets.)

'qSearch:memory:ADDRESS;LENGTH;SEARCH-PATTERN'
     Search LENGTH bytes at ADDRESS for SEARCH-PATTERN.  Both ADDRESS
     and LENGTH are encoded in hex; SEARCH-PATTERN is a sequence of
     bytes, also hex encoded.

     Reply:
     '0'
          The pattern was not found.
     '1,address'
          The pattern was found at ADDRESS.
     'E NN'
          A badly formed request or an error was encountered while
          searching memory.
     ''
          An empty reply indicates that 'qSearch:memory' is not
          recognized.

'QStartNoAckMode'
     Request that the remote stub disable the normal '+'/'-' protocol
     acknowledgments (*note Packet Acknowledgment::).

     Reply:
     'OK'
          The stub has switched to no-acknowledgment mode.  GDB
          acknowledges this reponse, but neither the stub nor GDB shall
          send or expect further '+'/'-' acknowledgments in the current
          connection.
     ''
          An empty reply indicates that the stub does not support
          no-acknowledgment mode.

'qSupported [:GDBFEATURE [;GDBFEATURE]... ]'
     Tell the remote stub about features supported by GDB, and query the
     stub for features it supports.  This packet allows GDB and the
     remote stub to take advantage of each others' features.
     'qSupported' also consolidates multiple feature probes at startup,
     to improve GDB performance--a single larger packet performs better
     than multiple smaller probe packets on high-latency links.  Some
     features may enable behavior which must not be on by default, e.g.
     because it would confuse older clients or stubs.  Other features
     may describe packets which could be automatically probed for, but
     are not.  These features must be reported before GDB will use them.
     This "default unsupported" behavior is not appropriate for all
     packets, but it helps to keep the initial connection time under
     control with new versions of GDB which support increasing numbers
     of packets.

     Reply:
     'STUBFEATURE [;STUBFEATURE]...'
          The stub supports or does not support each returned
          STUBFEATURE, depending on the form of each STUBFEATURE (see
          below for the possible forms).
     ''
          An empty reply indicates that 'qSupported' is not recognized,
          or that no features needed to be reported to GDB.

     The allowed forms for each feature (either a GDBFEATURE in the
     'qSupported' packet, or a STUBFEATURE in the response) are:

     'NAME=VALUE'
          The remote protocol feature NAME is supported, and associated
          with the specified VALUE.  The format of VALUE depends on the
          feature, but it must not include a semicolon.
     'NAME+'
          The remote protocol feature NAME is supported, and does not
          need an associated value.
     'NAME-'
          The remote protocol feature NAME is not supported.
     'NAME?'
          The remote protocol feature NAME may be supported, and GDB
          should auto-detect support in some other way when it is
          needed.  This form will not be used for GDBFEATURE
          notifications, but may be used for STUBFEATURE responses.

     Whenever the stub receives a 'qSupported' request, the supplied set
     of GDB features should override any previous request.  This allows
     GDB to put the stub in a known state, even if the stub had
     previously been communicating with a different version of GDB.

     The following values of GDBFEATURE (for the packet sent by GDB) are
     defined:

     'multiprocess'
          This feature indicates whether GDB supports multiprocess
          extensions to the remote protocol.  GDB does not use such
          extensions unless the stub also reports that it supports them
          by including 'multiprocess+' in its 'qSupported' reply.  *Note
          multiprocess extensions::, for details.

     'xmlRegisters'
          This feature indicates that GDB supports the XML target
          description.  If the stub sees 'xmlRegisters=' with target
          specific strings separated by a comma, it will report register
          description.

     'qRelocInsn'
          This feature indicates whether GDB supports the 'qRelocInsn'
          packet (*note Relocate instruction reply packet: Tracepoint
          Packets.).

     Stubs should ignore any unknown values for GDBFEATURE.  Any GDB
     which sends a 'qSupported' packet supports receiving packets of
     unlimited length (earlier versions of GDB may reject overly long
     responses).  Additional values for GDBFEATURE may be defined in the
     future to let the stub take advantage of new features in GDB, e.g.
     incompatible improvements in the remote protocol--the
     'multiprocess' feature is an example of such a feature.  The stub's
     reply should be independent of the GDBFEATURE entries sent by GDB;
     first GDB describes all the features it supports, and then the stub
     replies with all the features it supports.

     Similarly, GDB will silently ignore unrecognized stub feature
     responses, as long as each response uses one of the standard forms.

     Some features are flags.  A stub which supports a flag feature
     should respond with a '+' form response.  Other features require
     values, and the stub should respond with an '=' form response.

     Each feature has a default value, which GDB will use if
     'qSupported' is not available or if the feature is not mentioned in
     the 'qSupported' response.  The default values are fixed; a stub is
     free to omit any feature responses that match the defaults.

     Not all features can be probed, but for those which can, the
     probing mechanism is useful: in some cases, a stub's internal
     architecture may not allow the protocol layer to know some
     information about the underlying target in advance.  This is
     especially common in stubs which may be configured for multiple
     targets.

     These are the currently defined stub features and their properties:

     Feature Name              Value          Default   Probe
                               Required                 Allowed
                                                        
     'PacketSize'              Yes            '-'       No
                                                        
     'qXfer:auxv:read'         No             '-'       Yes
                                                        
     'qXfer:btrace:read'       No             '-'       Yes
                                                        
     'qXfer:features:read'     No             '-'       Yes
                                                        
     'qXfer:libraries:read'    No             '-'       Yes
                                                        
     'qXfer:libraries-svr4:read'No            '-'       Yes
                                                        
     'augmented-libraries-svr4-read'No        '-'       No
                                                        
     'qXfer:memory-map:read'   No             '-'       Yes
                                                        
     'qXfer:sdata:read'        No             '-'       Yes
                                                        
     'qXfer:spu:read'          No             '-'       Yes
                                                        
     'qXfer:spu:write'         No             '-'       Yes
                                                        
     'qXfer:siginfo:read'      No             '-'       Yes
                                                        
     'qXfer:siginfo:write'     No             '-'       Yes
                                                        
     'qXfer:threads:read'      No             '-'       Yes
                                                        
     'qXfer:traceframe-info:read'No           '-'       Yes
                                                        
     'qXfer:uib:read'          No             '-'       Yes
                                                        
     'qXfer:fdpic:read'        No             '-'       Yes
                                                        
     'Qbtrace:off'             Yes            '-'       Yes
                                                        
     'Qbtrace:bts'             Yes            '-'       Yes
                                                        
     'QNonStop'                No             '-'       Yes
                                                        
     'QPassSignals'            No             '-'       Yes
                                                        
     'QStartNoAckMode'         No             '-'       Yes
                                                        
     'multiprocess'            No             '-'       No
                                                        
     'ConditionalBreakpoints'  No             '-'       No
                                                        
     'ConditionalTracepoints'  No             '-'       No
                                                        
     'ReverseContinue'         No             '-'       No
                                                        
     'ReverseStep'             No             '-'       No
                                                        
     'TracepointSource'        No             '-'       No
                                                        
     'QAgent'                  No             '-'       No
                                                        
     'QAllow'                  No             '-'       No
                                                        
     'QDisableRandomization'   No             '-'       No
                                                        
     'EnableDisableTracepoints'No             '-'       No
                                                        
     'QTBuffer:size'           No             '-'       No
                                                        
     'tracenz'                 No             '-'       No
                                                        
     'BreakpointCommands'      No             '-'       No
                                                        

     These are the currently defined stub features, in more detail:

     'PacketSize=BYTES'
          The remote stub can accept packets up to at least BYTES in
          length.  GDB will send packets up to this size for bulk
          transfers, and will never send larger packets.  This is a
          limit on the data characters in the packet, including the
          frame and checksum.  There is no trailing NUL byte in a remote
          protocol packet; if the stub stores packets in a
          NUL-terminated format, it should allow an extra byte in its
          buffer for the NUL. If this stub feature is not supported, GDB
          guesses based on the size of the 'g' packet response.

     'qXfer:auxv:read'
          The remote stub understands the 'qXfer:auxv:read' packet
          (*note qXfer auxiliary vector read::).

     'qXfer:btrace:read'
          The remote stub understands the 'qXfer:btrace:read' packet
          (*note qXfer btrace read::).

     'qXfer:features:read'
          The remote stub understands the 'qXfer:features:read' packet
          (*note qXfer target description read::).

     'qXfer:libraries:read'
          The remote stub understands the 'qXfer:libraries:read' packet
          (*note qXfer library list read::).

     'qXfer:libraries-svr4:read'
          The remote stub understands the 'qXfer:libraries-svr4:read'
          packet (*note qXfer svr4 library list read::).

     'augmented-libraries-svr4-read'
          The remote stub understands the augmented form of the
          'qXfer:libraries-svr4:read' packet (*note qXfer svr4 library
          list read::).

     'qXfer:memory-map:read'
          The remote stub understands the 'qXfer:memory-map:read' packet
          (*note qXfer memory map read::).

     'qXfer:sdata:read'
          The remote stub understands the 'qXfer:sdata:read' packet
          (*note qXfer sdata read::).

     'qXfer:spu:read'
          The remote stub understands the 'qXfer:spu:read' packet (*note
          qXfer spu read::).

     'qXfer:spu:write'
          The remote stub understands the 'qXfer:spu:write' packet
          (*note qXfer spu write::).

     'qXfer:siginfo:read'
          The remote stub understands the 'qXfer:siginfo:read' packet
          (*note qXfer siginfo read::).

     'qXfer:siginfo:write'
          The remote stub understands the 'qXfer:siginfo:write' packet
          (*note qXfer siginfo write::).

     'qXfer:threads:read'
          The remote stub understands the 'qXfer:threads:read' packet
          (*note qXfer threads read::).

     'qXfer:traceframe-info:read'
          The remote stub understands the 'qXfer:traceframe-info:read'
          packet (*note qXfer traceframe info read::).

     'qXfer:uib:read'
          The remote stub understands the 'qXfer:uib:read' packet (*note
          qXfer unwind info block::).

     'qXfer:fdpic:read'
          The remote stub understands the 'qXfer:fdpic:read' packet
          (*note qXfer fdpic loadmap read::).

     'QNonStop'
          The remote stub understands the 'QNonStop' packet (*note
          QNonStop::).

     'QPassSignals'
          The remote stub understands the 'QPassSignals' packet (*note
          QPassSignals::).

     'QStartNoAckMode'
          The remote stub understands the 'QStartNoAckMode' packet and
          prefers to operate in no-acknowledgment mode.  *Note Packet
          Acknowledgment::.

     'multiprocess'
          The remote stub understands the multiprocess extensions to the
          remote protocol syntax.  The multiprocess extensions affect
          the syntax of thread IDs in both packets and replies (*note
          thread-id syntax::), and add process IDs to the 'D' packet and
          'W' and 'X' replies.  Note that reporting this feature
          indicates support for the syntactic extensions only, not that
          the stub necessarily supports debugging of more than one
          process at a time.  The stub must not use multiprocess
          extensions in packet replies unless GDB has also indicated it
          supports them in its 'qSupported' request.

     'qXfer:osdata:read'
          The remote stub understands the 'qXfer:osdata:read' packet
          ((*note qXfer osdata read::).

     'ConditionalBreakpoints'
          The target accepts and implements evaluation of conditional
          expressions defined for breakpoints.  The target will only
          report breakpoint triggers when such conditions are true
          (*note Break Conditions: Conditions.).

     'ConditionalTracepoints'
          The remote stub accepts and implements conditional expressions
          defined for tracepoints (*note Tracepoint Conditions::).

     'ReverseContinue'
          The remote stub accepts and implements the reverse continue
          packet (*note bc::).

     'ReverseStep'
          The remote stub accepts and implements the reverse step packet
          (*note bs::).

     'TracepointSource'
          The remote stub understands the 'QTDPsrc' packet that supplies
          the source form of tracepoint definitions.

     'QAgent'
          The remote stub understands the 'QAgent' packet.

     'QAllow'
          The remote stub understands the 'QAllow' packet.

     'QDisableRandomization'
          The remote stub understands the 'QDisableRandomization'
          packet.

     'StaticTracepoint'
          The remote stub supports static tracepoints.

     'InstallInTrace'
          The remote stub supports installing tracepoint in tracing.

     'EnableDisableTracepoints'
          The remote stub supports the 'QTEnable' (*note QTEnable::) and
          'QTDisable' (*note QTDisable::) packets that allow tracepoints
          to be enabled and disabled while a trace experiment is
          running.

     'QTBuffer:size'
          The remote stub supports the 'QTBuffer:size' (*note
          QTBuffer-size::) packet that allows to change the size of the
          trace buffer.

     'tracenz'
          The remote stub supports the 'tracenz' bytecode for collecting
          strings.  See *note Bytecode Descriptions:: for details about
          the bytecode.

     'BreakpointCommands'
          The remote stub supports running a breakpoint's command list
          itself, rather than reporting the hit to GDB.

     'Qbtrace:off'
          The remote stub understands the 'Qbtrace:off' packet.

     'Qbtrace:bts'
          The remote stub understands the 'Qbtrace:bts' packet.

'qSymbol::'
     Notify the target that GDB is prepared to serve symbol lookup
     requests.  Accept requests from the target for the values of
     symbols.

     Reply:
     'OK'
          The target does not need to look up any (more) symbols.
     'qSymbol:SYM_NAME'
          The target requests the value of symbol SYM_NAME (hex
          encoded).  GDB may provide the value by using the
          'qSymbol:SYM_VALUE:SYM_NAME' message, described below.

'qSymbol:SYM_VALUE:SYM_NAME'
     Set the value of SYM_NAME to SYM_VALUE.

     SYM_NAME (hex encoded) is the name of a symbol whose value the
     target has previously requested.

     SYM_VALUE (hex) is the value for symbol SYM_NAME.  If GDB cannot
     supply a value for SYM_NAME, then this field will be empty.

     Reply:
     'OK'
          The target does not need to look up any (more) symbols.
     'qSymbol:SYM_NAME'
          The target requests the value of a new symbol SYM_NAME (hex
          encoded).  GDB will continue to supply the values of symbols
          (if available), until the target ceases to request them.

'qTBuffer'
'QTBuffer'
'QTDisconnected'
'QTDP'
'QTDPsrc'
'QTDV'
'qTfP'
'qTfV'
'QTFrame'
'qTMinFTPILen'

     *Note Tracepoint Packets::.

'qThreadExtraInfo,THREAD-ID'
     Obtain from the target OS a printable string description of thread
     attributes for the thread THREAD-ID; see *note thread-id syntax::,
     for the forms of THREAD-ID.  This string may contain anything that
     the target OS thinks is interesting for GDB to tell the user about
     the thread.  The string is displayed in GDB's 'info threads'
     display.  Some examples of possible thread extra info strings are
     'Runnable', or 'Blocked on Mutex'.

     Reply:
     'XX...'
          Where 'XX...' is a hex encoding of ASCII data, comprising the
          printable string containing the extra information about the
          thread's attributes.

     (Note that the 'qThreadExtraInfo' packet's name is separated from
     the command by a ',', not a ':', contrary to the naming conventions
     above.  Please don't use this packet as a model for new packets.)

'QTNotes'
'qTP'
'QTSave'
'qTsP'
'qTsV'
'QTStart'
'QTStop'
'QTEnable'
'QTDisable'
'QTinit'
'QTro'
'qTStatus'
'qTV'
'qTfSTM'
'qTsSTM'
'qTSTMat'
     *Note Tracepoint Packets::.

'qXfer:OBJECT:read:ANNEX:OFFSET,LENGTH'
     Read uninterpreted bytes from the target's special data area
     identified by the keyword OBJECT.  Request LENGTH bytes starting at
     OFFSET bytes into the data.  The content and encoding of ANNEX is
     specific to OBJECT; it can supply additional details about what
     data to access.

     Here are the specific requests of this form defined so far.  All
     'qXfer:OBJECT:read:...' requests use the same reply formats, listed
     below.

     'qXfer:auxv:read::OFFSET,LENGTH'
          Access the target's "auxiliary vector".  *Note auxiliary
          vector: OS Information.  Note ANNEX must be empty.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:btrace:read:ANNEX:OFFSET,LENGTH'

          Return a description of the current branch trace.  *Note
          Branch Trace Format::.  The annex part of the generic 'qXfer'
          packet may have one of the following values:

          'all'
               Returns all available branch trace.

          'new'
               Returns all available branch trace if the branch trace
               changed since the last read request.

          'delta'
               Returns the new branch trace since the last read request.
               Adds a new block to the end of the trace that begins at
               zero and ends at the source location of the first branch
               in the trace buffer.  This extra block is used to stitch
               traces together.

               If the trace buffer overflowed, returns an error
               indicating the overflow.

          This packet is not probed by default; the remote stub must
          request it by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:features:read:ANNEX:OFFSET,LENGTH'
          Access the "target description".  *Note Target Descriptions::.
          The annex specifies which XML document to access.  The main
          description is always loaded from the 'target.xml' annex.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:libraries:read:ANNEX:OFFSET,LENGTH'
          Access the target's list of loaded libraries.  *Note Library
          List Format::.  The annex part of the generic 'qXfer' packet
          must be empty (*note qXfer read::).

          Targets which maintain a list of libraries in the program's
          memory do not need to implement this packet; it is designed
          for platforms where the operating system manages the list of
          loaded libraries.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:libraries-svr4:read:ANNEX:OFFSET,LENGTH'
          Access the target's list of loaded libraries when the target
          is an SVR4 platform.  *Note Library List Format for SVR4
          Targets::.  The annex part of the generic 'qXfer' packet must
          be empty unless the remote stub indicated it supports the
          augmented form of this packet by supplying an appropriate
          'qSupported' response (*note qXfer read::, *note
          qSupported::).

          This packet is optional for better performance on SVR4
          targets.  GDB uses memory read packets to read the SVR4
          library list otherwise.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

          If the remote stub indicates it supports the augmented form of
          this packet then the annex part of the generic 'qXfer' packet
          may contain a semicolon-separated list of 'NAME=VALUE'
          arguments.  The currently supported arguments are:

          'start=ADDRESS'
               A hexadecimal number specifying the address of the
               'struct link_map' to start reading the library list from.
               If unset or zero then the first 'struct link_map' in the
               library list will be chosen as the starting point.

          'prev=ADDRESS'
               A hexadecimal number specifying the address of the
               'struct link_map' immediately preceding the 'struct
               link_map' specified by the 'start' argument.  If unset or
               zero then the remote stub will expect that no 'struct
               link_map' exists prior to the starting point.

          Arguments that are not understood by the remote stub will be
          silently ignored.

     'qXfer:memory-map:read::OFFSET,LENGTH'
          Access the target's "memory-map".  *Note Memory Map Format::.
          The annex part of the generic 'qXfer' packet must be empty
          (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:sdata:read::OFFSET,LENGTH'

          Read contents of the extra collected static tracepoint marker
          information.  The annex part of the generic 'qXfer' packet
          must be empty (*note qXfer read::).  *Note Tracepoint Action
          Lists: Tracepoint Actions.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:siginfo:read::OFFSET,LENGTH'
          Read contents of the extra signal information on the target
          system.  The annex part of the generic 'qXfer' packet must be
          empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:spu:read:ANNEX:OFFSET,LENGTH'
          Read contents of an 'spufs' file on the target system.  The
          annex specifies which file to read; it must be of the form
          'ID/NAME', where ID specifies an SPU context ID in the target
          process, and NAME identifes the 'spufs' file in that context
          to be accessed.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:threads:read::OFFSET,LENGTH'
          Access the list of threads on target.  *Note Thread List
          Format::.  The annex part of the generic 'qXfer' packet must
          be empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:traceframe-info:read::OFFSET,LENGTH'

          Return a description of the current traceframe's contents.
          *Note Traceframe Info Format::.  The annex part of the generic
          'qXfer' packet must be empty (*note qXfer read::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:uib:read:PC:OFFSET,LENGTH'

          Return the unwind information block for PC.  This packet is
          used on OpenVMS/ia64 to ask the kernel unwind information.

          This packet is not probed by default.

     'qXfer:fdpic:read:ANNEX:OFFSET,LENGTH'
          Read contents of 'loadmap's on the target system.  The annex,
          either 'exec' or 'interp', specifies which 'loadmap',
          executable 'loadmap' or interpreter 'loadmap' to read.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:osdata:read::OFFSET,LENGTH'
          Access the target's "operating system information".  *Note
          Operating System Information::.

     Reply:
     'm DATA'
          Data DATA (*note Binary Data::) has been read from the target.
          There may be more data at a higher address (although it is
          permitted to return 'm' even for the last valid block of data,
          as long as at least one byte of data was read).  It is
          possible for DATA to have fewer bytes than the LENGTH in the
          request.

     'l DATA'
          Data DATA (*note Binary Data::) has been read from the target.
          There is no more data to be read.  It is possible for DATA to
          have fewer bytes than the LENGTH in the request.

     'l'
          The OFFSET in the request is at the end of the data.  There is
          no more data to be read.

     'E00'
          The request was malformed, or ANNEX was invalid.

     'E NN'
          The offset was invalid, or there was an error encountered
          reading the data.  The NN part is a hex-encoded 'errno' value.

     ''
          An empty reply indicates the OBJECT string was not recognized
          by the stub, or that the object does not support reading.

'qXfer:OBJECT:write:ANNEX:OFFSET:DATA...'
     Write uninterpreted bytes into the target's special data area
     identified by the keyword OBJECT, starting at OFFSET bytes into the
     data.  The binary-encoded data (*note Binary Data::) to be written
     is given by DATA....  The content and encoding of ANNEX is specific
     to OBJECT; it can supply additional details about what data to
     access.

     Here are the specific requests of this form defined so far.  All
     'qXfer:OBJECT:write:...' requests use the same reply formats,
     listed below.

     'qXfer:siginfo:write::OFFSET:DATA...'
          Write DATA to the extra signal information on the target
          system.  The annex part of the generic 'qXfer' packet must be
          empty (*note qXfer write::).

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     'qXfer:spu:write:ANNEX:OFFSET:DATA...'
          Write DATA to an 'spufs' file on the target system.  The annex
          specifies which file to write; it must be of the form
          'ID/NAME', where ID specifies an SPU context ID in the target
          process, and NAME identifes the 'spufs' file in that context
          to be accessed.

