ld(1)

NAME
ld - the GNU linker

SYNOPSIS

ld  [-o output ] objfiles ...
    [-A architecture ] [-b input-format ] [-Bstatic] [-c commandfile ] [-d|-dc|-dp ]
    [-defsym symbol = expression ] [-e entry ] [-F] [-F format ] [-format input-format ] [-g] [-i] [-l ar ] [-L searchdir ] [-M|-m] [-n|-N] [-noinhibit-exec] [-R filename ] [-relax] [-r|-Ur] [-S] [-s] [-T commandfile ] [-Ttext textorg ] [-Tdata dataorg ] [-Tbss bssorg ] [-t] [-u sym ] [-v] [-X] [-x] [{ script }]

DESCRIPTION
ld combines a number of object and archive files, relocates their data and ties up symbol references. Often the last step in building a new compiled program to run is a call to ld . ld accepts Linker Command Language files to provide explicit and total control over the linking process. This man page does not describe the command language; see the `ld ' entry in `info ', or the manual ld: the GNU linker , for full details on the command language and on other aspects of the GNU linker. This version of ld uses the general purpose BFD libraries to operate on object files. This allows ld to read, combine, and write object files in many different formats—for example, COFF or a.out . Different formats may be linked together to produce any available kind of object file. You can use `objdump -i ' to get a list of formats supported on various architectures; see objdump(1). Aside from its flexibility, the GNU linker is more helpful than other linkers in providing diagnostic information. Many linkers abandon execution immediately upon encountering an error; whenever possible, ld continues executing, allowing you to identify other errors (or, in some cases, to get an output file in spite of the error). The GNU linker ld is meant to cover a broad range of situations, and to be as compatible as possible with other linkers. As a result, you have many choices to control its behavior through the command line, and through environment variables.

OPTIONS
The plethora of command-line options may seem intimidating, but in actual practice few of them are used in any particular context. For instance, a frequent use of ld is to link standard Unix object files on a standard, supported Unix system. On such a system, to link a file hello.o :

$ ld -o output /lib/crt0.o hello.o -lc

This tells ld to produce a file called output as the result of linking the file /lib/crt0.o with hello.o and the library libc.a which will come from the standard search directories. The command-line options to ld may be specified in any order, and may be repeated at will. For the most part, repeating an option with a different argument will either have no further effect, or override prior occurrences (those further to the left on the command line) of an option. The exceptions—which may meaningfully be used more than once—are -A , -b (or its synonym -format ), -defsym , -L , -l , -R , and -u . The list of object files to be linked together, shown as objfiles , may follow, precede, or be mixed in with command-line options; save that an objfiles argument may not be placed between an option flag and its argument. Usually the linker is invoked with at least one object file, but other forms of binary input files can also be specified with -l , -R , and the script command language. If no binary input files at all are specified, the linker does not produce any output, and issues the message `No input files '. Option arguments must either follow the option letter without intervening whitespace, or be given as separate arguments immediately following the option that requires them.

objfiles...
    The object files objfiles to be linked.

-Aarchitecture
    In the current release of ld , this option is useful only for the Intel 960 family of architectures. In that ld configuration, the architecture argument is one of the two-letter names identifying members of the 960 family; the option specifies the desired output target, and warns of any incompatible instructions in the input files. It also modifies the linker's search strategy for archive libraries, to support the use of libraries specific to each particular architecture, by including in the search loop names suffixed with the string identifying the architecture. For example, if your ld command line included `-ACA ' as well as `-ltry ', the linker would look (in its built-in search paths, and in any paths you specify with -L ) for a library with the names

    try
    libtry.a
    tryca
    libtryca.a

    The first two possibilities would be considered in any event; the last two are due to the use of `-ACA '. Future releases of ld may support similar functionality for other architecture families. You can meaningfully use -A more than once on a command line, if an architecture family allows combination of target architectures; each use will add another pair of name variants to search for when -l specifies a library.

-b input-format
    Specify the binary format for input object files that follow this option on the command line. You don't usually need to specify this, as ld is configured to expect as a default input format the most usual format on each machine. input-format is a text string, the name of a particular format supported by the BFD libraries. -format input-format has the same effect. You may want to use this option if you are linking files with an unusual binary format. You can also use -b to switch formats explicitly (when linking object files of different formats), by including -b input-format before each group of object files in a particular format. The default format is taken from the environment variable GNUTARGET . You can also define the input format from a script, using the command TARGET .

-Bstatic
    This flag is accepted for command-line compatibility with the SunOS linker, but has no effect on ld .

-c commandfile
    Directs ld to read link commands from the file commandfile . These commands will completely override ld 's default link format (rather than adding to it); commandfile must specify everything necessary to describe the target format. You may also include a script of link commands directly in the command line by bracketing it between `{ ' and `} ' characters.

-d

-dc

-dp These three options are equivalent; multiple forms are supported for compatibility with other linkers. Use any of them to make ld assign space to common symbols even if a relocatable output file is specified (-r ). The script command FORCE_COMMON_ALLOCATION has the same effect.