          This packet is not probed by default; the remote stub must
          request it, by supplying an appropriate 'qSupported' response
          (*note qSupported::).

     Reply:
     'NN'
          NN (hex encoded) is the number of bytes written.  This may be
          fewer bytes than supplied in the request.

     'E00'
          The request was malformed, or ANNEX was invalid.

     'E NN'
          The offset was invalid, or there was an error encountered
          writing the data.  The NN part is a hex-encoded 'errno' value.

     ''
          An empty reply indicates the OBJECT string was not recognized
          by the stub, or that the object does not support writing.

'qXfer:OBJECT:OPERATION:...'
     Requests of this form may be added in the future.  When a stub does
     not recognize the OBJECT keyword, or its support for OBJECT does
     not recognize the OPERATION keyword, the stub must respond with an
     empty packet.

'qAttached:PID'
     Return an indication of whether the remote server attached to an
     existing process or created a new process.  When the multiprocess
     protocol extensions are supported (*note multiprocess
     extensions::), PID is an integer in hexadecimal format identifying
     the target process.  Otherwise, GDB will omit the PID field and the
     query packet will be simplified as 'qAttached'.

     This query is used, for example, to know whether the remote process
     should be detached or killed when a GDB session is ended with the
     'quit' command.

     Reply:
     '1'
          The remote server attached to an existing process.
     '0'
          The remote server created a new process.
     'E NN'
          A badly formed request or an error was encountered.

'Qbtrace:bts'
     Enable branch tracing for the current thread using bts tracing.

     Reply:
     'OK'
          Branch tracing has been enabled.
     'E.errtext'
          A badly formed request or an error was encountered.

'Qbtrace:off'
     Disable branch tracing for the current thread.

     Reply:
     'OK'
          Branch tracing has been disabled.
     'E.errtext'
          A badly formed request or an error was encountered.

   ---------- Footnotes ----------

   (1) The 'qP' and 'qL' packets predate these conventions, and have
arguments without any terminator for the packet name; we suspect they
are in widespread use in places that are difficult to upgrade.  The 'qC'
packet has no arguments, but some existing stubs (e.g. RedBoot) are
known to not check for the end of the packet.


File: gdb.info,  Node: Architecture-Specific Protocol Details,  Next: Tracepoint Packets,  Prev: General Query Packets,  Up: Remote Protocol

E.5 Architecture-Specific Protocol Details
==========================================

This section describes how the remote protocol is applied to specific
target architectures.  Also see *note Standard Target Features::, for
details of XML target descriptions for each architecture.

* Menu:

* ARM-Specific Protocol Details::
* MIPS-Specific Protocol Details::


File: gdb.info,  Node: ARM-Specific Protocol Details,  Next: MIPS-Specific Protocol Details,  Up: Architecture-Specific Protocol Details

E.5.1 ARM-specific Protocol Details
-----------------------------------

* Menu:

* ARM Breakpoint Kinds::


File: gdb.info,  Node: ARM Breakpoint Kinds,  Up: ARM-Specific Protocol Details

E.5.1.1 ARM Breakpoint Kinds
............................

These breakpoint kinds are defined for the 'Z0' and 'Z1' packets.

2
     16-bit Thumb mode breakpoint.

3
     32-bit Thumb mode (Thumb-2) breakpoint.

4
     32-bit ARM mode breakpoint.


File: gdb.info,  Node: MIPS-Specific Protocol Details,  Prev: ARM-Specific Protocol Details,  Up: Architecture-Specific Protocol Details

E.5.2 MIPS-specific Protocol Details
------------------------------------

* Menu:

* MIPS Register packet Format::
* MIPS Breakpoint Kinds::


File: gdb.info,  Node: MIPS Register packet Format,  Next: MIPS Breakpoint Kinds,  Up: MIPS-Specific Protocol Details

E.5.2.1 MIPS Register Packet Format
...................................

The following 'g'/'G' packets have previously been defined.  In the
below, some thirty-two bit registers are transferred as sixty-four bits.
Those registers should be zero/sign extended (which?)  to fill the space
allocated.  Register bytes are transferred in target byte order.  The
two nibbles within a register byte are transferred most-significant -
least-significant.

MIPS32
     All registers are transferred as thirty-two bit quantities in the
     order: 32 general-purpose; sr; lo; hi; bad; cause; pc; 32
     floating-point registers; fsr; fir; fp.

MIPS64
     All registers are transferred as sixty-four bit quantities
     (including thirty-two bit registers such as 'sr').  The ordering is
     the same as 'MIPS32'.


File: gdb.info,  Node: MIPS Breakpoint Kinds,  Prev: MIPS Register packet Format,  Up: MIPS-Specific Protocol Details

E.5.2.2 MIPS Breakpoint Kinds
.............................

These breakpoint kinds are defined for the 'Z0' and 'Z1' packets.

2
     16-bit MIPS16 mode breakpoint.

3
     16-bit microMIPS mode breakpoint.

4
     32-bit standard MIPS mode breakpoint.

5
     32-bit microMIPS mode breakpoint.


File: gdb.info,  Node: Tracepoint Packets,  Next: Host I/O Packets,  Prev: Architecture-Specific Protocol Details,  Up: Remote Protocol

E.6 Tracepoint Packets
======================

Here we describe the packets GDB uses to implement tracepoints (*note
Tracepoints::).

'QTDP:N:ADDR:ENA:STEP:PASS[:FFLEN][:XLEN,BYTES][-]'
     Create a new tracepoint, number N, at ADDR.  If ENA is 'E', then
     the tracepoint is enabled; if it is 'D', then the tracepoint is
     disabled.  The STEP gives the tracepoint's step count, and PASS
     gives its pass count.  If an 'F' is present, then the tracepoint is
     to be a fast tracepoint, and the FLEN is the number of bytes that
     the target should copy elsewhere to make room for the tracepoint.
     If an 'X' is present, it introduces a tracepoint condition, which
     consists of a hexadecimal length, followed by a comma and
     hex-encoded bytes, in a manner similar to action encodings as
     described below.  If the trailing '-' is present, further 'QTDP'
     packets will follow to specify this tracepoint's actions.

     Replies:
     'OK'
          The packet was understood and carried out.
     'qRelocInsn'
          *Note Relocate instruction reply packet: Tracepoint Packets.
     ''
          The packet was not recognized.

'QTDP:-N:ADDR:[S]ACTION...[-]'
     Define actions to be taken when a tracepoint is hit.  The N and
     ADDR must be the same as in the initial 'QTDP' packet for this
     tracepoint.  This packet may only be sent immediately after another
     'QTDP' packet that ended with a '-'.  If the trailing '-' is
     present, further 'QTDP' packets will follow, specifying more
     actions for this tracepoint.

     In the series of action packets for a given tracepoint, at most one
     can have an 'S' before its first ACTION.  If such a packet is sent,
     it and the following packets define "while-stepping" actions.  Any
     prior packets define ordinary actions -- that is, those taken when
     the tracepoint is first hit.  If no action packet has an 'S', then
     all the packets in the series specify ordinary tracepoint actions.

     The 'ACTION...' portion of the packet is a series of actions,
     concatenated without separators.  Each action has one of the
     following forms:

     'R MASK'
          Collect the registers whose bits are set in MASK, a
          hexadecimal number whose I'th bit is set if register number I
          should be collected.  (The least significant bit is numbered
          zero.)  Note that MASK may be any number of digits long; it
          may not fit in a 32-bit word.

     'M BASEREG,OFFSET,LEN'
          Collect LEN bytes of memory starting at the address in
          register number BASEREG, plus OFFSET.  If BASEREG is '-1',
          then the range has a fixed address: OFFSET is the address of
          the lowest byte to collect.  The BASEREG, OFFSET, and LEN
          parameters are all unsigned hexadecimal values (the '-1' value
          for BASEREG is a special case).

     'X LEN,EXPR'
          Evaluate EXPR, whose length is LEN, and collect memory as it
          directs.  The agent expression EXPR is as described in *note
          Agent Expressions::.  Each byte of the expression is encoded
          as a two-digit hex number in the packet; LEN is the number of
          bytes in the expression (and thus one-half the number of hex
          digits in the packet).

     Any number of actions may be packed together in a single 'QTDP'
     packet, as long as the packet does not exceed the maximum packet
     length (400 bytes, for many stubs).  There may be only one 'R'
     action per tracepoint, and it must precede any 'M' or 'X' actions.
     Any registers referred to by 'M' and 'X' actions must be collected
     by a preceding 'R' action.  (The "while-stepping" actions are
     treated as if they were attached to a separate tracepoint, as far
     as these restrictions are concerned.)

     Replies:
     'OK'
          The packet was understood and carried out.
     'qRelocInsn'
          *Note Relocate instruction reply packet: Tracepoint Packets.
     ''
          The packet was not recognized.

'QTDPsrc:N:ADDR:TYPE:START:SLEN:BYTES'
     Specify a source string of tracepoint N at address ADDR.  This is
     useful to get accurate reproduction of the tracepoints originally
     downloaded at the beginning of the trace run.  The TYPE is the name
     of the tracepoint part, such as 'cond' for the tracepoint's
     conditional expression (see below for a list of types), while BYTES
     is the string, encoded in hexadecimal.

     START is the offset of the BYTES within the overall source string,
     while SLEN is the total length of the source string.  This is
     intended for handling source strings that are longer than will fit
     in a single packet.

     The available string types are 'at' for the location, 'cond' for
     the conditional, and 'cmd' for an action command.  GDB sends a
     separate packet for each command in the action list, in the same
     order in which the commands are stored in the list.

     The target does not need to do anything with source strings except
     report them back as part of the replies to the 'qTfP'/'qTsP' query
     packets.

     Although this packet is optional, and GDB will only send it if the
     target replies with 'TracepointSource' *Note General Query
     Packets::, it makes both disconnected tracing and trace files much
     easier to use.  Otherwise the user must be careful that the
     tracepoints in effect while looking at trace frames are identical
     to the ones in effect during the trace run; even a small
     discrepancy could cause 'tdump' not to work, or a particular trace
     frame not be found.

'QTDV:N:VALUE'
     Create a new trace state variable, number N, with an initial value
     of VALUE, which is a 64-bit signed integer.  Both N and VALUE are
     encoded as hexadecimal values.  GDB has the option of not using
     this packet for initial values of zero; the target should simply
     create the trace state variables as they are mentioned in
     expressions.

'QTFrame:N'
     Select the N'th tracepoint frame from the buffer, and use the
     register and memory contents recorded there to answer subsequent
     request packets from GDB.

     A successful reply from the stub indicates that the stub has found
     the requested frame.  The response is a series of parts,
     concatenated without separators, describing the frame we selected.
     Each part has one of the following forms:

     'F F'
          The selected frame is number N in the trace frame buffer; F is
          a hexadecimal number.  If F is '-1', then there was no frame
          matching the criteria in the request packet.

     'T T'
          The selected trace frame records a hit of tracepoint number T;
          T is a hexadecimal number.

'QTFrame:pc:ADDR'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame whose PC is ADDR; ADDR is a hexadecimal
     number.

'QTFrame:tdp:T'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame that is a hit of tracepoint T; T is a
     hexadecimal number.

'QTFrame:range:START:END'
     Like 'QTFrame:N', but select the first tracepoint frame after the
     currently selected frame whose PC is between START (inclusive) and
     END (inclusive); START and END are hexadecimal numbers.

'QTFrame:outside:START:END'
     Like 'QTFrame:range:START:END', but select the first frame
     _outside_ the given range of addresses (exclusive).

'qTMinFTPILen'
     This packet requests the minimum length of instruction at which a
     fast tracepoint (*note Set Tracepoints::) may be placed.  For
     instance, on the 32-bit x86 architecture, it is possible to use a
     4-byte jump, but it depends on the target system being able to
     create trampolines in the first 64K of memory, which might or might
     not be possible for that system.  So the reply to this packet will
     be 4 if it is able to arrange for that.

     Replies:

     '0'
          The minimum instruction length is currently unknown.
     'LENGTH'
          The minimum instruction length is LENGTH, where LENGTH is a
          hexadecimal number greater or equal to 1.  A reply of 1 means
          that a fast tracepoint may be placed on any instruction
          regardless of size.
     'E'
          An error has occurred.
     ''
          An empty reply indicates that the request is not supported by
          the stub.

'QTStart'
     Begin the tracepoint experiment.  Begin collecting data from
     tracepoint hits in the trace frame buffer.  This packet supports
     the 'qRelocInsn' reply (*note Relocate instruction reply packet:
     Tracepoint Packets.).

'QTStop'
     End the tracepoint experiment.  Stop collecting trace frames.

'QTEnable:N:ADDR'
     Enable tracepoint N at address ADDR in a started tracepoint
     experiment.  If the tracepoint was previously disabled, then
     collection of data from it will resume.

'QTDisable:N:ADDR'
     Disable tracepoint N at address ADDR in a started tracepoint
     experiment.  No more data will be collected from the tracepoint
     unless 'QTEnable:N:ADDR' is subsequently issued.

'QTinit'
     Clear the table of tracepoints, and empty the trace frame buffer.

'QTro:START1,END1:START2,END2:...'
     Establish the given ranges of memory as "transparent".  The stub
     will answer requests for these ranges from memory's current
     contents, if they were not collected as part of the tracepoint hit.

     GDB uses this to mark read-only regions of memory, like those
     containing program code.  Since these areas never change, they
     should still have the same contents they did when the tracepoint
     was hit, so there's no reason for the stub to refuse to provide
     their contents.

'QTDisconnected:VALUE'
     Set the choice to what to do with the tracing run when GDB
     disconnects from the target.  A VALUE of 1 directs the target to
     continue the tracing run, while 0 tells the target to stop tracing
     if GDB is no longer in the picture.

'qTStatus'
     Ask the stub if there is a trace experiment running right now.

     The reply has the form:

     'TRUNNING[;FIELD]...'
          RUNNING is a single digit '1' if the trace is presently
          running, or '0' if not.  It is followed by semicolon-separated
          optional fields that an agent may use to report additional
          status.

     If the trace is not running, the agent may report any of several
     explanations as one of the optional fields:

     'tnotrun:0'
          No trace has been run yet.

     'tstop[:TEXT]:0'
          The trace was stopped by a user-originated stop command.  The
          optional TEXT field is a user-supplied string supplied as part
          of the stop command (for instance, an explanation of why the
          trace was stopped manually).  It is hex-encoded.

     'tfull:0'
          The trace stopped because the trace buffer filled up.

     'tdisconnected:0'
          The trace stopped because GDB disconnected from the target.

     'tpasscount:TPNUM'
          The trace stopped because tracepoint TPNUM exceeded its pass
          count.

     'terror:TEXT:TPNUM'
          The trace stopped because tracepoint TPNUM had an error.  The
          string TEXT is available to describe the nature of the error
          (for instance, a divide by zero in the condition expression);
          it is hex encoded.

     'tunknown:0'
          The trace stopped for some other reason.

     Additional optional fields supply statistical and other
     information.  Although not required, they are extremely useful for
     users monitoring the progress of a trace run.  If a trace has
     stopped, and these numbers are reported, they must reflect the
     state of the just-stopped trace.

     'tframes:N'
          The number of trace frames in the buffer.

     'tcreated:N'
          The total number of trace frames created during the run.  This
          may be larger than the trace frame count, if the buffer is
          circular.

     'tsize:N'
          The total size of the trace buffer, in bytes.

     'tfree:N'
          The number of bytes still unused in the buffer.

     'circular:N'
          The value of the circular trace buffer flag.  '1' means that
          the trace buffer is circular and old trace frames will be
          discarded if necessary to make room, '0' means that the trace
          buffer is linear and may fill up.

     'disconn:N'
          The value of the disconnected tracing flag.  '1' means that
          tracing will continue after GDB disconnects, '0' means that
          the trace run will stop.

'qTP:TP:ADDR'
     Ask the stub for the current state of tracepoint number TP at
     address ADDR.

     Replies:
     'VHITS:USAGE'
          The tracepoint has been hit HITS times so far during the trace
          run, and accounts for USAGE in the trace buffer.  Note that
          'while-stepping' steps are not counted as separate hits, but
          the steps' space consumption is added into the usage number.

'qTV:VAR'
     Ask the stub for the value of the trace state variable number VAR.

     Replies:
     'VVALUE'
          The value of the variable is VALUE.  This will be the current
          value of the variable if the user is examining a running
          target, or a saved value if the variable was collected in the
          trace frame that the user is looking at.  Note that multiple
          requests may result in different reply values, such as when
          requesting values while the program is running.

     'U'
          The value of the variable is unknown.  This would occur, for
          example, if the user is examining a trace frame in which the
          requested variable was not collected.

'qTfP'
'qTsP'
     These packets request data about tracepoints that are being used by
     the target.  GDB sends 'qTfP' to get the first piece of data, and
     multiple 'qTsP' to get additional pieces.  Replies to these packets
     generally take the form of the 'QTDP' packets that define
     tracepoints.  (FIXME add detailed syntax)

'qTfV'
'qTsV'
     These packets request data about trace state variables that are on
     the target.  GDB sends 'qTfV' to get the first vari of data, and
     multiple 'qTsV' to get additional variables.  Replies to these
     packets follow the syntax of the 'QTDV' packets that define trace
     state variables.

'qTfSTM'
'qTsSTM'
     These packets request data about static tracepoint markers that
     exist in the target program.  GDB sends 'qTfSTM' to get the first
     piece of data, and multiple 'qTsSTM' to get additional pieces.
     Replies to these packets take the following form:

     Reply:
     'm ADDRESS:ID:EXTRA'
          A single marker
     'm ADDRESS:ID:EXTRA,ADDRESS:ID:EXTRA...'
          a comma-separated list of markers
     'l'
          (lower case letter 'L') denotes end of list.
     'E NN'
          An error occurred.  The error number NN is given as hex
          digits.
     ''
          An empty reply indicates that the request is not supported by
          the stub.

     The ADDRESS is encoded in hex; ID and EXTRA are strings encoded in
     hex.

     In response to each query, the target will reply with a list of one
     or more markers, separated by commas.  GDB will respond to each
     reply with a request for more markers (using the 'qs' form of the
     query), until the target responds with 'l' (lower-case ell, for
     "last").

'qTSTMat:ADDRESS'
     This packets requests data about static tracepoint markers in the
     target program at ADDRESS.  Replies to this packet follow the
     syntax of the 'qTfSTM' and 'qTsSTM' packets that list static
     tracepoint markers.

'QTSave:FILENAME'
     This packet directs the target to save trace data to the file name
     FILENAME in the target's filesystem.  The FILENAME is encoded as a
     hex string; the interpretation of the file name (relative vs
     absolute, wild cards, etc) is up to the target.

'qTBuffer:OFFSET,LEN'
     Return up to LEN bytes of the current contents of trace buffer,
     starting at OFFSET.  The trace buffer is treated as if it were a
     contiguous collection of traceframes, as per the trace file format.
     The reply consists as many hex-encoded bytes as the target can
     deliver in a packet; it is not an error to return fewer than were
     asked for.  A reply consisting of just 'l' indicates that no bytes
     are available.

'QTBuffer:circular:VALUE'
     This packet directs the target to use a circular trace buffer if
     VALUE is 1, or a linear buffer if the value is 0.

'QTBuffer:size:SIZE'
     This packet directs the target to make the trace buffer be of size
     SIZE if possible.  A value of '-1' tells the target to use whatever
     size it prefers.

'QTNotes:[TYPE:TEXT][;TYPE:TEXT]...'
     This packet adds optional textual notes to the trace run.
     Allowable types include 'user', 'notes', and 'tstop', the TEXT
     fields are arbitrary strings, hex-encoded.

E.6.1 Relocate instruction reply packet
---------------------------------------

When installing fast tracepoints in memory, the target may need to
relocate the instruction currently at the tracepoint address to a
different address in memory.  For most instructions, a simple copy is
enough, but, for example, call instructions that implicitly push the
return address on the stack, and relative branches or other PC-relative
instructions require offset adjustment, so that the effect of executing
the instruction at a different address is the same as if it had executed
in the original location.

   In response to several of the tracepoint packets, the target may also
respond with a number of intermediate 'qRelocInsn' request packets
before the final result packet, to have GDB handle this relocation
operation.  If a packet supports this mechanism, its documentation will
explicitly say so.  See for example the above descriptions for the
'QTStart' and 'QTDP' packets.  The format of the request is:

'qRelocInsn:FROM;TO'

     This requests GDB to copy instruction at address FROM to address
     TO, possibly adjusted so that executing the instruction at TO has
     the same effect as executing it at FROM.  GDB writes the adjusted
     instruction to target memory starting at TO.

   Replies:
'qRelocInsn:ADJUSTED_SIZE'
     Informs the stub the relocation is complete.  The ADJUSTED_SIZE is
     the length in bytes of resulting relocated instruction sequence.
'E NN'
     A badly formed request was detected, or an error was encountered
     while relocating the instruction.


File: gdb.info,  Node: Host I/O Packets,  Next: Interrupts,  Prev: Tracepoint Packets,  Up: Remote Protocol

E.7 Host I/O Packets
====================

The "Host I/O" packets allow GDB to perform I/O operations on the far
side of a remote link.  For example, Host I/O is used to upload and
download files to a remote target with its own filesystem.  Host I/O
uses the same constant values and data structure layout as the
target-initiated File-I/O protocol.  However, the Host I/O packets are
structured differently.  The target-initiated protocol relies on target
memory to store parameters and buffers.  Host I/O requests are initiated
by GDB, and the target's memory is not involved.  *Note File-I/O Remote
Protocol Extension::, for more details on the target-initiated protocol.

   The Host I/O request packets all encode a single operation along with
its arguments.  They have this format:

'vFile:OPERATION: PARAMETER...'
     OPERATION is the name of the particular request; the target should
     compare the entire packet name up to the second colon when checking
     for a supported operation.  The format of PARAMETER depends on the
     operation.  Numbers are always passed in hexadecimal.  Negative
     numbers have an explicit minus sign (i.e. two's complement is not
     used).  Strings (e.g. filenames) are encoded as a series of
     hexadecimal bytes.  The last argument to a system call may be a
     buffer of escaped binary data (*note Binary Data::).

   The valid responses to Host I/O packets are:

'F RESULT [, ERRNO] [; ATTACHMENT]'
     RESULT is the integer value returned by this operation, usually
     non-negative for success and -1 for errors.  If an error has
     occured, ERRNO will be included in the result specifying a value
     defined by the File-I/O protocol (*note Errno Values::).  For
     operations which return data, ATTACHMENT supplies the data as a
     binary buffer.  Binary buffers in response packets are escaped in
     the normal way (*note Binary Data::).  See the individual packet
     documentation for the interpretation of RESULT and ATTACHMENT.

''
     An empty response indicates that this operation is not recognized.

   These are the supported Host I/O operations:

'vFile:open: FILENAME, FLAGS, MODE'
     Open a file at FILENAME and return a file descriptor for it, or
     return -1 if an error occurs.  The FILENAME is a string, FLAGS is
     an integer indicating a mask of open flags (*note Open Flags::),
     and MODE is an integer indicating a mask of mode bits to use if the
     file is created (*note mode_t Values::).  *Note open::, for details
     of the open flags and mode values.

'vFile:close: FD'
     Close the open file corresponding to FD and return 0, or -1 if an
     error occurs.

'vFile:pread: FD, COUNT, OFFSET'
     Read data from the open file corresponding to FD.  Up to COUNT
     bytes will be read from the file, starting at OFFSET relative to
     the start of the file.  The target may read fewer bytes; common
     reasons include packet size limits and an end-of-file condition.
     The number of bytes read is returned.  Zero should only be returned
     for a successful read at the end of the file, or if COUNT was zero.

     The data read should be returned as a binary attachment on success.
     If zero bytes were read, the response should include an empty
     binary attachment (i.e. a trailing semicolon).  The return value is
     the number of target bytes read; the binary attachment may be
     longer if some characters were escaped.

'vFile:pwrite: FD, OFFSET, DATA'
     Write DATA (a binary buffer) to the open file corresponding to FD.
     Start the write at OFFSET from the start of the file.  Unlike many
     'write' system calls, there is no separate COUNT argument; the
     length of DATA in the packet is used.  'vFile:write' returns the
     number of bytes written, which may be shorter than the length of
     DATA, or -1 if an error occurred.

'vFile:unlink: FILENAME'
     Delete the file at FILENAME on the target.  Return 0, or -1 if an
     error occurs.  The FILENAME is a string.

'vFile:readlink: FILENAME'
     Read value of symbolic link FILENAME on the target.  Return the
     number of bytes read, or -1 if an error occurs.

     The data read should be returned as a binary attachment on success.
     If zero bytes were read, the response should include an empty
     binary attachment (i.e. a trailing semicolon).  The return value is
     the number of target bytes read; the binary attachment may be
     longer if some characters were escaped.


File: gdb.info,  Node: Interrupts,  Next: Notification Packets,  Prev: Host I/O Packets,  Up: Remote Protocol

E.8 Interrupts
==============

When a program on the remote target is running, GDB may attempt to
interrupt it by sending a 'Ctrl-C', 'BREAK' or a 'BREAK' followed by
'g', control of which is specified via GDB's 'interrupt-sequence'.

   The precise meaning of 'BREAK' is defined by the transport mechanism
and may, in fact, be undefined.  GDB does not currently define a 'BREAK'
mechanism for any of the network interfaces except for TCP, in which
case GDB sends the 'telnet' BREAK sequence.

   'Ctrl-C', on the other hand, is defined and implemented for all
transport mechanisms.  It is represented by sending the single byte
'0x03' without any of the usual packet overhead described in the
Overview section (*note Overview::).  When a '0x03' byte is transmitted
as part of a packet, it is considered to be packet data and does _not_
represent an interrupt.  E.g., an 'X' packet (*note X packet::), used
for binary downloads, may include an unescaped '0x03' as part of its
packet.

   'BREAK' followed by 'g' is also known as Magic SysRq g.  When Linux
kernel receives this sequence from serial port, it stops execution and
connects to gdb.

   Stubs are not required to recognize these interrupt mechanisms and
the precise meaning associated with receipt of the interrupt is
implementation defined.  If the target supports debugging of multiple
threads and/or processes, it should attempt to interrupt all
currently-executing threads and processes.  If the stub is successful at
interrupting the running program, it should send one of the stop reply
packets (*note Stop Reply Packets::) to GDB as a result of successfully
stopping the program in all-stop mode, and a stop reply for each stopped
thread in non-stop mode.  Interrupts received while the program is
stopped are discarded.


File: gdb.info,  Node: Notification Packets,  Next: Remote Non-Stop,  Prev: Interrupts,  Up: Remote Protocol

E.9 Notification Packets
========================

The GDB remote serial protocol includes "notifications", packets that
require no acknowledgment.  Both the GDB and the stub may send
notifications (although the only notifications defined at present are
sent by the stub).  Notifications carry information without incurring
the round-trip latency of an acknowledgment, and so are useful for
low-impact communications where occasional packet loss is not a problem.

   A notification packet has the form '% DATA # CHECKSUM', where DATA is
the content of the notification, and CHECKSUM is a checksum of DATA,
computed and formatted as for ordinary GDB packets.  A notification's
DATA never contains '$', '%' or '#' characters.  Upon receiving a
notification, the recipient sends no '+' or '-' to acknowledge the
notification's receipt or to report its corruption.

   Every notification's DATA begins with a name, which contains no colon
characters, followed by a colon character.

   Recipients should silently ignore corrupted notifications and
notifications they do not understand.  Recipients should restart timeout
periods on receipt of a well-formed notification, whether or not they
understand it.

   Senders should only send the notifications described here when this
protocol description specifies that they are permitted.  In the future,
we may extend the protocol to permit existing notifications in new
contexts; this rule helps older senders avoid confusing newer
recipients.

   (Older versions of GDB ignore bytes received until they see the '$'
byte that begins an ordinary packet, so new stubs may transmit
notifications without fear of confusing older clients.  There are no
notifications defined for GDB to send at the moment, but we assume that
most older stubs would ignore them, as well.)

   Each notification is comprised of three parts:
'NAME:EVENT'
     The notification packet is sent by the side that initiates the
     exchange (currently, only the stub does that), with EVENT carrying
     the specific information about the notification, and NAME
     specifying the name of the notification.
'ACK'
     The acknowledge sent by the other side, usually GDB, to acknowledge
     the exchange and request the event.

   The purpose of an asynchronous notification mechanism is to report to
GDB that something interesting happened in the remote stub.

   The remote stub may send notification NAME:EVENT at any time, but GDB
acknowledges the notification when appropriate.  The notification event
is pending before GDB acknowledges.  Only one notification at a time may
be pending; if additional events occur before GDB has acknowledged the
previous notification, they must be queued by the stub for later
synchronous transmission in response to ACK packets from GDB.  Because
the notification mechanism is unreliable, the stub is permitted to
resend a notification if it believes GDB may not have received it.

   Specifically, notifications may appear when GDB is not otherwise
reading input from the stub, or when GDB is expecting to read a normal
synchronous response or a '+'/'-' acknowledgment to a packet it has
sent.  Notification packets are distinct from any other communication
from the stub so there is no ambiguity.

   After receiving a notification, GDB shall acknowledge it by sending a
ACK packet as a regular, synchronous request to the stub.  Such
acknowledgment is not required to happen immediately, as GDB is
permitted to send other, unrelated packets to the stub first, which the
stub should process normally.

   Upon receiving a ACK packet, if the stub has other queued events to
report to GDB, it shall respond by sending a normal EVENT.  GDB shall
then send another ACK packet to solicit further responses; again, it is
permitted to send other, unrelated packets as well which the stub should
process normally.

   If the stub receives a ACK packet and there are no additional EVENT
to report, the stub shall return an 'OK' response.  At this point, GDB
has finished processing a notification and the stub has completed
sending any queued events.  GDB won't accept any new notifications until
the final 'OK' is received .  If further notification events occur, the
stub shall send a new notification, GDB shall accept the notification,
and the process shall be repeated.

   The process of asynchronous notification can be illustrated by the
following example:
     <- %%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;
     ...
     -> vStopped
     <- T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;
     -> vStopped
     <- T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;
     -> vStopped
     <- OK

   The following notifications are defined:

NotificationAck     Event                       Description
                                                
Stop      vStopped  REPLY.  The REPLY has the   Report an asynchronous
                    form of a stop reply, as    stop event in non-stop
                    described in *note Stop     mode.
                    Reply Packets::.  Refer     
                    to *note Remote
                    Non-Stop::, for
                    information on how these
                    notifications are
                    acknowledged by GDB.


File: gdb.info,  Node: Remote Non-Stop,  Next: Packet Acknowledgment,  Prev: Notification Packets,  Up: Remote Protocol

E.10 Remote Protocol Support for Non-Stop Mode
==============================================

GDB's remote protocol supports non-stop debugging of multi-threaded
programs, as described in *note Non-Stop Mode::.  If the stub supports
non-stop mode, it should report that to GDB by including 'QNonStop+' in
its 'qSupported' response (*note qSupported::).

   GDB typically sends a 'QNonStop' packet only when establishing a new
connection with the stub.  Entering non-stop mode does not alter the
state of any currently-running threads, but targets must stop all
threads in any already-attached processes when entering all-stop mode.
GDB uses the '?' packet as necessary to probe the target state after a
mode change.

   In non-stop mode, when an attached process encounters an event that
would otherwise be reported with a stop reply, it uses the asynchronous
notification mechanism (*note Notification Packets::) to inform GDB.  In
contrast to all-stop mode, where all threads in all processes are
stopped when a stop reply is sent, in non-stop mode only the thread
reporting the stop event is stopped.  That is, when reporting a 'S' or
'T' response to indicate completion of a step operation, hitting a
breakpoint, or a fault, only the affected thread is stopped; any other
still-running threads continue to run.  When reporting a 'W' or 'X'
response, all running threads belonging to other attached processes
continue to run.

   In non-stop mode, the target shall respond to the '?' packet as
follows.  First, any incomplete stop reply notification/'vStopped'
sequence in progress is abandoned.  The target must begin a new sequence
reporting stop events for all stopped threads, whether or not it has
previously reported those events to GDB.  The first stop reply is sent
as a synchronous reply to the '?' packet, and subsequent stop replies
are sent as responses to 'vStopped' packets using the mechanism
described above.  The target must not send asynchronous stop reply
notifications until the sequence is complete.  If all threads are
running when the target receives the '?' packet, or if the target is not
attached to any process, it shall respond 'OK'.


File: gdb.info,  Node: Packet Acknowledgment,  Next: Examples,  Prev: Remote Non-Stop,  Up: Remote Protocol

E.11 Packet Acknowledgment
==========================

By default, when either the host or the target machine receives a
packet, the first response expected is an acknowledgment: either '+' (to
indicate the package was received correctly) or '-' (to request
retransmission).  This mechanism allows the GDB remote protocol to
operate over unreliable transport mechanisms, such as a serial line.

   In cases where the transport mechanism is itself reliable (such as a
pipe or TCP connection), the '+'/'-' acknowledgments are redundant.  It
may be desirable to disable them in that case to reduce communication
overhead, or for other reasons.  This can be accomplished by means of
the 'QStartNoAckMode' packet; *note QStartNoAckMode::.

   When in no-acknowledgment mode, neither the stub nor GDB shall send
or expect '+'/'-' protocol acknowledgments.  The packet and response
format still includes the normal checksum, as described in *note
Overview::, but the checksum may be ignored by the receiver.

   If the stub supports 'QStartNoAckMode' and prefers to operate in
no-acknowledgment mode, it should report that to GDB by including
'QStartNoAckMode+' in its response to 'qSupported'; *note qSupported::.
If GDB also supports 'QStartNoAckMode' and it has not been disabled via
the 'set remote noack-packet off' command (*note Remote
Configuration::), GDB may then send a 'QStartNoAckMode' packet to the
stub.  Only then may the stub actually turn off packet acknowledgments.
GDB sends a final '+' acknowledgment of the stub's 'OK' response, which
can be safely ignored by the stub.

   Note that 'set remote noack-packet' command only affects negotiation
between GDB and the stub when subsequent connections are made; it does
not affect the protocol acknowledgment state for any current connection.
Since '+'/'-' acknowledgments are enabled by default when a new
connection is established, there is also no protocol request to
re-enable the acknowledgments for the current connection, once disabled.


File: gdb.info,  Node: Examples,  Next: File-I/O Remote Protocol Extension,  Prev: Packet Acknowledgment,  Up: Remote Protocol

E.12 Examples
=============

Example sequence of a target being re-started.  Notice how the restart
does not get any direct output:

     -> R00
     <- +
     _target restarts_
     -> ?
     <- +
     <- T001:1234123412341234
     -> +

   Example sequence of a target being stepped by a single instruction:

     -> G1445...
     <- +
     -> s
     <- +
     _time passes_
     <- T001:1234123412341234
     -> +
     -> g
     <- +
     <- 1455...
     -> +


File: gdb.info,  Node: File-I/O Remote Protocol Extension,  Next: Library List Format,  Prev: Examples,  Up: Remote Protocol

E.13 File-I/O Remote Protocol Extension
=======================================

* Menu:

* File-I/O Overview::
* Protocol Basics::
* The F Request Packet::
* The F Reply Packet::
* The Ctrl-C Message::
* Console I/O::
* List of Supported Calls::
* Protocol-specific Representation of Datatypes::
* Constants::
* File-I/O Examples::


File: gdb.info,  Node: File-I/O Overview,  Next: Protocol Basics,  Up: File-I/O Remote Protocol Extension

E.13.1 File-I/O Overview
------------------------

The "File I/O remote protocol extension" (short: File-I/O) allows the
target to use the host's file system and console I/O to perform various
system calls.  System calls on the target system are translated into a
remote protocol packet to the host system, which then performs the
needed actions and returns a response packet to the target system.  This
simulates file system operations even on targets that lack file systems.

   The protocol is defined to be independent of both the host and target
systems.  It uses its own internal representation of datatypes and
values.  Both GDB and the target's GDB stub are responsible for
translating the system-dependent value representations into the internal
protocol representations when data is transmitted.

   The communication is synchronous.  A system call is possible only
when GDB is waiting for a response from the 'C', 'c', 'S' or 's'
packets.  While GDB handles the request for a system call, the target is
stopped to allow deterministic access to the target's memory.  Therefore
File-I/O is not interruptible by target signals.  On the other hand, it
is possible to interrupt File-I/O by a user interrupt ('Ctrl-C') within
GDB.

   The target's request to perform a host system call does not finish
the latest 'C', 'c', 'S' or 's' action.  That means, after finishing the
system call, the target returns to continuing the previous activity
(continue, step).  No additional continue or step request from GDB is
required.

     (gdb) continue
       <- target requests 'system call X'
       target is stopped, GDB executes system call
       -> GDB returns result
       ... target continues, GDB returns to wait for the target
       <- target hits breakpoint and sends a Txx packet

   The protocol only supports I/O on the console and to regular files on
the host file system.  Character or block special devices, pipes, named
pipes, sockets or any other communication method on the host system are
not supported by this protocol.

   File I/O is not supported in non-stop mode.


File: gdb.info,  Node: Protocol Basics,  Next: The F Request Packet,  Prev: File-I/O Overview,  Up: File-I/O Remote Protocol Extension

E.13.2 Protocol Basics
----------------------

The File-I/O protocol uses the 'F' packet as the request as well as
reply packet.  Since a File-I/O system call can only occur when GDB is
waiting for a response from the continuing or stepping target, the
File-I/O request is a reply that GDB has to expect as a result of a
previous 'C', 'c', 'S' or 's' packet.  This 'F' packet contains all
information needed to allow GDB to call the appropriate host system
call:

   * A unique identifier for the requested system call.

   * All parameters to the system call.  Pointers are given as addresses
     in the target memory address space.  Pointers to strings are given
     as pointer/length pair.  Numerical values are given as they are.
     Numerical control flags are given in a protocol-specific
     representation.

   At this point, GDB has to perform the following actions.

   * If the parameters include pointer values to data needed as input to
     a system call, GDB requests this data from the target with a
     standard 'm' packet request.  This additional communication has to
     be expected by the target implementation and is handled as any
     other 'm' packet.

   * GDB translates all value from protocol representation to host
     representation as needed.  Datatypes are coerced into the host
     types.

   * GDB calls the system call.

   * It then coerces datatypes back to protocol representation.

   * If the system call is expected to return data in buffer space
     specified by pointer parameters to the call, the data is
     transmitted to the target using a 'M' or 'X' packet.  This packet
     has to be expected by the target implementation and is handled as
     any other 'M' or 'X' packet.

   Eventually GDB replies with another 'F' packet which contains all
necessary information for the target to continue.  This at least
contains

   * Return value.

   * 'errno', if has been changed by the system call.

   * "Ctrl-C" flag.

   After having done the needed type and value coercion, the target
continues the latest continue or step action.


File: gdb.info,  Node: The F Request Packet,  Next: The F Reply Packet,  Prev: Protocol Basics,  Up: File-I/O Remote Protocol Extension

E.13.3 The 'F' Request Packet
-----------------------------

The 'F' request packet has the following format:

'FCALL-ID,PARAMETER...'

     CALL-ID is the identifier to indicate the host system call to be
     called.  This is just the name of the function.

     PARAMETER... are the parameters to the system call.  Parameters are
     hexadecimal integer values, either the actual values in case of
     scalar datatypes, pointers to target buffer space in case of
     compound datatypes and unspecified memory areas, or pointer/length
     pairs in case of string parameters.  These are appended to the
     CALL-ID as a comma-delimited list.  All values are transmitted in
     ASCII string representation, pointer/length pairs separated by a
     slash.


File: gdb.info,  Node: The F Reply Packet,  Next: The Ctrl-C Message,  Prev: The F Request Packet,  Up: File-I/O Remote Protocol Extension

E.13.4 The 'F' Reply Packet
---------------------------

The 'F' reply packet has the following format:

'FRETCODE,ERRNO,CTRL-C FLAG;CALL-SPECIFIC ATTACHMENT'

     RETCODE is the return code of the system call as hexadecimal value.

     ERRNO is the 'errno' set by the call, in protocol-specific
     representation.  This parameter can be omitted if the call was
     successful.

     CTRL-C FLAG is only sent if the user requested a break.  In this
     case, ERRNO must be sent as well, even if the call was successful.
     The CTRL-C FLAG itself consists of the character 'C':

          F0,0,C

     or, if the call was interrupted before the host call has been
     performed:

          F-1,4,C

     assuming 4 is the protocol-specific representation of 'EINTR'.


File: gdb.info,  Node: The Ctrl-C Message,  Next: Console I/O,  Prev: The F Reply Packet,  Up: File-I/O Remote Protocol Extension

E.13.5 The 'Ctrl-C' Message
---------------------------

If the 'Ctrl-C' flag is set in the GDB reply packet (*note The F Reply
Packet::), the target should behave as if it had gotten a break message.
The meaning for the target is "system call interrupted by 'SIGINT'".
Consequentially, the target should actually stop (as with a break
message) and return to GDB with a 'T02' packet.

   It's important for the target to know in which state the system call
was interrupted.  There are two possible cases:

   * The system call hasn't been performed on the host yet.

   * The system call on the host has been finished.

   These two states can be distinguished by the target by the value of
the returned 'errno'.  If it's the protocol representation of 'EINTR',
the system call hasn't been performed.  This is equivalent to the
'EINTR' handling on POSIX systems.  In any other case, the target may
presume that the system call has been finished -- successfully or not --
and should behave as if the break message arrived right after the system
call.

   GDB must behave reliably.  If the system call has not been called
yet, GDB may send the 'F' reply immediately, setting 'EINTR' as 'errno'
in the packet.  If the system call on the host has been finished before
the user requests a break, the full action must be finished by GDB.
This requires sending 'M' or 'X' packets as necessary.  The 'F' packet
may only be sent when either nothing has happened or the full action has
been completed.


File: gdb.info,  Node: Console I/O,  Next: List of Supported Calls,  Prev: The Ctrl-C Message,  Up: File-I/O Remote Protocol Extension

E.13.6 Console I/O
------------------

By default and if not explicitly closed by the target system, the file
descriptors 0, 1 and 2 are connected to the GDB console.  Output on the
GDB console is handled as any other file output operation ('write(1,
...)' or 'write(2, ...)').  Console input is handled by GDB so that
after the target read request from file descriptor 0 all following
typing is buffered until either one of the following conditions is met:

   * The user types 'Ctrl-c'.  The behaviour is as explained above, and
     the 'read' system call is treated as finished.

   * The user presses <RET>.  This is treated as end of input with a
     trailing newline.

   * The user types 'Ctrl-d'.  This is treated as end of input.  No
     trailing character (neither newline nor 'Ctrl-D') is appended to
     the input.

   If the user has typed more characters than fit in the buffer given to
the 'read' call, the trailing characters are buffered in GDB until
either another 'read(0, ...)' is requested by the target, or debugging
is stopped at the user's request.


File: gdb.info,  Node: List of Supported Calls,  Next: Protocol-specific Representation of Datatypes,  Prev: Console I/O,  Up: File-I/O Remote Protocol Extension

E.13.7 List of Supported Calls
------------------------------

* Menu:

* open::
* close::
* read::
* write::
* lseek::
* rename::
* unlink::
* stat/fstat::
* gettimeofday::
* isatty::
* system::


File: gdb.info,  Node: open,  Next: close,  Up: List of Supported Calls

open
....

Synopsis:
          int open(const char *pathname, int flags);
          int open(const char *pathname, int flags, mode_t mode);

Request:
     'Fopen,PATHPTR/LEN,FLAGS,MODE'

     FLAGS is the bitwise 'OR' of the following values:

     'O_CREAT'
          If the file does not exist it will be created.  The host rules
          apply as far as file ownership and time stamps are concerned.

     'O_EXCL'
          When used with 'O_CREAT', if the file already exists it is an
          error and open() fails.

     'O_TRUNC'
          If the file already exists and the open mode allows writing
          ('O_RDWR' or 'O_WRONLY' is given) it will be truncated to zero
          length.

     'O_APPEND'
          The file is opened in append mode.

     'O_RDONLY'
          The file is opened for reading only.

     'O_WRONLY'
          The file is opened for writing only.

     'O_RDWR'
          The file is opened for reading and writing.

     Other bits are silently ignored.

     MODE is the bitwise 'OR' of the following values:

     'S_IRUSR'
          User has read permission.

     'S_IWUSR'
          User has write permission.

     'S_IRGRP'
          Group has read permission.

     'S_IWGRP'
          Group has write permission.

     'S_IROTH'
          Others have read permission.

     'S_IWOTH'
          Others have write permission.

     Other bits are silently ignored.

Return value:
     'open' returns the new file descriptor or -1 if an error occurred.

Errors:

     'EEXIST'
          PATHNAME already exists and 'O_CREAT' and 'O_EXCL' were used.

     'EISDIR'
          PATHNAME refers to a directory.

     'EACCES'
          The requested access is not allowed.

     'ENAMETOOLONG'
          PATHNAME was too long.

     'ENOENT'
          A directory component in PATHNAME does not exist.

     'ENODEV'
          PATHNAME refers to a device, pipe, named pipe or socket.

     'EROFS'
          PATHNAME refers to a file on a read-only filesystem and write
          access was requested.

     'EFAULT'
          PATHNAME is an invalid pointer value.

     'ENOSPC'
          No space on device to create the file.

     'EMFILE'
          The process already has the maximum number of files open.

     'ENFILE'
          The limit on the total number of files open on the system has
          been reached.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: close,  Next: read,  Prev: open,  Up: List of Supported Calls

close
.....

Synopsis:
          int close(int fd);

Request:
     'Fclose,FD'

Return value:
     'close' returns zero on success, or -1 if an error occurred.

Errors:

     'EBADF'
          FD isn't a valid open file descriptor.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: read,  Next: write,  Prev: close,  Up: List of Supported Calls

read
....

Synopsis:
          int read(int fd, void *buf, unsigned int count);

Request:
     'Fread,FD,BUFPTR,COUNT'

Return value:
     On success, the number of bytes read is returned.  Zero indicates
     end of file.  If count is zero, read returns zero as well.  On
     error, -1 is returned.

Errors:

     'EBADF'
          FD is not a valid file descriptor or is not open for reading.

     'EFAULT'
          BUFPTR is an invalid pointer value.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: write,  Next: lseek,  Prev: read,  Up: List of Supported Calls

write
.....

Synopsis:
          int write(int fd, const void *buf, unsigned int count);

Request:
     'Fwrite,FD,BUFPTR,COUNT'

Return value:
     On success, the number of bytes written are returned.  Zero
     indicates nothing was written.  On error, -1 is returned.

Errors:

     'EBADF'
          FD is not a valid file descriptor or is not open for writing.

     'EFAULT'
          BUFPTR is an invalid pointer value.

     'EFBIG'
          An attempt was made to write a file that exceeds the
          host-specific maximum file size allowed.

     'ENOSPC'
          No space on device to write the data.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: lseek,  Next: rename,  Prev: write,  Up: List of Supported Calls

lseek
.....

Synopsis:
          long lseek (int fd, long offset, int flag);

Request:
     'Flseek,FD,OFFSET,FLAG'

     FLAG is one of:

     'SEEK_SET'
          The offset is set to OFFSET bytes.

     'SEEK_CUR'
          The offset is set to its current location plus OFFSET bytes.

     'SEEK_END'
          The offset is set to the size of the file plus OFFSET bytes.

Return value:
     On success, the resulting unsigned offset in bytes from the
     beginning of the file is returned.  Otherwise, a value of -1 is
     returned.

Errors:

     'EBADF'
          FD is not a valid open file descriptor.

     'ESPIPE'
          FD is associated with the GDB console.

     'EINVAL'
          FLAG is not a proper value.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: rename,  Next: unlink,  Prev: lseek,  Up: List of Supported Calls

rename
......

Synopsis:
          int rename(const char *oldpath, const char *newpath);

Request:
     'Frename,OLDPATHPTR/LEN,NEWPATHPTR/LEN'

Return value:
     On success, zero is returned.  On error, -1 is returned.

Errors:

     'EISDIR'
          NEWPATH is an existing directory, but OLDPATH is not a
          directory.

     'EEXIST'
          NEWPATH is a non-empty directory.

     'EBUSY'
          OLDPATH or NEWPATH is a directory that is in use by some
          process.

     'EINVAL'
          An attempt was made to make a directory a subdirectory of
          itself.

     'ENOTDIR'
          A component used as a directory in OLDPATH or new path is not
          a directory.  Or OLDPATH is a directory and NEWPATH exists but
          is not a directory.

     'EFAULT'
          OLDPATHPTR or NEWPATHPTR are invalid pointer values.

     'EACCES'
          No access to the file or the path of the file.

     'ENAMETOOLONG'

          OLDPATH or NEWPATH was too long.

     'ENOENT'
          A directory component in OLDPATH or NEWPATH does not exist.

     'EROFS'
          The file is on a read-only filesystem.

     'ENOSPC'
          The device containing the file has no room for the new
          directory entry.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: unlink,  Next: stat/fstat,  Prev: rename,  Up: List of Supported Calls

unlink
......

Synopsis:
          int unlink(const char *pathname);

Request:
     'Funlink,PATHNAMEPTR/LEN'

Return value:
     On success, zero is returned.  On error, -1 is returned.

Errors:

     'EACCES'
          No access to the file or the path of the file.

     'EPERM'
          The system does not allow unlinking of directories.

     'EBUSY'
          The file PATHNAME cannot be unlinked because it's being used
          by another process.

     'EFAULT'
          PATHNAMEPTR is an invalid pointer value.

     'ENAMETOOLONG'
          PATHNAME was too long.

     'ENOENT'
          A directory component in PATHNAME does not exist.

     'ENOTDIR'
          A component of the path is not a directory.

     'EROFS'
          The file is on a read-only filesystem.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: stat/fstat,  Next: gettimeofday,  Prev: unlink,  Up: List of Supported Calls

stat/fstat
..........

Synopsis:
          int stat(const char *pathname, struct stat *buf);
          int fstat(int fd, struct stat *buf);

Request:
     'Fstat,PATHNAMEPTR/LEN,BUFPTR'
     'Ffstat,FD,BUFPTR'

Return value:
     On success, zero is returned.  On error, -1 is returned.

Errors:

     'EBADF'
          FD is not a valid open file.

     'ENOENT'
          A directory component in PATHNAME does not exist or the path
          is an empty string.

     'ENOTDIR'
          A component of the path is not a directory.

     'EFAULT'
          PATHNAMEPTR is an invalid pointer value.

     'EACCES'
          No access to the file or the path of the file.

     'ENAMETOOLONG'
          PATHNAME was too long.

     'EINTR'
          The call was interrupted by the user.


File: gdb.info,  Node: gettimeofday,  Next: isatty,  Prev: stat/fstat,  Up: List of Supported Calls

gettimeofday
............

Synopsis:
          int gettimeofday(struct timeval *tv, void *tz);

Request:
     'Fgettimeofday,TVPTR,TZPTR'

Return value:
     On success, 0 is returned, -1 otherwise.

Errors:

     'EINVAL'
          TZ is a non-NULL pointer.

     'EFAULT'
          TVPTR and/or TZPTR is an invalid pointer value.


File: gdb.info,  Node: isatty,  Next: system,  Prev: gettimeofday,  Up: List of Supported Calls

isatty
......

Synopsis:
          int isatty(int fd);

Request:
     'Fisatty,FD'

Return value:
     Returns 1 if FD refers to the GDB console, 0 otherwise.

Errors:

     'EINTR'
          The call was interrupted by the user.

   Note that the 'isatty' call is treated as a special case: it returns
1 to the target if the file descriptor is attached to the GDB console, 0
otherwise.  Implementing through system calls would require implementing
'ioctl' and would be more complex than needed.


File: gdb.info,  Node: system,  Prev: isatty,  Up: List of Supported Calls

system
......

Synopsis:
          int system(const char *command);

Request:
     'Fsystem,COMMANDPTR/LEN'

Return value:
     If LEN is zero, the return value indicates whether a shell is
     available.  A zero return value indicates a shell is not available.
     For non-zero LEN, the value returned is -1 on error and the return
     status of the command otherwise.  Only the exit status of the
     command is returned, which is extracted from the host's 'system'
     return value by calling 'WEXITSTATUS(retval)'.  In case '/bin/sh'
     could not be executed, 127 is returned.

Errors:

     'EINTR'
          The call was interrupted by the user.

   GDB takes over the full task of calling the necessary host calls to
perform the 'system' call.  The return value of 'system' on the host is
simplified before it's returned to the target.  Any termination signal
information from the child process is discarded, and the return value
consists entirely of the exit status of the called command.

   Due to security concerns, the 'system' call is by default refused by
GDB.  The user has to allow this call explicitly with the 'set remote
system-call-allowed 1' command.

'set remote system-call-allowed'
     Control whether to allow the 'system' calls in the File I/O
     protocol for the remote target.  The default is zero (disabled).

'show remote system-call-allowed'
     Show whether the 'system' calls are allowed in the File I/O
     protocol.


File: gdb.info,  Node: Protocol-specific Representation of Datatypes,  Next: Constants,  Prev: List of Supported Calls,  Up: File-I/O Remote Protocol Extension

E.13.8 Protocol-specific Representation of Datatypes
----------------------------------------------------

* Menu:

* Integral Datatypes::
* Pointer Values::
* Memory Transfer::
* struct stat::
* struct timeval::


File: gdb.info,  Node: Integral Datatypes,  Next: Pointer Values,  Up: Protocol-specific Representation of Datatypes

Integral Datatypes
..................

The integral datatypes used in the system calls are 'int', 'unsigned
int', 'long', 'unsigned long', 'mode_t', and 'time_t'.

   'int', 'unsigned int', 'mode_t' and 'time_t' are implemented as 32
bit values in this protocol.

   'long' and 'unsigned long' are implemented as 64 bit types.

   *Note Limits::, for corresponding MIN and MAX values (similar to
those in 'limits.h') to allow range checking on host and target.

   'time_t' datatypes are defined as seconds since the Epoch.

   All integral datatypes transferred as part of a memory read or write
of a structured datatype e.g. a 'struct stat' have to be given in big
endian byte order.


File: gdb.info,  Node: Pointer Values,  Next: Memory Transfer,  Prev: Integral Datatypes,  Up: Protocol-specific Representation of Datatypes

Pointer Values
..............

Pointers to target data are transmitted as they are.  An exception is
made for pointers to buffers for which the length isn't transmitted as
part of the function call, namely strings.  Strings are transmitted as a
pointer/length pair, both as hex values, e.g.

     1aaf/12

which is a pointer to data of length 18 bytes at position 0x1aaf.  The
length is defined as the full string length in bytes, including the
trailing null byte.  For example, the string '"hello world"' at address
0x123456 is transmitted as

     123456/d


File: gdb.info,  Node: Memory Transfer,  Next: struct stat,  Prev: Pointer Values,  Up: Protocol-specific Representation of Datatypes

Memory Transfer
...............

Structured data which is transferred using a memory read or write (for
example, a 'struct stat') is expected to be in a protocol-specific
format with all scalar multibyte datatypes being big endian.
Translation to this representation needs to be done both by the target
before the 'F' packet is sent, and by GDB before it transfers memory to
the target.  Transferred pointers to structured data should point to the
already-coerced data at any time.


File: gdb.info,  Node: struct stat,  Next: struct timeval,  Prev: Memory Transfer,  Up: Protocol-specific Representation of Datatypes

struct stat
...........

The buffer of type 'struct stat' used by the target and GDB is defined
as follows:

     struct stat {
         unsigned int  st_dev;      /* device */
         unsigned int  st_ino;      /* inode */
         mode_t        st_mode;     /* protection */
         unsigned int  st_nlink;    /* number of hard links */
         unsigned int  st_uid;      /* user ID of owner */
         unsigned int  st_gid;      /* group ID of owner */
         unsigned int  st_rdev;     /* device type (if inode device) */
         unsigned long st_size;     /* total size, in bytes */
         unsigned long st_blksize;  /* blocksize for filesystem I/O */
         unsigned long st_blocks;   /* number of blocks allocated */
         time_t        st_atime;    /* time of last access */
         time_t        st_mtime;    /* time of last modification */
         time_t        st_ctime;    /* time of last change */
     };

   The integral datatypes conform to the definitions given in the
appropriate section (see *note Integral Datatypes::, for details) so
this structure is of size 64 bytes.

   The values of several fields have a restricted meaning and/or range
of values.

'st_dev'
     A value of 0 represents a file, 1 the console.

'st_ino'
     No valid meaning for the target.  Transmitted unchanged.

'st_mode'
     Valid mode bits are described in *note Constants::.  Any other bits
     have currently no meaning for the target.

'st_uid'
'st_gid'
'st_rdev'
     No valid meaning for the target.  Transmitted unchanged.

'st_atime'
'st_mtime'
'st_ctime'
     These values have a host and file system dependent accuracy.
     Especially on Windows hosts, the file system may not support exact
     timing values.

   The target gets a 'struct stat' of the above representation and is
responsible for coercing it to the target representation before
continuing.

   Note that due to size differences between the host, target, and
protocol representations of 'struct stat' members, these members could
eventually get truncated on the target.


File: gdb.info,  Node: struct timeval,  Prev: struct stat,  Up: Protocol-specific Representation of Datatypes

struct timeval
..............

The buffer of type 'struct timeval' used by the File-I/O protocol is
defined as follows:

     struct timeval {
         time_t tv_sec;  /* second */
         long   tv_usec; /* microsecond */
     };

   The integral datatypes conform to the definitions given in the
appropriate section (see *note Integral Datatypes::, for details) so
this structure is of size 8 bytes.


File: gdb.info,  Node: Constants,  Next: File-I/O Examples,  Prev: Protocol-specific Representation of Datatypes,  Up: File-I/O Remote Protocol Extension

E.13.9 Constants
----------------

The following values are used for the constants inside of the protocol.
GDB and target are responsible for translating these values before and
after the call as needed.

* Menu:

* Open Flags::
* mode_t Values::
* Errno Values::
* Lseek Flags::
* Limits::


File: gdb.info,  Node: Open Flags,  Next: mode_t Values,  Up: Constants

Open Flags
..........

All values are given in hexadecimal representation.

       O_RDONLY        0x0
       O_WRONLY        0x1
       O_RDWR          0x2
       O_APPEND        0x8
       O_CREAT       0x200
       O_TRUNC       0x400
       O_EXCL        0x800


File: gdb.info,  Node: mode_t Values,  Next: Errno Values,  Prev: Open Flags,  Up: Constants

mode_t Values
.............

All values are given in octal representation.

       S_IFREG       0100000
       S_IFDIR        040000
       S_IRUSR          0400
       S_IWUSR          0200
       S_IXUSR          0100
       S_IRGRP           040
       S_IWGRP           020
       S_IXGRP           010
       S_IROTH            04
       S_IWOTH            02
       S_IXOTH            01


File: gdb.info,  Node: Errno Values,  Next: Lseek Flags,  Prev: mode_t Values,  Up: Constants

Errno Values
............

All values are given in decimal representation.

       EPERM           1
       ENOENT          2
       EINTR           4
       EBADF           9
       EACCES         13
       EFAULT         14
       EBUSY          16
       EEXIST         17
       ENODEV         19
       ENOTDIR        20
       EISDIR         21
       EINVAL         22
       ENFILE         23
       EMFILE         24
       EFBIG          27
       ENOSPC         28
       ESPIPE         29
       EROFS          30
       ENAMETOOLONG   91
       EUNKNOWN       9999

   'EUNKNOWN' is used as a fallback error value if a host system returns
any error value not in the list of supported error numbers.


File: gdb.info,  Node: Lseek Flags,  Next: Limits,  Prev: Errno Values,  Up: Constants

Lseek Flags
...........

       SEEK_SET      0
       SEEK_CUR      1
       SEEK_END      2


File: gdb.info,  Node: Limits,  Prev: Lseek Flags,  Up: Constants

Limits
......

All values are given in decimal representation.

       INT_MIN       -2147483648
       INT_MAX        2147483647
       UINT_MAX       4294967295
       LONG_MIN      -9223372036854775808
       LONG_MAX       9223372036854775807
       ULONG_MAX      18446744073709551615


File: gdb.info,  Node: File-I/O Examples,  Prev: Constants,  Up: File-I/O Remote Protocol Extension

E.13.10 File-I/O Examples
-------------------------

Example sequence of a write call, file descriptor 3, buffer is at target
address 0x1234, 6 bytes should be written:

     <- Fwrite,3,1234,6
     _request memory read from target_
     -> m1234,6
     <- XXXXXX
     _return "6 bytes written"_
     -> F6

   Example sequence of a read call, file descriptor 3, buffer is at
target address 0x1234, 6 bytes should be read:

     <- Fread,3,1234,6
     _request memory write to target_
     -> X1234,6:XXXXXX
     _return "6 bytes read"_
     -> F6

   Example sequence of a read call, call fails on the host due to
invalid file descriptor ('EBADF'):

     <- Fread,3,1234,6
     -> F-1,9

   Example sequence of a read call, user presses 'Ctrl-c' before syscall
on host is called:

     <- Fread,3,1234,6
     -> F-1,4,C
     <- T02

   Example sequence of a read call, user presses 'Ctrl-c' after syscall
on host is called:

     <- Fread,3,1234,6
     -> X1234,6:XXXXXX
     <- T02


File: gdb.info,  Node: Library List Format,  Next: Library List Format for SVR4 Targets,  Prev: File-I/O Remote Protocol Extension,  Up: Remote Protocol

E.14 Library List Format
========================

On some platforms, a dynamic loader (e.g. 'ld.so') runs in the same
process as your application to manage libraries.  In this case, GDB can
use the loader's symbol table and normal memory operations to maintain a
list of shared libraries.  On other platforms, the operating system
manages loaded libraries.  GDB can not retrieve the list of currently
loaded libraries through memory operations, so it uses the
'qXfer:libraries:read' packet (*note qXfer library list read::) instead.
The remote stub queries the target's operating system and reports which
libraries are loaded.

   The 'qXfer:libraries:read' packet returns an XML document which lists
loaded libraries and their offsets.  Each library has an associated name
and one or more segment or section base addresses, which report where
the library was loaded in memory.

   For the common case of libraries that are fully linked binaries, the
library should have a list of segments.  If the target supports dynamic
linking of a relocatable object file, its library XML element should
instead include a list of allocated sections.  The segment or section
bases are start addresses, not relocation offsets; they do not depend on
the library's link-time base addresses.

   GDB must be linked with the Expat library to support XML library
lists.  *Note Expat::.

   A simple memory map, with one loaded library relocated by a single
offset, looks like this:

     <library-list>
       <library name="/lib/libc.so.6">
         <segment address="0x10000000"/>
       </library>
     </library-list>

   Another simple memory map, with one loaded library with three
allocated sections (.text, .data, .bss), looks like this:

     <library-list>
       <library name="sharedlib.o">
         <section address="0x10000000"/>
         <section address="0x20000000"/>
         <section address="0x30000000"/>
       </library>
     </library-list>

   The format of a library list is described by this DTD:

     <!-- library-list: Root element with versioning -->
     <!ELEMENT library-list  (library)*>
     <!ATTLIST library-list  version CDATA   #FIXED  "1.0">
     <!ELEMENT library       (segment*, section*)>
     <!ATTLIST library       name    CDATA   #REQUIRED>
     <!ELEMENT segment       EMPTY>
     <!ATTLIST segment       address CDATA   #REQUIRED>
     <!ELEMENT section       EMPTY>
     <!ATTLIST section       address CDATA   #REQUIRED>

   In addition, segments and section descriptors cannot be mixed within
a single library element, and you must supply at least one segment or
section for each library.


File: gdb.info,  Node: Library List Format for SVR4 Targets,  Next: Memory Map Format,  Prev: Library List Format,  Up: Remote Protocol

E.15 Library List Format for SVR4 Targets
=========================================

On SVR4 platforms GDB can use the symbol table of a dynamic loader (e.g.
'ld.so') and normal memory operations to maintain a list of shared
libraries.  Still a special library list provided by this packet is more
efficient for the GDB remote protocol.

   The 'qXfer:libraries-svr4:read' packet returns an XML document which
lists loaded libraries and their SVR4 linker parameters.  For each
library on SVR4 target, the following parameters are reported:

   - 'name', the absolute file name from the 'l_name' field of 'struct
     link_map'.
   - 'lm' with address of 'struct link_map' used for TLS (Thread Local
     Storage) access.
   - 'l_addr', the displacement as read from the field 'l_addr' of
     'struct link_map'.  For prelinked libraries this is not an absolute
     memory address.  It is a displacement of absolute memory address
     against address the file was prelinked to during the library load.
   - 'l_ld', which is memory address of the 'PT_DYNAMIC' segment

   Additionally the single 'main-lm' attribute specifies address of
'struct link_map' used for the main executable.  This parameter is used
for TLS access and its presence is optional.

   GDB must be linked with the Expat library to support XML SVR4 library
lists.  *Note Expat::.

   A simple memory map, with two loaded libraries (which do not use
prelink), looks like this:

     <library-list-svr4 version="1.0" main-lm="0xe4f8f8">
       <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
                l_ld="0xe4eefc"/>
       <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
                l_ld="0x152350"/>
     </library-list-svr>

   The format of an SVR4 library list is described by this DTD:

     <!-- library-list-svr4: Root element with versioning -->
     <!ELEMENT library-list-svr4  (library)*>
     <!ATTLIST library-list-svr4  version CDATA   #FIXED  "1.0">
     <!ATTLIST library-list-svr4  main-lm CDATA   #IMPLIED>
     <!ELEMENT library            EMPTY>
     <!ATTLIST library            name    CDATA   #REQUIRED>
     <!ATTLIST library            lm      CDATA   #REQUIRED>
     <!ATTLIST library            l_addr  CDATA   #REQUIRED>
     <!ATTLIST library            l_ld    CDATA   #REQUIRED>


File: gdb.info,  Node: Memory Map Format,  Next: Thread List Format,  Prev: Library List Format for SVR4 Targets,  Up: Remote Protocol

E.16 Memory Map Format
======================

To be able to write into flash memory, GDB needs to obtain a memory map
from the target.  This section describes the format of the memory map.

   The memory map is obtained using the 'qXfer:memory-map:read' (*note
qXfer memory map read::) packet and is an XML document that lists memory
regions.

   GDB must be linked with the Expat library to support XML memory maps.
*Note Expat::.

   The top-level structure of the document is shown below:

     <?xml version="1.0"?>
     <!DOCTYPE memory-map
               PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
                      "http://sourceware.org/gdb/gdb-memory-map.dtd">
     <memory-map>
         region...
     </memory-map>

   Each region can be either:

   * A region of RAM starting at ADDR and extending for LENGTH bytes
     from there:

          <memory type="ram" start="ADDR" length="LENGTH"/>

   * A region of read-only memory:

          <memory type="rom" start="ADDR" length="LENGTH"/>

   * A region of flash memory, with erasure blocks BLOCKSIZE bytes in
     length:

          <memory type="flash" start="ADDR" length="LENGTH">
            <property name="blocksize">BLOCKSIZE</property>
          </memory>

   Regions must not overlap.  GDB assumes that areas of memory not
covered by the memory map are RAM, and uses the ordinary 'M' and 'X'
packets to write to addresses in such ranges.

   The formal DTD for memory map format is given below:

     <!-- ................................................... -->
     <!-- Memory Map XML DTD ................................ -->
     <!-- File: memory-map.dtd .............................. -->
     <!-- .................................... .............. -->
     <!-- memory-map.dtd -->
     <!-- memory-map: Root element with versioning -->
     <!ELEMENT memory-map (memory | property)>
     <!ATTLIST memory-map    version CDATA   #FIXED  "1.0.0">
     <!ELEMENT memory (property)>
     <!-- memory: Specifies a memory region,
                  and its type, or device. -->
     <!ATTLIST memory        type    CDATA   #REQUIRED
                             start   CDATA   #REQUIRED
                             length  CDATA   #REQUIRED
                             device  CDATA   #IMPLIED>
     <!-- property: Generic attribute tag -->
     <!ELEMENT property (#PCDATA | property)*>
     <!ATTLIST property      name    CDATA   #REQUIRED>


File: gdb.info,  Node: Thread List Format,  Next: Traceframe Info Format,  Prev: Memory Map Format,  Up: Remote Protocol

E.17 Thread List Format
=======================

To efficiently update the list of threads and their attributes, GDB
issues the 'qXfer:threads:read' packet (*note qXfer threads read::) and
obtains the XML document with the following structure:

     <?xml version="1.0"?>
     <threads>
         <thread id="id" core="0">
         ... description ...
         </thread>
     </threads>

   Each 'thread' element must have the 'id' attribute that identifies
the thread (*note thread-id syntax::).  The 'core' attribute, if
present, specifies which processor core the thread was last executing
on.  The content of the of 'thread' element is interpreted as
human-readable auxilliary information.


File: gdb.info,  Node: Traceframe Info Format,  Next: Branch Trace Format,  Prev: Thread List Format,  Up: Remote Protocol

E.18 Traceframe Info Format
===========================

To be able to know which objects in the inferior can be examined when
inspecting a tracepoint hit, GDB needs to obtain the list of memory
ranges, registers and trace state variables that have been collected in
a traceframe.

   This list is obtained using the 'qXfer:traceframe-info:read' (*note
qXfer traceframe info read::) packet and is an XML document.

   GDB must be linked with the Expat library to support XML traceframe
info discovery.  *Note Expat::.

   The top-level structure of the document is shown below:

     <?xml version="1.0"?>
     <!DOCTYPE traceframe-info
               PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
                      "http://sourceware.org/gdb/gdb-traceframe-info.dtd">
     <traceframe-info>
        block...
     </traceframe-info>

   Each traceframe block can be either:

   * A region of collected memory starting at ADDR and extending for
     LENGTH bytes from there:

          <memory start="ADDR" length="LENGTH"/>

   * A block indicating trace state variable numbered NUMBER has been
     collected:

          <tvar id="NUMBER"/>

   The formal DTD for the traceframe info format is given below:

     <!ELEMENT traceframe-info  (memory | tvar)* >
     <!ATTLIST traceframe-info  version CDATA   #FIXED  "1.0">

     <!ELEMENT memory        EMPTY>
     <!ATTLIST memory        start   CDATA   #REQUIRED
                             length  CDATA   #REQUIRED>
     <!ELEMENT tvar>
     <!ATTLIST tvar          id      CDATA   #REQUIRED>


File: gdb.info,  Node: Branch Trace Format,  Prev: Traceframe Info Format,  Up: Remote Protocol

E.19 Branch Trace Format
========================

In order to display the branch trace of an inferior thread, GDB needs to
obtain the list of branches.  This list is represented as list of
sequential code blocks that are connected via branches.  The code in
each block has been executed sequentially.

   This list is obtained using the 'qXfer:btrace:read' (*note qXfer
btrace read::) packet and is an XML document.

   GDB must be linked with the Expat library to support XML traceframe
info discovery.  *Note Expat::.

   The top-level structure of the document is shown below:

     <?xml version="1.0"?>
     <!DOCTYPE btrace
               PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN"
                      "http://sourceware.org/gdb/gdb-btrace.dtd">
     <btrace>
        block...
     </btrace>

   * A block of sequentially executed instructions starting at BEGIN and
     ending at END:

          <block begin="BEGIN" end="END"/>

   The formal DTD for the branch trace format is given below:

     <!ELEMENT btrace  (block)* >
     <!ATTLIST btrace  version CDATA   #FIXED "1.0">

     <!ELEMENT block        EMPTY>
     <!ATTLIST block        begin  CDATA   #REQUIRED
                            end    CDATA   #REQUIRED>


File: gdb.info,  Node: Agent Expressions,  Next: Target Descriptions,  Prev: Remote Protocol,  Up: Top

Appendix F The GDB Agent Expression Mechanism
*********************************************

In some applications, it is not feasible for the debugger to interrupt
the program's execution long enough for the developer to learn anything
helpful about its behavior.  If the program's correctness depends on its
real-time behavior, delays introduced by a debugger might cause the
program to fail, even when the code itself is correct.  It is useful to
be able to observe the program's behavior without interrupting it.

   Using GDB's 'trace' and 'collect' commands, the user can specify
locations in the program, and arbitrary expressions to evaluate when
those locations are reached.  Later, using the 'tfind' command, she can
examine the values those expressions had when the program hit the trace
points.  The expressions may also denote objects in memory -- structures
or arrays, for example -- whose values GDB should record; while visiting
a particular tracepoint, the user may inspect those objects as if they
were in memory at that moment.  However, because GDB records these
values without interacting with the user, it can do so quickly and
unobtrusively, hopefully not disturbing the program's behavior.

   When GDB is debugging a remote target, the GDB "agent" code running
on the target computes the values of the expressions itself.  To avoid
having a full symbolic expression evaluator on the agent, GDB translates
expressions in the source language into a simpler bytecode language, and
then sends the bytecode to the agent; the agent then executes the
bytecode, and records the values for GDB to retrieve later.

   The bytecode language is simple; there are forty-odd opcodes, the
bulk of which are the usual vocabulary of C operands (addition,
subtraction, shifts, and so on) and various sizes of literals and memory
reference operations.  The bytecode interpreter operates strictly on
machine-level values -- various sizes of integers and floating point
numbers -- and requires no information about types or symbols; thus, the
interpreter's internal data structures are simple, and each bytecode
requires only a few native machine instructions to implement it.  The
interpreter is small, and strict limits on the memory and time required
to evaluate an expression are easy to determine, making it suitable for
use by the debugging agent in real-time applications.

* Menu:

* General Bytecode Design::     Overview of the interpreter.
* Bytecode Descriptions::       What each one does.
* Using Agent Expressions::     How agent expressions fit into the big picture.
* Varying Target Capabilities:: How to discover what the target can do.
* Rationale::                   Why we did it this way.


File: gdb.info,  Node: General Bytecode Design,  Next: Bytecode Descriptions,  Up: Agent Expressions

F.1 General Bytecode Design
===========================

The agent represents bytecode expressions as an array of bytes.  Each
instruction is one byte long (thus the term "bytecode").  Some
instructions are followed by operand bytes; for example, the 'goto'
instruction is followed by a destination for the jump.

   The bytecode interpreter is a stack-based machine; most instructions
pop their operands off the stack, perform some operation, and push the
result back on the stack for the next instruction to consume.  Each
element of the stack may contain either a integer or a floating point
value; these values are as many bits wide as the largest integer that
can be directly manipulated in the source language.  Stack elements
carry no record of their type; bytecode could push a value as an
integer, then pop it as a floating point value.  However, GDB will not
generate code which does this.  In C, one might define the type of a
stack element as follows:
     union agent_val {
       LONGEST l;
       DOUBLEST d;
     };
where 'LONGEST' and 'DOUBLEST' are 'typedef' names for the largest
integer and floating point types on the machine.

   By the time the bytecode interpreter reaches the end of the
expression, the value of the expression should be the only value left on
the stack.  For tracing applications, 'trace' bytecodes in the
expression will have recorded the necessary data, and the value on the
stack may be discarded.  For other applications, like conditional
breakpoints, the value may be useful.

   Separate from the stack, the interpreter has two registers:
'pc'
     The address of the next bytecode to execute.

'start'
     The address of the start of the bytecode expression, necessary for
     interpreting the 'goto' and 'if_goto' instructions.

Neither of these registers is directly visible to the bytecode language
itself, but they are useful for defining the meanings of the bytecode
operations.

   There are no instructions to perform side effects on the running
program, or call the program's functions; we assume that these
expressions are only used for unobtrusive debugging, not for patching
the running code.

   Most bytecode instructions do not distinguish between the various
sizes of values, and operate on full-width values; the upper bits of the
values are simply ignored, since they do not usually make a difference
to the value computed.  The exceptions to this rule are:

memory reference instructions ('ref'N)
     There are distinct instructions to fetch different word sizes from
     memory.  Once on the stack, however, the values are treated as
     full-size integers.  They may need to be sign-extended; the 'ext'
     instruction exists for this purpose.

the sign-extension instruction ('ext' N)
     These clearly need to know which portion of their operand is to be
     extended to occupy the full length of the word.

   If the interpreter is unable to evaluate an expression completely for
some reason (a memory location is inaccessible, or a divisor is zero,
for example), we say that interpretation "terminates with an error".
This means that the problem is reported back to the interpreter's caller
in some helpful way.  In general, code using agent expressions should
assume that they may attempt to divide by zero, fetch arbitrary memory
locations, and misbehave in other ways.

   Even complicated C expressions compile to a few bytecode
instructions; for example, the expression 'x + y * z' would typically
produce code like the following, assuming that 'x' and 'y' live in
registers, and 'z' is a global variable holding a 32-bit 'int':
     reg 1
     reg 2
     const32 address of z
     ref32
     ext 32
     mul
     add
     end

   In detail, these mean:

'reg 1'
     Push the value of register 1 (presumably holding 'x') onto the
     stack.

'reg 2'
     Push the value of register 2 (holding 'y').

'const32 address of z'
     Push the address of 'z' onto the stack.

'ref32'
     Fetch a 32-bit word from the address at the top of the stack;
     replace the address on the stack with the value.  Thus, we replace
     the address of 'z' with 'z''s value.

'ext 32'
     Sign-extend the value on the top of the stack from 32 bits to full
     length.  This is necessary because 'z' is a signed integer.

'mul'
     Pop the top two numbers on the stack, multiply them, and push their
     product.  Now the top of the stack contains the value of the
     expression 'y * z'.

'add'
     Pop the top two numbers, add them, and push the sum.  Now the top
     of the stack contains the value of 'x + y * z'.

'end'
     Stop executing; the value left on the stack top is the value to be
     recorded.


File: gdb.info,  Node: Bytecode Descriptions,  Next: Using Agent Expressions,  Prev: General Bytecode Design,  Up: Agent Expressions

F.2 Bytecode Descriptions
=========================

Each bytecode description has the following form:

'add' (0x02): A B => A+B

     Pop the top two stack items, A and B, as integers; push their sum,
     as an integer.

   In this example, 'add' is the name of the bytecode, and '(0x02)' is
the one-byte value used to encode the bytecode, in hexadecimal.  The
phrase "A B => A+B" shows the stack before and after the bytecode
executes.  Beforehand, the stack must contain at least two values, A and
B; since the top of the stack is to the right, B is on the top of the
stack, and A is underneath it.  After execution, the bytecode will have
popped A and B from the stack, and replaced them with a single value,
A+B.  There may be other values on the stack below those shown, but the
bytecode affects only those shown.

   Here is another example:

'const8' (0x22) N: => N
     Push the 8-bit integer constant N on the stack, without sign
     extension.

   In this example, the bytecode 'const8' takes an operand N directly
from the bytecode stream; the operand follows the 'const8' bytecode
itself.  We write any such operands immediately after the name of the
bytecode, before the colon, and describe the exact encoding of the
operand in the bytecode stream in the body of the bytecode description.

   For the 'const8' bytecode, there are no stack items given before the
=>; this simply means that the bytecode consumes no values from the
stack.  If a bytecode consumes no values, or produces no values, the
list on either side of the => may be empty.

   If a value is written as A, B, or N, then the bytecode treats it as
an integer.  If a value is written is ADDR, then the bytecode treats it
as an address.

   We do not fully describe the floating point operations here; although
this design can be extended in a clean way to handle floating point
values, they are not of immediate interest to the customer, so we avoid
describing them, to save time.

'float' (0x01): =>

     Prefix for floating-point bytecodes.  Not implemented yet.

'add' (0x02): A B => A+B
     Pop two integers from the stack, and push their sum, as an integer.

'sub' (0x03): A B => A-B
     Pop two integers from the stack, subtract the top value from the
     next-to-top value, and push the difference.

'mul' (0x04): A B => A*B
     Pop two integers from the stack, multiply them, and push the
     product on the stack.  Note that, when one multiplies two N-bit
     numbers yielding another N-bit number, it is irrelevant whether the
     numbers are signed or not; the results are the same.

'div_signed' (0x05): A B => A/B
     Pop two signed integers from the stack; divide the next-to-top
     value by the top value, and push the quotient.  If the divisor is
     zero, terminate with an error.

'div_unsigned' (0x06): A B => A/B
     Pop two unsigned integers from the stack; divide the next-to-top
     value by the top value, and push the quotient.  If the divisor is
     zero, terminate with an error.

'rem_signed' (0x07): A B => A MODULO B
     Pop two signed integers from the stack; divide the next-to-top
     value by the top value, and push the remainder.  If the divisor is
     zero, terminate with an error.

'rem_unsigned' (0x08): A B => A MODULO B
     Pop two unsigned integers from the stack; divide the next-to-top
     value by the top value, and push the remainder.  If the divisor is
     zero, terminate with an error.

'lsh' (0x09): A B => A<<B
     Pop two integers from the stack; let A be the next-to-top value,
     and B be the top value.  Shift A left by B bits, and push the
     result.

'rsh_signed' (0x0a): A B => '(signed)'A>>B
     Pop two integers from the stack; let A be the next-to-top value,
     and B be the top value.  Shift A right by B bits, inserting copies
     of the top bit at the high end, and push the result.

'rsh_unsigned' (0x0b): A B => A>>B
     Pop two integers from the stack; let A be the next-to-top value,
     and B be the top value.  Shift A right by B bits, inserting zero
     bits at the high end, and push the result.

'log_not' (0x0e): A => !A
     Pop an integer from the stack; if it is zero, push the value one;
     otherwise, push the value zero.

'bit_and' (0x0f): A B => A&B
     Pop two integers from the stack, and push their bitwise 'and'.

'bit_or' (0x10): A B => A|B
     Pop two integers from the stack, and push their bitwise 'or'.

'bit_xor' (0x11): A B => A^B
     Pop two integers from the stack, and push their bitwise
     exclusive-'or'.

'bit_not' (0x12): A => ~A
     Pop an integer from the stack, and push its bitwise complement.

'equal' (0x13): A B => A=B
     Pop two integers from the stack; if they are equal, push the value
     one; otherwise, push the value zero.

'less_signed' (0x14): A B => A<B
     Pop two signed integers from the stack; if the next-to-top value is
     less than the top value, push the value one; otherwise, push the
     value zero.

'less_unsigned' (0x15): A B => A<B
     Pop two unsigned integers from the stack; if the next-to-top value
     is less than the top value, push the value one; otherwise, push the
     value zero.

'ext' (0x16) N: A => A, sign-extended from N bits
     Pop an unsigned value from the stack; treating it as an N-bit
     twos-complement value, extend it to full length.  This means that
     all bits to the left of bit N-1 (where the least significant bit is
     bit 0) are set to the value of bit N-1.  Note that N may be larger
     than or equal to the width of the stack elements of the bytecode
     engine; in this case, the bytecode should have no effect.

     The number of source bits to preserve, N, is encoded as a single
     byte unsigned integer following the 'ext' bytecode.

'zero_ext' (0x2a) N: A => A, zero-extended from N bits
     Pop an unsigned value from the stack; zero all but the bottom N
     bits.  This means that all bits to the left of bit N-1 (where the
     least significant bit is bit 0) are set to the value of bit N-1.

     The number of source bits to preserve, N, is encoded as a single
     byte unsigned integer following the 'zero_ext' bytecode.

'ref8' (0x17): ADDR => A
'ref16' (0x18): ADDR => A
'ref32' (0x19): ADDR => A
'ref64' (0x1a): ADDR => A
     Pop an address ADDR from the stack.  For bytecode 'ref'N, fetch an
     N-bit value from ADDR, using the natural target endianness.  Push
     the fetched value as an unsigned integer.

     Note that ADDR may not be aligned in any particular way; the 'refN'
     bytecodes should operate correctly for any address.

     If attempting to access memory at ADDR would cause a processor
     exception of some sort, terminate with an error.

'ref_float' (0x1b): ADDR => D
'ref_double' (0x1c): ADDR => D
'ref_long_double' (0x1d): ADDR => D
'l_to_d' (0x1e): A => D
'd_to_l' (0x1f): D => A
     Not implemented yet.

'dup' (0x28): A => A A
     Push another copy of the stack's top element.

'swap' (0x2b): A B => B A
     Exchange the top two items on the stack.

'pop' (0x29): A =>
     Discard the top value on the stack.

'pick' (0x32) N: A ... B => A ... B A
     Duplicate an item from the stack and push it on the top of the
     stack.  N, a single byte, indicates the stack item to copy.  If N
     is zero, this is the same as 'dup'; if N is one, it copies the item
     under the top item, etc.  If N exceeds the number of items on the
     stack, terminate with an error.

'rot' (0x33): A B C => C B A
     Rotate the top three items on the stack.

'if_goto' (0x20) OFFSET: A =>
     Pop an integer off the stack; if it is non-zero, branch to the
     given offset in the bytecode string.  Otherwise, continue to the
     next instruction in the bytecode stream.  In other words, if A is
     non-zero, set the 'pc' register to 'start' + OFFSET.  Thus, an
     offset of zero denotes the beginning of the expression.

     The OFFSET is stored as a sixteen-bit unsigned value, stored
     immediately following the 'if_goto' bytecode.  It is always stored
     most significant byte first, regardless of the target's normal
     endianness.  The offset is not guaranteed to fall at any particular
     alignment within the bytecode stream; thus, on machines where
     fetching a 16-bit on an unaligned address raises an exception, you
     should fetch the offset one byte at a time.

'goto' (0x21) OFFSET: =>
     Branch unconditionally to OFFSET; in other words, set the 'pc'
     register to 'start' + OFFSET.

     The offset is stored in the same way as for the 'if_goto' bytecode.

'const8' (0x22) N: => N
'const16' (0x23) N: => N
'const32' (0x24) N: => N
'const64' (0x25) N: => N
     Push the integer constant N on the stack, without sign extension.
     To produce a small negative value, push a small twos-complement
     value, and then sign-extend it using the 'ext' bytecode.

     The constant N is stored in the appropriate number of bytes
     following the 'const'B bytecode.  The constant N is always stored
     most significant byte first, regardless of the target's normal
     endianness.  The constant is not guaranteed to fall at any
     particular alignment within the bytecode stream; thus, on machines
     where fetching a 16-bit on an unaligned address raises an
     exception, you should fetch N one byte at a time.

'reg' (0x26) N: => A
     Push the value of register number N, without sign extension.  The
     registers are numbered following GDB's conventions.

     The register number N is encoded as a 16-bit unsigned integer
     immediately following the 'reg' bytecode.  It is always stored most
     significant byte first, regardless of the target's normal
     endianness.  The register number is not guaranteed to fall at any
     particular alignment within the bytecode stream; thus, on machines
     where fetching a 16-bit on an unaligned address raises an
     exception, you should fetch the register number one byte at a time.

'getv' (0x2c) N: => V
     Push the value of trace state variable number N, without sign
     extension.

     The variable number N is encoded as a 16-bit unsigned integer
     immediately following the 'getv' bytecode.  It is always stored
     most significant byte first, regardless of the target's normal
     endianness.  The variable number is not guaranteed to fall at any
     particular alignment within the bytecode stream; thus, on machines
     where fetching a 16-bit on an unaligned address raises an
     exception, you should fetch the register number one byte at a time.

'setv' (0x2d) N: => V
     Set trace state variable number N to the value found on the top of
     the stack.  The stack is unchanged, so that the value is readily
     available if the assignment is part of a larger expression.  The
     handling of N is as described for 'getv'.

'trace' (0x0c): ADDR SIZE =>
     Record the contents of the SIZE bytes at ADDR in a trace buffer,
     for later retrieval by GDB.

'trace_quick' (0x0d) SIZE: ADDR => ADDR
     Record the contents of the SIZE bytes at ADDR in a trace buffer,
     for later retrieval by GDB. SIZE is a single byte unsigned integer
     following the 'trace' opcode.

     This bytecode is equivalent to the sequence 'dup const8 SIZE
     trace', but we provide it anyway to save space in bytecode strings.

'trace16' (0x30) SIZE: ADDR => ADDR
     Identical to trace_quick, except that SIZE is a 16-bit big-endian
     unsigned integer, not a single byte.  This should probably have
     been named 'trace_quick16', for consistency.

'tracev' (0x2e) N: => A
     Record the value of trace state variable number N in the trace
     buffer.  The handling of N is as described for 'getv'.

'tracenz' (0x2f) ADDR SIZE =>
     Record the bytes at ADDR in a trace buffer, for later retrieval by
     GDB. Stop at either the first zero byte, or when SIZE bytes have
     been recorded, whichever occurs first.

'printf' (0x34) NUMARGS STRING =>
     Do a formatted print, in the style of the C function 'printf').
     The value of NUMARGS is the number of arguments to expect on the
     stack, while STRING is the format string, prefixed with a two-byte
     length.  The last byte of the string must be zero, and is included
     in the length.  The format string includes escaped sequences just
     as it appears in C source, so for instance the format string
     '"\t%d\n"' is six characters long, and the output will consist of a
     tab character, a decimal number, and a newline.  At the top of the
     stack, above the values to be printed, this bytecode will pop a
     "function" and "channel".  If the function is nonzero, then the
     target may treat it as a function and call it, passing the channel
     as a first argument, as with the C function 'fprintf'.  If the
     function is zero, then the target may simply call a standard
     formatted print function of its choice.  In all, this bytecode pops
     2 + NUMARGS stack elements, and pushes nothing.

'end' (0x27): =>
     Stop executing bytecode; the result should be the top element of
     the stack.  If the purpose of the expression was to compute an
     lvalue or a range of memory, then the next-to-top of the stack is
     the lvalue's address, and the top of the stack is the lvalue's
     size, in bytes.


File: gdb.info,  Node: Using Agent Expressions,  Next: Varying Target Capabilities,  Prev: Bytecode Descriptions,  Up: Agent Expressions

F.3 Using Agent Expressions
===========================

Agent expressions can be used in several different ways by GDB, and the
debugger can generate different bytecode sequences as appropriate.

   One possibility is to do expression evaluation on the target rather
than the host, such as for the conditional of a conditional tracepoint.
In such a case, GDB compiles the source expression into a bytecode
sequence that simply gets values from registers or memory, does
arithmetic, and returns a result.

   Another way to use agent expressions is for tracepoint data
collection.  GDB generates a different bytecode sequence for collection;
in addition to bytecodes that do the calculation, GDB adds 'trace'
bytecodes to save the pieces of memory that were used.

   * The user selects trace points in the program's code at which GDB
     should collect data.

   * The user specifies expressions to evaluate at each trace point.
     These expressions may denote objects in memory, in which case those
     objects' contents are recorded as the program runs, or computed
     values, in which case the values themselves are recorded.

   * GDB transmits the tracepoints and their associated expressions to
     the GDB agent, running on the debugging target.

   * The agent arranges to be notified when a trace point is hit.

   * When execution on the target reaches a trace point, the agent
     evaluates the expressions associated with that trace point, and
     records the resulting values and memory ranges.

   * Later, when the user selects a given trace event and inspects the
     objects and expression values recorded, GDB talks to the agent to
     retrieve recorded data as necessary to meet the user's requests.
     If the user asks to see an object whose contents have not been
     recorded, GDB reports an error.


File: gdb.info,  Node: Varying Target Capabilities,  Next: Rationale,  Prev: Using Agent Expressions,  Up: Agent Expressions

F.4 Varying Target Capabilities
===============================

Some targets don't support floating-point, and some would rather not
have to deal with 'long long' operations.  Also, different targets will
have different stack sizes, and different bytecode buffer lengths.

   Thus, GDB needs a way to ask the target about itself.  We haven't
worked out the details yet, but in general, GDB should be able to send
the target a packet asking it to describe itself.  The reply should be a
packet whose length is explicit, so we can add new information to the
packet in future revisions of the agent, without confusing old versions
of GDB, and it should contain a version number.  It should contain at
least the following information:

   * whether floating point is supported

   * whether 'long long' is supported

   * maximum acceptable size of bytecode stack

   * maximum acceptable length of bytecode expressions

   * which registers are actually available for collection

   * whether the target supports disabled tracepoints


File: gdb.info,  Node: Rationale,  Prev: Varying Target Capabilities,  Up: Agent Expressions

F.5 Rationale
=============

Some of the design decisions apparent above are arguable.

What about stack overflow/underflow?
     GDB should be able to query the target to discover its stack size.
     Given that information, GDB can determine at translation time
     whether a given expression will overflow the stack.  But this spec
     isn't about what kinds of error-checking GDB ought to do.

Why are you doing everything in LONGEST?

     Speed isn't important, but agent code size is; using LONGEST brings
     in a bunch of support code to do things like division, etc.  So
     this is a serious concern.

     First, note that you don't need different bytecodes for different
     operand sizes.  You can generate code without _knowing_ how big the
     stack elements actually are on the target.  If the target only
     supports 32-bit ints, and you don't send any 64-bit bytecodes,
     everything just works.  The observation here is that the MIPS and
     the Alpha have only fixed-size registers, and you can still get C's
     semantics even though most instructions only operate on full-sized
     words.  You just need to make sure everything is properly
     sign-extended at the right times.  So there is no need for 32- and
     64-bit variants of the bytecodes.  Just implement everything using
     the largest size you support.

     GDB should certainly check to see what sizes the target supports,
     so the user can get an error earlier, rather than later.  But this
     information is not necessary for correctness.

Why don't you have '>' or '<=' operators?
     I want to keep the interpreter small, and we don't need them.  We
     can combine the 'less_' opcodes with 'log_not', and swap the order
     of the operands, yielding all four asymmetrical comparison
     operators.  For example, '(x <= y)' is '! (x > y)', which is '! (y
     < x)'.

Why do you have 'log_not'?
Why do you have 'ext'?
Why do you have 'zero_ext'?
     These are all easily synthesized from other instructions, but I
     expect them to be used frequently, and they're simple, so I include
     them to keep bytecode strings short.

     'log_not' is equivalent to 'const8 0 equal'; it's used in half the
     relational operators.

     'ext N' is equivalent to 'const8 S-N lsh const8 S-N rsh_signed',
     where S is the size of the stack elements; it follows 'refM' and
     REG bytecodes when the value should be signed.  See the next
     bulleted item.

     'zero_ext N' is equivalent to 'constM MASK log_and'; it's used
     whenever we push the value of a register, because we can't assume
     the upper bits of the register aren't garbage.

Why not have sign-extending variants of the 'ref' operators?
     Because that would double the number of 'ref' operators, and we
     need the 'ext' bytecode anyway for accessing bitfields.

Why not have constant-address variants of the 'ref' operators?
     Because that would double the number of 'ref' operators again, and
     'const32 ADDRESS ref32' is only one byte longer.

Why do the 'refN' operators have to support unaligned fetches?
     GDB will generate bytecode that fetches multi-byte values at
     unaligned addresses whenever the executable's debugging information
     tells it to.  Furthermore, GDB does not know the value the pointer
     will have when GDB generates the bytecode, so it cannot determine
     whether a particular fetch will be aligned or not.

     In particular, structure bitfields may be several bytes long, but
     follow no alignment rules; members of packed structures are not
     necessarily aligned either.

     In general, there are many cases where unaligned references occur
     in correct C code, either at the programmer's explicit request, or
     at the compiler's discretion.  Thus, it is simpler to make the GDB
     agent bytecodes work correctly in all circumstances than to make
     GDB guess in each case whether the compiler did the usual thing.

Why are there no side-effecting operators?
     Because our current client doesn't want them?  That's a cheap
     answer.  I think the real answer is that I'm afraid of implementing
     function calls.  We should re-visit this issue after the present
     contract is delivered.

Why aren't the 'goto' ops PC-relative?
     The interpreter has the base address around anyway for PC bounds
     checking, and it seemed simpler.

Why is there only one offset size for the 'goto' ops?
     Offsets are currently sixteen bits.  I'm not happy with this
     situation either:

     Suppose we have multiple branch ops with different offset sizes.
     As I generate code left-to-right, all my jumps are forward jumps
     (there are no loops in expressions), so I never know the target
     when I emit the jump opcode.  Thus, I have to either always assume
     the largest offset size, or do jump relaxation on the code after I
     generate it, which seems like a big waste of time.

     I can imagine a reasonable expression being longer than 256 bytes.
     I can't imagine one being longer than 64k.  Thus, we need 16-bit
     offsets.  This kind of reasoning is so bogus, but relaxation is
     pathetic.

     The other approach would be to generate code right-to-left.  Then
     I'd always know my offset size.  That might be fun.

Where is the function call bytecode?

     When we add side-effects, we should add this.

Why does the 'reg' bytecode take a 16-bit register number?

     Intel's IA-64 architecture has 128 general-purpose registers, and
     128 floating-point registers, and I'm sure it has some random
     control registers.

Why do we need 'trace' and 'trace_quick'?
     Because GDB needs to record all the memory contents and registers
     an expression touches.  If the user wants to evaluate an expression
     'x->y->z', the agent must record the values of 'x' and 'x->y' as
     well as the value of 'x->y->z'.

Don't the 'trace' bytecodes make the interpreter less general?
     They do mean that the interpreter contains special-purpose code,
     but that doesn't mean the interpreter can only be used for that
     purpose.  If an expression doesn't use the 'trace' bytecodes, they
     don't get in its way.

Why doesn't 'trace_quick' consume its arguments the way everything else does?
     In general, you do want your operators to consume their arguments;
     it's consistent, and generally reduces the amount of stack
     rearrangement necessary.  However, 'trace_quick' is a kludge to
     save space; it only exists so we needn't write 'dup const8 SIZE
     trace' before every memory reference.  Therefore, it's okay for it
     not to consume its arguments; it's meant for a specific context in
     which we know exactly what it should do with the stack.  If we're
     going to have a kludge, it should be an effective kludge.

Why does 'trace16' exist?
     That opcode was added by the customer that contracted Cygnus for
     the data tracing work.  I personally think it is unnecessary;
     objects that large will be quite rare, so it is okay to use 'dup
     const16 SIZE trace' in those cases.

     Whatever we decide to do with 'trace16', we should at least leave
     opcode 0x30 reserved, to remain compatible with the customer who
     added it.


File: gdb.info,  Node: Target Descriptions,  Next: Operating System Information,  Prev: Agent Expressions,  Up: Top

Appendix G Target Descriptions
******************************

One of the challenges of using GDB to debug embedded systems is that
there are so many minor variants of each processor architecture in use.
It is common practice for vendors to start with a standard processor
core -- ARM, PowerPC, or MIPS, for example -- and then make changes to
adapt it to a particular market niche.  Some architectures have hundreds
of variants, available from dozens of vendors.  This leads to a number
of problems:

   * With so many different customized processors, it is difficult for
     the GDB maintainers to keep up with the changes.
   * Since individual variants may have short lifetimes or limited
     audiences, it may not be worthwhile to carry information about
     every variant in the GDB source tree.
   * When GDB does support the architecture of the embedded system at
     hand, the task of finding the correct architecture name to give the
     'set architecture' command can be error-prone.

   To address these problems, the GDB remote protocol allows a target
system to not only identify itself to GDB, but to actually describe its
own features.  This lets GDB support processor variants it has never
seen before -- to the extent that the descriptions are accurate, and
that GDB understands them.

   GDB must be linked with the Expat library to support XML target
descriptions.  *Note Expat::.

* Menu:

* Retrieving Descriptions::         How descriptions are fetched from a target.
* Target Description Format::       The contents of a target description.
* Predefined Target Types::         Standard types available for target
                                    descriptions.
* Standard Target Features::        Features GDB knows about.


File: gdb.info,  Node: Retrieving Descriptions,  Next: Target Description Format,  Up: Target Descriptions

G.1 Retrieving Descriptions
===========================

Target descriptions can be read from the target automatically, or
specified by the user manually.  The default behavior is to read the
description from the target.  GDB retrieves it via the remote protocol
using 'qXfer' requests (*note qXfer: General Query Packets.).  The ANNEX
in the 'qXfer' packet will be 'target.xml'.  The contents of the
'target.xml' annex are an XML document, of the form described in *note
Target Description Format::.

   Alternatively, you can specify a file to read for the target
description.  If a file is set, the target will not be queried.  The
commands to specify a file are:

'set tdesc filename PATH'
     Read the target description from PATH.

'unset tdesc filename'
     Do not read the XML target description from a file.  GDB will use
     the description supplied by the current target.

'show tdesc filename'
     Show the filename to read for a target description, if any.


File: gdb.info,  Node: Target Description Format,  Next: Predefined Target Types,  Prev: Retrieving Descriptions,  Up: Target Descriptions

G.2 Target Description Format
=============================

A target description annex is an XML (http://www.w3.org/XML/) document
which complies with the Document Type Definition provided in the GDB
sources in 'gdb/features/gdb-target.dtd'.  This means you can use
generally available tools like 'xmllint' to check that your feature
descriptions are well-formed and valid.  However, to help people
unfamiliar with XML write descriptions for their targets, we also
describe the grammar here.

   Target descriptions can identify the architecture of the remote
target and (for some architectures) provide information about custom
register sets.  They can also identify the OS ABI of the remote target.
GDB can use this information to autoconfigure for your target, or to
warn you if you connect to an unsupported target.

   Here is a simple target description:

     <target version="1.0">
       <architecture>i386:x86-64</architecture>
     </target>

This minimal description only says that the target uses the x86-64
architecture.

   A target description has the following overall form, with [ ] marking
optional elements and ... marking repeatable elements.  The elements are
explained further below.

     <?xml version="1.0"?>
     <!DOCTYPE target SYSTEM "gdb-target.dtd">
     <target version="1.0">
       [ARCHITECTURE]
       [OSABI]
       [COMPATIBLE]
       [FEATURE...]
     </target>

The description is generally insensitive to whitespace and line breaks,
under the usual common-sense rules.  The XML version declaration and
document type declaration can generally be omitted (GDB does not require
them), but specifying them may be useful for XML validation tools.  The
'version' attribute for '<target>' may also be omitted, but we recommend
including it; if future versions of GDB use an incompatible revision of
'gdb-target.dtd', they will detect and report the version mismatch.

G.2.1 Inclusion
---------------

It can sometimes be valuable to split a target description up into
several different annexes, either for organizational purposes, or to
share files between different possible target descriptions.  You can
divide a description into multiple files by replacing any element of the
target description with an inclusion directive of the form:

     <xi:include href="DOCUMENT"/>

When GDB encounters an element of this form, it will retrieve the named
XML DOCUMENT, and replace the inclusion directive with the contents of
that document.  If the current description was read using 'qXfer', then
so will be the included document; DOCUMENT will be interpreted as the
name of an annex.  If the current description was read from a file, GDB
will look for DOCUMENT as a file in the same directory where it found
the original description.

G.2.2 Architecture
------------------

An '<architecture>' element has this form:

       <architecture>ARCH</architecture>

   ARCH is one of the architectures from the set accepted by 'set
architecture' (*note Specifying a Debugging Target: Targets.).

G.2.3 OS ABI
------------

This optional field was introduced in GDB version 7.0.  Previous
versions of GDB ignore it.

   An '<osabi>' element has this form:

       <osabi>ABI-NAME</osabi>

   ABI-NAME is an OS ABI name from the same selection accepted by 'set osabi'
(*note Configuring the Current ABI: ABI.).

G.2.4 Compatible Architecture
-----------------------------

This optional field was introduced in GDB version 7.0.  Previous
versions of GDB ignore it.

   A '<compatible>' element has this form:

       <compatible>ARCH</compatible>

   ARCH is one of the architectures from the set accepted by 'set
architecture' (*note Specifying a Debugging Target: Targets.).

   A '<compatible>' element is used to specify that the target is able
to run binaries in some other than the main target architecture given by
the '<architecture>' element.  For example, on the Cell Broadband
Engine, the main architecture is 'powerpc:common' or 'powerpc:common64',
but the system is able to run binaries in the 'spu' architecture as
well.  The way to describe this capability with '<compatible>' is as
follows:

       <architecture>powerpc:common</architecture>
       <compatible>spu</compatible>

G.2.5 Features
--------------

Each '<feature>' describes some logical portion of the target system.
Features are currently used to describe available CPU registers and the
types of their contents.  A '<feature>' element has this form:

     <feature name="NAME">
       [TYPE...]
       REG...
     </feature>

Each feature's name should be unique within the description.  The name
of a feature does not matter unless GDB has some special knowledge of
the contents of that feature; if it does, the feature should have its
standard name.  *Note Standard Target Features::.

G.2.6 Types
-----------

Any register's value is a collection of bits which GDB must interpret.
The default interpretation is a two's complement integer, but other
types can be requested by name in the register description.  Some
predefined types are provided by GDB (*note Predefined Target Types::),
and the description can define additional composite types.

   Each type element must have an 'id' attribute, which gives a unique
(within the containing '<feature>') name to the type.  Types must be
defined before they are used.

   Some targets offer vector registers, which can be treated as arrays
of scalar elements.  These types are written as '<vector>' elements,
specifying the array element type, TYPE, and the number of elements,
COUNT:

     <vector id="ID" type="TYPE" count="COUNT"/>

   If a register's value is usefully viewed in multiple ways, define it
with a union type containing the useful representations.  The '<union>'
element contains one or more '<field>' elements, each of which has a
NAME and a TYPE:

     <union id="ID">
       <field name="NAME" type="TYPE"/>
       ...
     </union>

   If a register's value is composed from several separate values,
define it with a structure type.  There are two forms of the '<struct>'
element; a '<struct>' element must either contain only bitfields or
contain no bitfields.  If the structure contains only bitfields, its
total size in bytes must be specified, each bitfield must have an
explicit start and end, and bitfields are automatically assigned an
integer type.  The field's START should be less than or equal to its
END, and zero represents the least significant bit.

     <struct id="ID" size="SIZE">
       <field name="NAME" start="START" end="END"/>
       ...
     </struct>

   If the structure contains no bitfields, then each field has an
explicit type, and no implicit padding is added.

     <struct id="ID">
       <field name="NAME" type="TYPE"/>
       ...
     </struct>

   If a register's value is a series of single-bit flags, define it with
a flags type.  The '<flags>' element has an explicit SIZE and contains
one or more '<field>' elements.  Each field has a NAME, a START, and an
END.  Only single-bit flags are supported.

     <flags id="ID" size="SIZE">
       <field name="NAME" start="START" end="END"/>
       ...
     </flags>

G.2.7 Registers
---------------

Each register is represented as an element with this form:

     <reg name="NAME"
          bitsize="SIZE"
          [regnum="NUM"]
          [save-restore="SAVE-RESTORE"]
          [type="TYPE"]
          [group="GROUP"]/>

The components are as follows:

NAME
     The register's name; it must be unique within the target
     description.

BITSIZE
     The register's size, in bits.

REGNUM
     The register's number.  If omitted, a register's number is one
     greater than that of the previous register (either in the current
     feature or in a preceding feature); the first register in the
     target description defaults to zero.  This register number is used
     to read or write the register; e.g. it is used in the remote 'p'
     and 'P' packets, and registers appear in the 'g' and 'G' packets in
     order of increasing register number.

SAVE-RESTORE
     Whether the register should be preserved across inferior function
     calls; this must be either 'yes' or 'no'.  The default is 'yes',
     which is appropriate for most registers except for some system
     control registers; this is not related to the target's ABI.

TYPE
     The type of the register.  It may be a predefined type, a type
     defined in the current feature, or one of the special types 'int'
     and 'float'.  'int' is an integer type of the correct size for
     BITSIZE, and 'float' is a floating point type (in the
     architecture's normal floating point format) of the correct size
     for BITSIZE.  The default is 'int'.

GROUP
     The register group to which this register belongs.  It must be
     either 'general', 'float', or 'vector'.  If no GROUP is specified,
     GDB will not display the register in 'info registers'.


File: gdb.info,  Node: Predefined Target Types,  Next: Standard Target Features,  Prev: Target Description Format,  Up: Target Descriptions

G.3 Predefined Target Types
===========================

Type definitions in the self-description can build up composite types
from basic building blocks, but can not define fundamental types.
Instead, standard identifiers are provided by GDB for the fundamental
types.  The currently supported types are:

'int8'
'int16'
'int32'
'int64'
'int128'
     Signed integer types holding the specified number of bits.

'uint8'
'uint16'
'uint32'
'uint64'
'uint128'
     Unsigned integer types holding the specified number of bits.

'code_ptr'
'data_ptr'
     Pointers to unspecified code and data.  The program counter and any
     dedicated return address register may be marked as code pointers;
     printing a code pointer converts it into a symbolic address.  The
     stack pointer and any dedicated address registers may be marked as
     data pointers.

'ieee_single'
     Single precision IEEE floating point.

'ieee_double'
     Double precision IEEE floating point.

'arm_fpa_ext'
     The 12-byte extended precision format used by ARM FPA registers.

'i387_ext'
     The 10-byte extended precision format used by x87 registers.

'i386_eflags'
     32bit EFLAGS register used by x86.

'i386_mxcsr'
     32bit MXCSR register used by x86.


File: gdb.info,  Node: Standard Target Features,  Prev: Predefined Target Types,  Up: Target Descriptions

G.4 Standard Target Features
============================

A target description must contain either no registers or all the
target's registers.  If the description contains no registers, then GDB
will assume a default register layout, selected based on the
architecture.  If the description contains any registers, the default
layout will not be used; the standard registers must be described in the
target description, in such a way that GDB can recognize them.

   This is accomplished by giving specific names to feature elements
which contain standard registers.  GDB will look for features with those
names and verify that they contain the expected registers; if any known
feature is missing required registers, or if any required feature is
missing, GDB will reject the target description.  You can add additional
registers to any of the standard features -- GDB will display them just
as if they were added to an unrecognized feature.

   This section lists the known features and their expected contents.
Sample XML documents for these features are included in the GDB source
tree, in the directory 'gdb/features'.

   Names recognized by GDB should include the name of the company or
organization which selected the name, and the overall architecture to
which the feature applies; so e.g. the feature containing ARM core
registers is named 'org.gnu.gdb.arm.core'.

   The names of registers are not case sensitive for the purpose of
recognizing standard features, but GDB will only display registers using
the capitalization used in the description.

* Menu:

* AArch64 Features::
* ARM Features::
* i386 Features::
* MIPS Features::
* M68K Features::
* Nios II Features::
* PowerPC Features::
* S/390 and System z Features::
* TIC6x Features::


File: gdb.info,  Node: AArch64 Features,  Next: ARM Features,  Up: Standard Target Features

G.4.1 AArch64 Features
----------------------

The 'org.gnu.gdb.aarch64.core' feature is required for AArch64 targets.
It should contain registers 'x0' through 'x30', 'sp', 'pc', and 'cpsr'.

   The 'org.gnu.gdb.aarch64.fpu' feature is optional.  If present, it
should contain registers 'v0' through 'v31', 'fpsr', and 'fpcr'.


File: gdb.info,  Node: ARM Features,  Next: i386 Features,  Prev: AArch64 Features,  Up: Standard Target Features

G.4.2 ARM Features
------------------

The 'org.gnu.gdb.arm.core' feature is required for non-M-profile ARM
targets.  It should contain registers 'r0' through 'r13', 'sp', 'lr',
'pc', and 'cpsr'.

   For M-profile targets (e.g.  Cortex-M3), the 'org.gnu.gdb.arm.core'
feature is replaced by 'org.gnu.gdb.arm.m-profile'.  It should contain
registers 'r0' through 'r13', 'sp', 'lr', 'pc', and 'xpsr'.

   The 'org.gnu.gdb.arm.fpa' feature is optional.  If present, it should
contain registers 'f0' through 'f7' and 'fps'.

   The 'org.gnu.gdb.xscale.iwmmxt' feature is optional.  If present, it
should contain at least registers 'wR0' through 'wR15' and 'wCGR0'
through 'wCGR3'.  The 'wCID', 'wCon', 'wCSSF', and 'wCASF' registers are
optional.

   The 'org.gnu.gdb.arm.vfp' feature is optional.  If present, it should
contain at least registers 'd0' through 'd15'.  If they are present,
'd16' through 'd31' should also be included.  GDB will synthesize the
single-precision registers from halves of the double-precision
registers.

   The 'org.gnu.gdb.arm.neon' feature is optional.  It does not need to
contain registers; it instructs GDB to display the VFP double-precision
registers as vectors and to synthesize the quad-precision registers from
pairs of double-precision registers.  If this feature is present,
'org.gnu.gdb.arm.vfp' must also be present and include 32
double-precision registers.


File: gdb.info,  Node: i386 Features,  Next: MIPS Features,  Prev: ARM Features,  Up: Standard Target Features

G.4.3 i386 Features
-------------------

The 'org.gnu.gdb.i386.core' feature is required for i386/amd64 targets.
It should describe the following registers:

   - 'eax' through 'edi' plus 'eip' for i386
   - 'rax' through 'r15' plus 'rip' for amd64
   - 'eflags', 'cs', 'ss', 'ds', 'es', 'fs', 'gs'
   - 'st0' through 'st7'
   - 'fctrl', 'fstat', 'ftag', 'fiseg', 'fioff', 'foseg', 'fooff' and
     'fop'

   The register sets may be different, depending on the target.

   The 'org.gnu.gdb.i386.sse' feature is optional.  It should describe
registers:

   - 'xmm0' through 'xmm7' for i386
   - 'xmm0' through 'xmm15' for amd64
   - 'mxcsr'

   The 'org.gnu.gdb.i386.avx' feature is optional and requires the
'org.gnu.gdb.i386.sse' feature.  It should describe the upper 128 bits
of YMM registers:

   - 'ymm0h' through 'ymm7h' for i386
   - 'ymm0h' through 'ymm15h' for amd64

   The 'org.gnu.gdb.i386.mpx' is an optional feature representing
Intel(R) Memory Protection Extension (MPX). It should describe the
following registers:

   - 'bnd0raw' through 'bnd3raw' for i386 and amd64.
   - 'bndcfgu' and 'bndstatus' for i386 and amd64.

   The 'org.gnu.gdb.i386.linux' feature is optional.  It should describe
a single register, 'orig_eax'.

   The 'org.gnu.gdb.i386.avx512' feature is optional and requires the
'org.gnu.gdb.i386.avx' feature.  It should describe additional XMM
registers:

   - 'xmm16h' through 'xmm31h', only valid for amd64.

   It should describe the upper 128 bits of additional YMM registers:

   - 'ymm16h' through 'ymm31h', only valid for amd64.

   It should describe the upper 256 bits of ZMM registers:

   - 'zmm0h' through 'zmm7h' for i386.
   - 'zmm0h' through 'zmm15h' for amd64.

   It should describe the additional ZMM registers:

   - 'zmm16h' through 'zmm31h', only valid for amd64.


File: gdb.info,  Node: MIPS Features,  Next: M68K Features,  Prev: i386 Features,  Up: Standard Target Features

G.4.4 MIPS Features
-------------------

The 'org.gnu.gdb.mips.cpu' feature is required for MIPS targets.  It
should contain registers 'r0' through 'r31', 'lo', 'hi', and 'pc'.  They
may be 32-bit or 64-bit depending on the target.

   The 'org.gnu.gdb.mips.cp0' feature is also required.  It should
contain at least the 'status', 'badvaddr', and 'cause' registers.  They
may be 32-bit or 64-bit depending on the target.

   The 'org.gnu.gdb.mips.fpu' feature is currently required, though it
may be optional in a future version of GDB.  It should contain registers
'f0' through 'f31', 'fcsr', and 'fir'.  They may be 32-bit or 64-bit
depending on the target.

   The 'org.gnu.gdb.mips.dsp' feature is optional.  It should contain
registers 'hi1' through 'hi3', 'lo1' through 'lo3', and 'dspctl'.  The
'dspctl' register should be 32-bit and the rest may be 32-bit or 64-bit
depending on the target.

   The 'org.gnu.gdb.mips.linux' feature is optional.  It should contain
a single register, 'restart', which is used by the Linux kernel to
control restartable syscalls.


File: gdb.info,  Node: M68K Features,  Next: Nios II Features,  Prev: MIPS Features,  Up: Standard Target Features

G.4.5 M68K Features
-------------------

''org.gnu.gdb.m68k.core''
''org.gnu.gdb.coldfire.core''
''org.gnu.gdb.fido.core''
     One of those features must be always present.  The feature that is
     present determines which flavor of m68k is used.  The feature that
     is present should contain registers 'd0' through 'd7', 'a0' through
     'a5', 'fp', 'sp', 'ps' and 'pc'.

''org.gnu.gdb.coldfire.fp''
     This feature is optional.  If present, it should contain registers
     'fp0' through 'fp7', 'fpcontrol', 'fpstatus' and 'fpiaddr'.


File: gdb.info,  Node: Nios II Features,  Next: PowerPC Features,  Prev: M68K Features,  Up: Standard Target Features

G.4.6 Nios II Features
----------------------

The 'org.gnu.gdb.nios2.cpu' feature is required for Nios II targets.  It
should contain the 32 core registers ('zero', 'at', 'r2' through 'r23',
'et' through 'ra'), 'pc', and the 16 control registers ('status' through
'mpuacc').


File: gdb.info,  Node: PowerPC Features,  Next: S/390 and System z Features,  Prev: Nios II Features,  Up: Standard Target Features

G.4.7 PowerPC Features
----------------------

The 'org.gnu.gdb.power.core' feature is required for PowerPC targets.
It should contain registers 'r0' through 'r31', 'pc', 'msr', 'cr', 'lr',
'ctr', and 'xer'.  They may be 32-bit or 64-bit depending on the target.

   The 'org.gnu.gdb.power.fpu' feature is optional.  It should contain
registers 'f0' through 'f31' and 'fpscr'.

   The 'org.gnu.gdb.power.altivec' feature is optional.  It should
contain registers 'vr0' through 'vr31', 'vscr', and 'vrsave'.

   The 'org.gnu.gdb.power.vsx' feature is optional.  It should contain
registers 'vs0h' through 'vs31h'.  GDB will combine these registers with
the floating point registers ('f0' through 'f31') and the altivec
registers ('vr0' through 'vr31') to present the 128-bit wide registers
'vs0' through 'vs63', the set of vector registers for POWER7.

   The 'org.gnu.gdb.power.spe' feature is optional.  It should contain
registers 'ev0h' through 'ev31h', 'acc', and 'spefscr'.  SPE targets
should provide 32-bit registers in 'org.gnu.gdb.power.core' and provide
the upper halves in 'ev0h' through 'ev31h'.  GDB will combine these to
present registers 'ev0' through 'ev31' to the user.


File: gdb.info,  Node: S/390 and System z Features,  Next: TIC6x Features,  Prev: PowerPC Features,  Up: Standard Target Features

G.4.8 S/390 and System z Features
---------------------------------

The 'org.gnu.gdb.s390.core' feature is required for S/390 and System z
targets.  It should contain the PSW and the 16 general registers.  In
particular, System z targets should provide the 64-bit registers 'pswm',
'pswa', and 'r0' through 'r15'.  S/390 targets should provide the 32-bit
versions of these registers.  A System z target that runs in 31-bit
addressing mode should provide 32-bit versions of 'pswm' and 'pswa', as
well as the general register's upper halves 'r0h' through 'r15h', and
their lower halves 'r0l' through 'r15l'.

   The 'org.gnu.gdb.s390.fpr' feature is required.  It should contain
the 64-bit registers 'f0' through 'f15', and 'fpc'.

   The 'org.gnu.gdb.s390.acr' feature is required.  It should contain
the 32-bit registers 'acr0' through 'acr15'.

   The 'org.gnu.gdb.s390.linux' feature is optional.  It should contain
the register 'orig_r2', which is 64-bit wide on System z targets and
32-bit otherwise.  In addition, the feature may contain the 'last_break'
register, whose width depends on the addressing mode, as well as the
'system_call' register, which is always 32-bit wide.

   The 'org.gnu.gdb.s390.tdb' feature is optional.  It should contain
the 64-bit registers 'tdb0', 'tac', 'tct', 'atia', and 'tr0' through
'tr15'.


File: gdb.info,  Node: TIC6x Features,  Prev: S/390 and System z Features,  Up: Standard Target Features

G.4.9 TMS320C6x Features
------------------------

The 'org.gnu.gdb.tic6x.core' feature is required for TMS320C6x targets.
It should contain registers 'A0' through 'A15', registers 'B0' through
'B15', 'CSR' and 'PC'.

   The 'org.gnu.gdb.tic6x.gp' feature is optional.  It should contain
registers 'A16' through 'A31' and 'B16' through 'B31'.

   The 'org.gnu.gdb.tic6x.c6xp' feature is optional.  It should contain
registers 'TSR', 'ILC' and 'RILC'.


File: gdb.info,  Node: Operating System Information,  Next: Trace File Format,  Prev: Target Descriptions,  Up: Top

Appendix H Operating System Information
***************************************

* Menu:

* Process list::

Users of GDB often wish to obtain information about the state of the
operating system running on the target--for example the list of
processes, or the list of open files.  This section describes the
mechanism that makes it possible.  This mechanism is similar to the
target features mechanism (*note Target Descriptions::), but focuses on
a different aspect of target.

   Operating system information is retrived from the target via the
remote protocol, using 'qXfer' requests (*note qXfer osdata read::).
The object name in the request should be 'osdata', and the ANNEX
identifies the data to be fetched.


File: gdb.info,  Node: Process list,  Up: Operating System Information

H.1 Process list
================

When requesting the process list, the ANNEX field in the 'qXfer' request
should be 'processes'.  The returned data is an XML document.  The
formal syntax of this document is defined in 'gdb/features/osdata.dtd'.

   An example document is:

     <?xml version="1.0"?>
     <!DOCTYPE target SYSTEM "osdata.dtd">
     <osdata type="processes">
       <item>
         <column name="pid">1</column>
         <column name="user">root</column>
         <column name="command">/sbin/init</column>
         <column name="cores">1,2,3</column>
       </item>
     </osdata>

   Each item should include a column whose name is 'pid'.  The value of
that column should identify the process on the target.  The 'user' and
'command' columns are optional, and will be displayed by GDB.  The
'cores' column, if present, should contain a comma-separated list of
cores that this process is running on.  Target may provide additional
columns, which GDB currently ignores.


File: gdb.info,  Node: Trace File Format,  Next: Index Section Format,  Prev: Operating System Information,  Up: Top

Appendix I Trace File Format
****************************

The trace file comes in three parts: a header, a textual description
section, and a trace frame section with binary data.

   The header has the form '\x7fTRACE0\n'.  The first byte is '0x7f' so
as to indicate that the file contains binary data, while the '0' is a
version number that may have different values in the future.

   The description section consists of multiple lines of ASCII text
separated by newline characters ('0xa').  The lines may include a
variety of optional descriptive or context-setting information, such as
tracepoint definitions or register set size.  GDB will ignore any line
that it does not recognize.  An empty line marks the end of this
section.

   The trace frame section consists of a number of consecutive frames.
Each frame begins with a two-byte tracepoint number, followed by a
four-byte size giving the amount of data in the frame.  The data in the
frame consists of a number of blocks, each introduced by a character
indicating its type (at least register, memory, and trace state
variable).  The data in this section is raw binary, not a hexadecimal or
other encoding; its endianness matches the target's endianness.

'R BYTES'
     Register block.  The number and ordering of bytes matches that of a
     'g' packet in the remote protocol.  Note that these are the actual
     bytes, in target order and GDB register order, not a hexadecimal
     encoding.

'M ADDRESS LENGTH BYTES...'
     Memory block.  This is a contiguous block of memory, at the 8-byte
     address ADDRESS, with a 2-byte length LENGTH, followed by LENGTH
     bytes.

'V NUMBER VALUE'
     Trace state variable block.  This records the 8-byte signed value
     VALUE of trace state variable numbered NUMBER.

   Future enhancements of the trace file format may include additional
types of blocks.


File: gdb.info,  Node: Index Section Format,  Next: Man Pages,  Prev: Trace File Format,  Up: Top

Appendix J '.gdb_index' section format
**************************************

This section documents the index section that is created by 'save
gdb-index' (*note Index Files::).  The index section is DWARF-specific;
some knowledge of DWARF is assumed in this description.

   The mapped index file format is designed to be directly 'mmap'able on
any architecture.  In most cases, a datum is represented using a
little-endian 32-bit integer value, called an 'offset_type'.  Big endian
machines must byte-swap the values before using them.  Exceptions to
this rule are noted.  The data is laid out such that alignment is always
respected.

   A mapped index consists of several areas, laid out in order.

  1. The file header.  This is a sequence of values, of 'offset_type'
     unless otherwise noted:

       1. The version number, currently 8.  Versions 1, 2 and 3 are
          obsolete.  Version 4 uses a different hashing function from
          versions 5 and 6.  Version 6 includes symbols for inlined
          functions, whereas versions 4 and 5 do not.  Version 7 adds
          attributes to the CU indices in the symbol table.  Version 8
          specifies that symbols from DWARF type units
          ('DW_TAG_type_unit') refer to the type unit's symbol table and
          not the compilation unit ('DW_TAG_comp_unit') using the type.

          GDB will only read version 4, 5, or 6 indices by specifying
          'set use-deprecated-index-sections on'.  GDB has a workaround
          for potentially broken version 7 indices so it is currently
          not flagged as deprecated.

       2. The offset, from the start of the file, of the CU list.

       3. The offset, from the start of the file, of the types CU list.
          Note that this area can be empty, in which case this offset
          will be equal to the next offset.

       4. The offset, from the start of the file, of the address area.

       5. The offset, from the start of the file, of the symbol table.

       6. The offset, from the start of the file, of the constant pool.

  2. The CU list.  This is a sequence of pairs of 64-bit little-endian
     values, sorted by the CU offset.  The first element in each pair is
     the offset of a CU in the '.debug_info' section.  The second
     element in each pair is the length of that CU. References to a CU
     elsewhere in the map are done using a CU index, which is just the
     0-based index into this table.  Note that if there are type CUs,
     then conceptually CUs and type CUs form a single list for the
     purposes of CU indices.

  3. The types CU list.  This is a sequence of triplets of 64-bit
     little-endian values.  In a triplet, the first value is the CU
     offset, the second value is the type offset in the CU, and the
     third value is the type signature.  The types CU list is not
     sorted.

  4. The address area.  The address area consists of a sequence of
     address entries.  Each address entry has three elements:

       1. The low address.  This is a 64-bit little-endian value.

       2. The high address.  This is a 64-bit little-endian value.  Like
          'DW_AT_high_pc', the value is one byte beyond the end.

       3. The CU index.  This is an 'offset_type' value.

  5. The symbol table.  This is an open-addressed hash table.  The size
     of the hash table is always a power of 2.

     Each slot in the hash table consists of a pair of 'offset_type'
     values.  The first value is the offset of the symbol's name in the
     constant pool.  The second value is the offset of the CU vector in
     the constant pool.

     If both values are 0, then this slot in the hash table is empty.
     This is ok because while 0 is a valid constant pool index, it
     cannot be a valid index for both a string and a CU vector.

     The hash value for a table entry is computed by applying an
     iterative hash function to the symbol's name.  Starting with an
     initial value of 'r = 0', each (unsigned) character 'c' in the
     string is incorporated into the hash using the formula depending on
     the index version:

     Version 4
          The formula is 'r = r * 67 + c - 113'.

     Versions 5 to 7
          The formula is 'r = r * 67 + tolower (c) - 113'.

     The terminating '\0' is not incorporated into the hash.

     The step size used in the hash table is computed via '((hash * 17)
     & (size - 1)) | 1', where 'hash' is the hash value, and 'size' is
     the size of the hash table.  The step size is used to find the next
     candidate slot when handling a hash collision.

     The names of C++ symbols in the hash table are canonicalized.  We
     don't currently have a simple description of the canonicalization
     algorithm; if you intend to create new index sections, you must
     read the code.

  6. The constant pool.  This is simply a bunch of bytes.  It is
     organized so that alignment is correct: CU vectors are stored
     first, followed by strings.

     A CU vector in the constant pool is a sequence of 'offset_type'
     values.  The first value is the number of CU indices in the vector.
     Each subsequent value is the index and symbol attributes of a CU in
     the CU list.  This element in the hash table is used to indicate
     which CUs define the symbol and how the symbol is used.  See below
     for the format of each CU index+attributes entry.

     A string in the constant pool is zero-terminated.

   Attributes were added to CU index values in '.gdb_index' version 7.
If a symbol has multiple uses within a CU then there is one CU
index+attributes value for each use.

   The format of each CU index+attributes entry is as follows (bit 0 =
LSB):

Bits 0-23
     This is the index of the CU in the CU list.
Bits 24-27
     These bits are reserved for future purposes and must be zero.
Bits 28-30
     The kind of the symbol in the CU.

     0
          This value is reserved and should not be used.  By reserving
          zero the full 'offset_type' value is backwards compatible with
          previous versions of the index.
     1
          The symbol is a type.
     2
          The symbol is a variable or an enum value.
     3
          The symbol is a function.
     4
          Any other kind of symbol.
     5,6,7
          These values are reserved.

Bit 31
     This bit is zero if the value is global and one if it is static.

     The determination of whether a symbol is global or static is
     complicated.  The authorative reference is the file 'dwarf2read.c'
     in GDB sources.

   This pseudo-code describes the computation of a symbol's kind and
global/static attributes in the index.

     is_external = get_attribute (die, DW_AT_external);
     language = get_attribute (cu_die, DW_AT_language);
     switch (die->tag)
       {
       case DW_TAG_typedef:
       case DW_TAG_base_type:
       case DW_TAG_subrange_type:
         kind = TYPE;
         is_static = 1;
         break;
       case DW_TAG_enumerator:
         kind = VARIABLE;
         is_static = (language != CPLUS && language != JAVA);
         break;
       case DW_TAG_subprogram:
         kind = FUNCTION;
         is_static = ! (is_external || language == ADA);
         break;
       case DW_TAG_constant:
         kind = VARIABLE;
         is_static = ! is_external;
         break;
       case DW_TAG_variable:
         kind = VARIABLE;
         is_static = ! is_external;
         break;
       case DW_TAG_namespace:
         kind = TYPE;
         is_static = 0;
         break;
       case DW_TAG_class_type:
       case DW_TAG_interface_type:
       case DW_TAG_structure_type:
       case DW_TAG_union_type:
       case DW_TAG_enumeration_type:
         kind = TYPE;
         is_static = (language != CPLUS && language != JAVA);
         break;
       default:
         assert (0);
       }


File: gdb.info,  Node: Man Pages,  Next: Copying,  Prev: Index Section Format,  Up: Top

Appendix K Manual pages
***********************

* Menu:

* gdb man::                     The GNU Debugger man page
* gdbserver man::               Remote Server for the GNU Debugger man page
* gcore man::                   Generate a core file of a running program
* gdbinit man::                 gdbinit scripts


File: gdb.info,  Node: gdb man,  Next: gdbserver man,  Up: Man Pages

gdb man
=======

gdb ['-help'] ['-nh'] ['-nx'] ['-q'] ['-batch'] ['-cd='DIR] ['-f']
['-b' BPS] ['-tty='DEV] ['-s' SYMFILE] ['-e' PROG] ['-se' PROG]
['-c' CORE] ['-p' PROCID] ['-x' CMDS] ['-d' DIR] [PROG|PROG PROCID|PROG
CORE]

   The purpose of a debugger such as GDB is to allow you to see what is
going on "inside" another program while it executes - or what another
program was doing at the moment it crashed.

   GDB can do four main kinds of things (plus other things in support of
these) to help you catch bugs in the act:

   * Start your program, specifying anything that might affect its
     behavior.

   * Make your program stop on specified conditions.

   * Examine what has happened, when your program has stopped.

   * Change things in your program, so you can experiment with
     correcting the effects of one bug and go on to learn about another.

   You can use GDB to debug programs written in C, C++, Fortran and
Modula-2.

   GDB is invoked with the shell command 'gdb'.  Once started, it reads
commands from the terminal until you tell it to exit with the GDB
command 'quit'.  You can get online help from GDB itself by using the
command 'help'.

   You can run 'gdb' with no arguments or options; but the most usual
way to start GDB is with one argument or two, specifying an executable
program as the argument:

     gdb program

   You can also start with both an executable program and a core file
specified:

     gdb program core

   You can, instead, specify a process ID as a second argument, if you
want to debug a running process:

     gdb program 1234
     gdb -p 1234

would attach GDB to process '1234' (unless you also have a file named
'1234'; GDB does check for a core file first).  With option '-p' you can
omit the PROGRAM filename.

   Here are some of the most frequently needed GDB commands:

'break [FILE:]FUNCTIOP'
     Set a breakpoint at FUNCTION (in FILE).

'run [ARGLIST]'
     Start your program (with ARGLIST, if specified).

'bt'
     Backtrace: display the program stack.

'print EXPR'
     Display the value of an expression.

'c'
     Continue running your program (after stopping, e.g.  at a
     breakpoint).

'next'
     Execute next program line (after stopping); step _over_ any
     function calls in the line.

'edit [FILE:]FUNCTION'
     look at the program line where it is presently stopped.

'list [FILE:]FUNCTION'
     type the text of the program in the vicinity of where it is
     presently stopped.

'step'
     Execute next program line (after stopping); step _into_ any
     function calls in the line.

'help [NAME]'
     Show information about GDB command NAME, or general information
     about using GDB.

'quit'
     Exit from GDB.

   Any arguments other than options specify an executable file and core
file (or process ID); that is, the first argument encountered with no
associated option flag is equivalent to a '-se' option, and the second,
if any, is equivalent to a '-c' option if it's the name of a file.  Many
options have both long and short forms; both are shown here.  The long
forms are also recognized if you truncate them, so long as enough of the
option is present to be unambiguous.  (If you prefer, you can flag
option arguments with '+' rather than '-', though we illustrate the more
usual convention.)

   All the options and command line arguments you give are processed in
sequential order.  The order makes a difference when the '-x' option is
used.

'-help'
'-h'
     List all options, with brief explanations.

'-symbols=FILE'
'-s FILE'
     Read symbol table from file FILE.

'-write'
     Enable writing into executable and core files.

'-exec=FILE'
'-e FILE'
     Use file FILE as the executable file to execute when appropriate,
     and for examining pure data in conjunction with a core dump.

'-se=FILE'
     Read symbol table from file FILE and use it as the executable file.

'-core=FILE'
'-c FILE'
     Use file FILE as a core dump to examine.

'-command=FILE'
'-x FILE'
     Execute GDB commands from file FILE.

'-ex COMMAND'
     Execute given GDB COMMAND.

'-directory=DIRECTORY'
'-d DIRECTORY'
     Add DIRECTORY to the path to search for source files.

'-nh'
     Do not execute commands from '~/.gdbinit'.

'-nx'
'-n'
     Do not execute commands from any '.gdbinit' initialization files.

'-quiet'
'-q'
     "Quiet".  Do not print the introductory and copyright messages.
     These messages are also suppressed in batch mode.

'-batch'
     Run in batch mode.  Exit with status '0' after processing all the
     command files specified with '-x' (and '.gdbinit', if not
     inhibited).  Exit with nonzero status if an error occurs in
     executing the GDB commands in the command files.

     Batch mode may be useful for running GDB as a filter, for example
     to download and run a program on another computer; in order to make
     this more useful, the message

          Program exited normally.

     (which is ordinarily issued whenever a program running under GDB
     control terminates) is not issued when running in batch mode.

'-cd=DIRECTORY'
     Run GDB using DIRECTORY as its working directory, instead of the
     current directory.

'-fullname'
'-f'
     Emacs sets this option when it runs GDB as a subprocess.  It tells
     GDB to output the full file name and line number in a standard,
     recognizable fashion each time a stack frame is displayed (which
     includes each time the program stops).  This recognizable format
     looks like two '\032' characters, followed by the file name, line
     number and character position separated by colons, and a newline.
     The Emacs-to-GDB interface program uses the two '\032' characters
     as a signal to display the source code for the frame.

'-b BPS'
     Set the line speed (baud rate or bits per second) of any serial
     interface used by GDB for remote debugging.

'-tty=DEVICE'
     Run using DEVICE for your program's standard input and output.


File: gdb.info,  Node: gdbserver man,  Next: gcore man,  Prev: gdb man,  Up: Man Pages

gdbserver man
=============

gdbserver COMM PROG [ARGS...]

gdbserver -attach COMM PID

gdbserver -multi COMM

   'gdbserver' is a program that allows you to run GDB on a different
machine than the one which is running the program being debugged.

Usage (server (target) side)
----------------------------

First, you need to have a copy of the program you want to debug put onto
the target system.  The program can be stripped to save space if needed,
as 'gdbserver' doesn't care about symbols.  All symbol handling is taken
care of by the GDB running on the host system.

   To use the server, you log on to the target system, and run the
'gdbserver' program.  You must tell it (a) how to communicate with GDB,
(b) the name of your program, and (c) its arguments.  The general syntax
is:

     target> gdbserver COMM PROGRAM [ARGS ...]

   For example, using a serial port, you might say:

     target> gdbserver /dev/com1 emacs foo.txt

   This tells 'gdbserver' to debug emacs with an argument of foo.txt,
and to communicate with GDB via '/dev/com1'.  'gdbserver' now waits
patiently for the host GDB to communicate with it.

   To use a TCP connection, you could say:

     target> gdbserver host:2345 emacs foo.txt

   This says pretty much the same thing as the last example, except that
we are going to communicate with the 'host' GDB via TCP. The 'host:2345'
argument means that we are expecting to see a TCP connection from 'host'
to local TCP port 2345.  (Currently, the 'host' part is ignored.)  You
can choose any number you want for the port number as long as it does
not conflict with any existing TCP ports on the target system.  This
same port number must be used in the host GDBs 'target remote' command,
which will be described shortly.  Note that if you chose a port number
that conflicts with another service, 'gdbserver' will print an error
message and exit.

   'gdbserver' can also attach to running programs.  This is
accomplished via the '--attach' argument.  The syntax is:

     target> gdbserver --attach COMM PID

   PID is the process ID of a currently running process.  It isn't
necessary to point 'gdbserver' at a binary for the running process.

   To start 'gdbserver' without supplying an initial command to run or
process ID to attach, use the '--multi' command line option.  In such
case you should connect using 'target extended-remote' to start the
program you want to debug.

     target> gdbserver --multi COMM

Usage (host side)
-----------------

You need an unstripped copy of the target program on your host system,
since GDB needs to examine it's symbol tables and such.  Start up GDB as
you normally would, with the target program as the first argument.  (You
may need to use the '--baud' option if the serial line is running at
anything except 9600 baud.)  That is 'gdb TARGET-PROG', or 'gdb --baud
BAUD TARGET-PROG'.  After that, the only new command you need to know
about is 'target remote' (or 'target extended-remote').  Its argument is
either a device name (usually a serial device, like '/dev/ttyb'), or a
'HOST:PORT' descriptor.  For example:

     (gdb) target remote /dev/ttyb

communicates with the server via serial line '/dev/ttyb', and:

     (gdb) target remote the-target:2345

communicates via a TCP connection to port 2345 on host 'the-target',
where you previously started up 'gdbserver' with the same port number.
Note that for TCP connections, you must start up 'gdbserver' prior to
using the 'target remote' command, otherwise you may get an error that
looks something like 'Connection refused'.

   'gdbserver' can also debug multiple inferiors at once, described in
*note Inferiors and Programs::.  In such case use the 'extended-remote'
GDB command variant:

     (gdb) target extended-remote the-target:2345

   The 'gdbserver' option '--multi' may or may not be used in such case.

   There are three different modes for invoking 'gdbserver':

   * Debug a specific program specified by its program name:

          gdbserver COMM PROG [ARGS...]

     The COMM parameter specifies how should the server communicate with
     GDB; it is either a device name (to use a serial line), a TCP port
     number (':1234'), or '-' or 'stdio' to use stdin/stdout of
     'gdbserver'.  Specify the name of the program to debug in PROG.
     Any remaining arguments will be passed to the program verbatim.
     When the program exits, GDB will close the connection, and
     'gdbserver' will exit.

   * Debug a specific program by specifying the process ID of a running
     program:

          gdbserver --attach COMM PID

     The COMM parameter is as described above.  Supply the process ID of
     a running program in PID; GDB will do everything else.  Like with
     the previous mode, when the process PID exits, GDB will close the
     connection, and 'gdbserver' will exit.

   * Multi-process mode - debug more than one program/process:

          gdbserver --multi COMM

     In this mode, GDB can instruct 'gdbserver' which command(s) to run.
     Unlike the other 2 modes, GDB will not close the connection when a
     process being debugged exits, so you can debug several processes in
     the same session.

   In each of the modes you may specify these options:

'--help'
     List all options, with brief explanations.

'--version'
     This option causes 'gdbserver' to print its version number and
     exit.

'--attach'
     'gdbserver' will attach to a running program.  The syntax is:

          target> gdbserver --attach COMM PID

     PID is the process ID of a currently running process.  It isn't
     necessary to point 'gdbserver' at a binary for the running process.

'--multi'
     To start 'gdbserver' without supplying an initial command to run or
     process ID to attach, use this command line option.  Then you can
     connect using 'target extended-remote' and start the program you
     want to debug.  The syntax is:

          target> gdbserver --multi COMM

'--debug'
     Instruct 'gdbserver' to display extra status information about the
     debugging process.  This option is intended for 'gdbserver'
     development and for bug reports to the developers.

'--remote-debug'
     Instruct 'gdbserver' to display remote protocol debug output.  This
     option is intended for 'gdbserver' development and for bug reports
     to the developers.

'--debug-format=option1[,option2,...]'
     Instruct 'gdbserver' to include extra information in each line of
     debugging output.  *Note Other Command-Line Arguments for
     gdbserver::.

'--wrapper'
     Specify a wrapper to launch programs for debugging.  The option
     should be followed by the name of the wrapper, then any
     command-line arguments to pass to the wrapper, then '--' indicating
     the end of the wrapper arguments.

'--once'
     By default, 'gdbserver' keeps the listening TCP port open, so that
     additional connections are possible.  However, if you start
     'gdbserver' with the '--once' option, it will stop listening for
     any further connection attempts after connecting to the first GDB
     session.


File: gdb.info,  Node: gcore man,  Next: gdbinit man,  Prev: gdbserver man,  Up: Man Pages

gcore
=====

gcore [-o FILENAME] PID

   Generate a core dump of a running program with process ID PID.
Produced file is equivalent to a kernel produced core file as if the
process crashed (and if 'ulimit -c' were used to set up an appropriate
core dump limit).  Unlike after a crash, after 'gcore' the program
remains running without any change.

'-o FILENAME'
     The optional argument FILENAME specifies the file name where to put
     the core dump.  If not specified, the file name defaults to
     'core.PID', where PID is the running program process ID.


File: gdb.info,  Node: gdbinit man,  Prev: gcore man,  Up: Man Pages

gdbinit
=======


~/.gdbinit

./.gdbinit

   These files contain GDB commands to automatically execute during GDB
startup.  The lines of contents are canned sequences of commands,
described in *note Sequences::.

   Please read more in *note Startup::.

'(not enabled with --with-system-gdbinit during compilation)'
     System-wide initialization file.  It is executed unless user
     specified GDB option '-nx' or '-n'.  See more in *note System-wide
     configuration::.

'~/.gdbinit'
     User initialization file.  It is executed unless user specified GDB
     options '-nx', '-n' or '-nh'.

'./.gdbinit'
     Initialization file for current directory.  It may need to be
     enabled with GDB security command 'set auto-load local-gdbinit'.
     See more in *note Init File in the Current Directory::.


File: gdb.info,  Node: Copying,  Next: GNU Free Documentation License,  Prev: Man Pages,  Up: Top

Appendix L GNU GENERAL PUBLIC LICENSE
*************************************

                        Version 3, 29 June 2007

     Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

The GNU General Public License is a free, copyleft license for software
and other kinds of works.

   The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program--to make sure it remains free
software for all its users.  We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to
any other work released this way by its authors.  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

   To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
freedoms that you received.  You must make sure that they, too, receive
or can get the source code.  And you must show them these terms so they
know their rights.

   Developers that use the GNU GPL protect your rights with two steps:
(1) assert copyright on the software, and (2) offer you this License
giving you legal permission to copy, distribute and/or modify it.

   For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

   Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the manufacturer
can do so.  This is fundamentally incompatible with the aim of
protecting users' freedom to change the software.  The systematic
pattern of such abuse occurs in the area of products for individuals to
use, which is precisely where it is most unacceptable.  Therefore, we
have designed this version of the GPL to prohibit the practice for those
products.  If such problems arise substantially in other domains, we
stand ready to extend this provision to those domains in future versions
of the GPL, as needed to protect the freedom of users.

   Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

   The precise terms and conditions for copying, distribution and
modification follow.

TERMS AND CONDITIONS
====================

  0. Definitions.

     "This License" refers to version 3 of the GNU General Public
     License.

     "Copyright" also means copyright-like laws that apply to other
     kinds of works, such as semiconductor masks.

     "The Program" refers to any copyrightable work licensed under this
     License.  Each licensee is addressed as "you".  "Licensees" and
     "recipients" may be individuals or organizations.

     To "modify" a work means to copy from or adapt all or part of the
     work in a fashion requiring copyright permission, other than the
     making of an exact copy.  The resulting work is called a "modified
     version" of the earlier work or a work "based on" the earlier work.

     A "covered work" means either the unmodified Program or a work
     based on the Program.

     To "propagate" a work means to do anything with it that, without
     permission, would make you directly or secondarily liable for
     infringement under applicable copyright law, except executing it on
     a computer or modifying a private copy.  Propagation includes
     copying, distribution (with or without modification), making
     available to the public, and in some countries other activities as
     well.

     To "convey" a work means any kind of propagation that enables other
     parties to make or receive copies.  Mere interaction with a user
     through a computer network, with no transfer of a copy, is not
     conveying.

     An interactive user interface displays "Appropriate Legal Notices"
     to the extent that it includes a convenient and prominently visible
     feature that (1) displays an appropriate copyright notice, and (2)
     tells the user that there is no warranty for the work (except to
     the extent that warranties are provided), that licensees may convey
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          or authors of the material; or

       e. Declining to grant rights under trademark law for use of some
          trade names, trademarks, or service marks; or

       f. Requiring indemnification of licensors and authors of that
          material by anyone who conveys the material (or modified
          versions of it) with contractual assumptions of liability to
          the recipient, for any liability that these contractual
          assumptions directly impose on those licensors and authors.

     All other non-permissive additional terms are considered "further
     restrictions" within the meaning of section 10.  If the Program as
     you received it, or any part of it, contains a notice stating that
     it is governed by this License along with a term that is a further
     restriction, you may remove that term.  If a license document
     contains a further restriction but permits relicensing or conveying
     under this License, you may add to a covered work material governed
     by the terms of that license document, provided that the further
     restriction does not survive such relicensing or conveying.

     If you add terms to a covered work in accord with this section, you
     must place, in the relevant source files, a statement of the
     additional terms that apply to those files, or a notice indicating
     where to find the applicable terms.

     Additional terms, permissive or non-permissive, may be stated in
     the form of a separately written license, or stated as exceptions;
     the above requirements apply either way.

  8. Termination.

     You may not propagate or modify a covered work except as expressly
     provided under this License.  Any attempt otherwise to propagate or
     modify it is void, and will automatically terminate your rights
     under this License (including any patent licenses granted under the
     third paragraph of section 11).

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, you do not qualify to receive new licenses
     for the same material under section 10.

  9. Acceptance Not Required for Having Copies.

     You are not required to accept this License in order to receive or
     run a copy of the Program.  Ancillary propagation of a covered work
     occurring solely as a consequence of using peer-to-peer
     transmission to receive a copy likewise does not require
     acceptance.  However, nothing other than this License grants you
     permission to propagate or modify any covered work.  These actions
     infringe copyright if you do not accept this License.  Therefore,
     by modifying or propagating a covered work, you indicate your
     acceptance of this License to do so.

  10. Automatic Licensing of Downstream Recipients.

     Each time you convey a covered work, the recipient automatically
     receives a license from the original licensors, to run, modify and
     propagate that work, subject to this License.  You are not
     responsible for enforcing compliance by third parties with this
     License.

     An "entity transaction" is a transaction transferring control of an
     organization, or substantially all assets of one, or subdividing an
     organization, or merging organizations.  If propagation of a
     covered work results from an entity transaction, each party to that
     transaction who receives a copy of the work also receives whatever
     licenses to the work the party's predecessor in interest had or
     could give under the previous paragraph, plus a right to possession
     of the Corresponding Source of the work from the predecessor in
     interest, if the predecessor has it or can get it with reasonable
     efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for exercise
     of rights granted under this License, and you may not initiate
     litigation (including a cross-claim or counterclaim in a lawsuit)
     alleging that any patent claim is infringed by making, using,
     selling, offering for sale, or importing the Program or any portion
     of it.

  11. Patents.

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its contributor
     version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To "grant"
     such a patent license to a party means to make such an agreement or
     commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under which
     you make payment to the third party based on the extent of your
     activity of conveying the work, and under which the third party
     grants, to any of the parties who would receive the covered work
     from you, a discriminatory patent license (a) in connection with
     copies of the covered work conveyed by you (or copies made from
     those copies), or (b) primarily for and in connection with specific
     products or compilations that contain the covered work, unless you
     entered into that arrangement, or that patent license was granted,
     prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

     If conditions are imposed on you (whether by court order, agreement
     or otherwise) that contradict the conditions of this License, they
     do not excuse you from the conditions of this License.  If you
     cannot convey a covered work so as to satisfy simultaneously your
     obligations under this License and any other pertinent obligations,
     then as a consequence you may not convey it at all.  For example,
     if you agree to terms that obligate you to collect a royalty for
     further conveying from those to whom you convey the Program, the
     only way you could satisfy both those terms and this License would
     be to refrain entirely from conveying the Program.

  13. Use with the GNU Affero General Public License.

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.

  14. Revised Versions of this License.

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the Free
     Software Foundation.  If the Program does not specify a version
     number of the GNU General Public License, you may choose any
     version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.

  15. Disclaimer of Warranty.

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
     DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.

END OF TERMS AND CONDITIONS
===========================

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR NAME OF AUTHOR

     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

   Also add information on how to contact you by electronic and paper
mail.

   If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

     PROGRAM Copyright (C) YEAR NAME OF AUTHOR
     This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type 'show c' for details.

   The hypothetical commands 'show w' and 'show c' should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

   You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see <http://www.gnu.org/licenses/>.

   The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read <http://www.gnu.org/philosophy/why-not-lgpl.html>.


File: gdb.info,  Node: GNU Free Documentation License,  Next: Concept Index,  Prev: Copying,  Up: Top

Appendix M GNU Free Documentation License
*****************************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     <http://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.  We
     recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it can
     be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You accept
     the license if you copy, modify or distribute the work in a way
     requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in the
     notice that says that the Document is released under this License.
     If a section does not fit the above definition of Secondary then it
     is not allowed to be designated as Invariant.  The Document may
     contain zero Invariant Sections.  If the Document does not identify
     any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images composed
     of pixels) generic paint programs or (for drawings) some widely
     available drawing editor, and that is suitable for input to text
     formatters or for automatic translation to a variety of formats
     suitable for input to text formatters.  A copy made in an otherwise
     Transparent file format whose markup, or absence of markup, has
     been arranged to thwart or discourage subsequent modification by
     readers is not Transparent.  An image format is not Transparent if
     used for any substantial amount of text.  A copy that is not
     "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and standard-conforming
     simple HTML, PostScript or PDF designed for human modification.
     Examples of transparent image formats include PNG, XCF and JPG.
     Opaque formats include proprietary formats that can be read and
     edited only by proprietary word processors, SGML or XML for which
     the DTD and/or processing tools are not generally available, and
     the machine-generated HTML, PostScript or PDF produced by some word
     processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     The "publisher" means any person or entity that distributes copies
     of the Document to the public.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow the
     conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the title
     equally prominent and visible.  You may add other material on the
     covers in addition.  Copying with changes limited to the covers, as
     long as they preserve the title of the Document and satisfy these
     conditions, can be treated as verbatim copying in other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a machine-readable
     Transparent copy along with each Opaque copy, or state in or with
     each Opaque copy a computer-network location from which the general
     network-using public has access to download using public-standard
     network protocols a complete Transparent copy of the Document, free
     of added material.  If you use the latter option, you must take
     reasonably prudent steps, when you begin distribution of Opaque
     copies in quantity, to ensure that this Transparent copy will
     remain thus accessible at the stated location until at least one
     year after the last time you distribute an Opaque copy (directly or
     through your agents or retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of copies,
     to give them a chance to provide you with an updated version of the
     Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with the
     Modified Version filling the role of the Document, thus licensing
     distribution and modification of the Modified Version to whoever
     possesses a copy of it.  In addition, you must do these things in
     the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of previous
          versions (which should, if there were any, be listed in the
          History section of the Document).  You may use the same title
          as a previous version if the original publisher of that
          version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on the
          Title Page.  If there is no section Entitled "History" in the
          Document, create one stating the title, year, authors, and
          publisher of the Document as given on its Title Page, then add
          an item describing the Modified Version as stated in the
          previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in the
          "History" section.  You may omit a network location for a work
          that was published at least four years before the Document
          itself, or if the original publisher of the version it refers
          to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the section
          all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document, unaltered
          in their text and in their titles.  Section numbers or the
          equivalent are not considered part of the section titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option designate
     some or all of these sections as invariant.  To do this, add their
     titles to the list of Invariant Sections in the Modified Version's
     license notice.  These titles must be distinct from any other
     section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end of
     the list of Cover Texts in the Modified Version.  Only one passage
     of Front-Cover Text and one of Back-Cover Text may be added by (or
     through arrangements made by) any one entity.  If the Document
     already includes a cover text for the same cover, previously added
     by you or by arrangement made by the same entity you are acting on
     behalf of, you may not add another; but you may replace the old
     one, on explicit permission from the previous publisher that added
     the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination all
     of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the documents
     in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow this
     License in all other respects regarding verbatim copying of that
     document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of a
     storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense, or distribute it is void,
     and will automatically terminate your rights under this License.

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, receipt of a copy of some or all of the
     same material does not give you any rights to use it.

  10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     <http://www.gnu.org/copyleft/>.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If the
     Document does not specify a version number of this License, you may
     choose any version ever published (not as a draft) by the Free
     Software Foundation.  If the Document specifies that a proxy can
     decide which future versions of this License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

  11. RELICENSING

     "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
     World Wide Web server that publishes copyrightable works and also
     provides prominent facilities for anybody to edit those works.  A
     public wiki that anybody can edit is an example of such a server.
     A "Massive Multiauthor Collaboration" (or "MMC") contained in the
     site means any set of copyrightable works thus published on the MMC
     site.

     "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
     published by that same organization.

     "Incorporate" means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is "eligible for relicensing" if it is licensed under this
     License, and if all works that were first published under this
     License somewhere other than this MMC, and subsequently
     incorporated in whole or in part into the MMC, (1) had no cover
     texts or invariant sections, and (2) were thus incorporated prior
     to November 1, 2008.

     The operator of an MMC Site may republish an MMC contained in the
     site under CC-BY-SA on the same site at any time before August 1,
     2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts."  line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.