-defsym symbol
    = expression Create a global symbol in the output file, containing the absolute address given by expression . You may use this option as many times as necessary to define multiple symbols in the command line. A limited form of arithmetic is supported for the expression in this context: you may give a hexadecimal constant or the name of an existing symbol, or use + and - to add or subtract hexadecimal constants or symbols. If you need more elaborate expressions, consider using the linker command language from a script.

-e entry
    Use entry as the explicit symbol for beginning execution of your program, rather than the default entry point. for a discussion of defaults and other ways of specifying the entry point.

-F

-Fformat
    Some older linkers used this option throughout a compilation toolchain for specifying object-file format for both input and output object files. ld 's mechanisms (the -b or -format options for input files, the TARGET command in linker scripts for output files, the GNUTARGET environment variable) are more flexible, but but it accepts (and ignores) the -F option flag for compatibility with scripts written to call the old linker.

-format input-format
    Synonym for -b input-format .

-g  Accepted, but ignored; provided for compatibility with other tools.

-i  Perform an incremental link (same as option -r ).

-lar
    Add an archive file ar to the list of files to link. This option may be used any number of times. ld will search its path-list for occurrences of lib ar .afor every ar specified.

-Lsearchdir
    This command adds path searchdir to the list of paths that ld will search for archive libraries. You may use this option any number of times. The default set of paths searched (without being specified with -L ) depends on what emulation mode ld is using, and in some cases also on how it was configured. The paths can also be specified in a link script with the SEARCH_DIR command.

-M

-m  Print (to the standard output file) a link map—diagnostic information about where symbols are mapped by ld , and information on global common storage allocation.

-N  specifies readable and writable text and data sections. If the output format supports Unix style magic numbers, the output is marked as OMAGIC . When you use the `-N ' option, the linker does not page-align the data segment.

-n  sets the text segment to be read only, and NMAGIC is written if possible.

-noinhibit-exec
    Normally, the linker will not produce an output file if it encounters errors during the link process. With this flag, you can specify that you wish the output file retained even after non-fatal errors.

-o output
    output output is a name for the program produced by ld ; if this option is not specified, the name `a.out ' is used by default. The script command OUTPUT can also specify the output file name.

-R filename
    file Read symbol names and their addresses from filename , but do not relocate it or include it in the output. This allows your output file to refer symbolically to absolute locations of memory defined in other programs.

-relax
    An option with machine dependent effects. Currently this option is only supported on the H8/300. On some platforms, use this option to perform global optimizations that become possible when the linker resolves addressing in your program, such as relaxing address modes and synthesizing new instructions in the output object file. On platforms where this is not supported, `-relax ' is accepted, but has no effect.

-r  Generates relocatable output—i.e., generate an output file that can in turn serve as input to ld . This is often called partial linking. As a side effect, in environments that support standard Unix magic numbers, this option also sets the output file's magic number to OMAGIC . If this option is not specified, an absolute file is produced. When linking C++ programs, this option will not resolve references to constructors; -Ur is an alternative. This option does the same as -i .

-S  Omits debugger symbol information (but not all symbols) from the output file.

-s  Omits all symbol information from the output file.

{ script }
    You can, if you wish, include a script of linker commands directly in the command line instead of referring to it via an input file. When the character `{ ' occurs on the command line, the linker switches to interpreting the command language until the end of the list of commands is reached—flagged with a closing brace `} '. Other command-line options will not be recognized while parsing the script. See the `ld ' entry in `info ', or the manual ld: the GNU linker , for a description of the command language.

-Tbss org

-Tdata org

-Ttext org
    Use org as the starting address for—respectively—the bss , data , or the text segment of the output file. textorg must be a hexadecimal integer.

-T commandfile

-Tcommandfile
    Equivalent to -c commandfile ; supported for compatibility with other tools.

-t  Prints names of input files as ld processes them.

-u sym
    Forces sym to be entered in the output file as an undefined symbol. This may, for example, trigger linking of additional modules from standard libraries. -u may be repeated with different option arguments to enter additional undefined symbols.

-Ur For anything other than C++ programs, this option is equivalent to -r : it generates relocatable output—i.e., an output file that can in turn serve as input to ld . When linking C++ programs, -Ur will resolve references to constructors, unlike -r .

-v  Display the version number for ld .

-X  If -s or -S is also specified, delete only local symbols beginning with `L '.

-x  If -s or -S is also specified, delete all local symbols, not just those beginning with `L '.

ENVIRONMENT
ld always consults two environment variables: GNUTARGET and LDEMULATION . Depending on the setting of the latter, other environment variables may be used as well. GNUTARGET determines the input-file object format if you don't use -b (or its synonym -format ). Its value should be one of the BFD names for an input format. If there is no GNUTARGET in the environment, ld uses the natural format of the host. If GNUTARGET is set to default then BFD attempts to discover the input format by examining binary input files; this method often succeeds, but there are potential ambiguities, since there is no method of ensuring that the magic number used to flag object-file formats is unique. However, the configuration procedure for BFD on each system places the conventional format for that system first in the search-list, so ambiguities are resolved in favor of convention. LDEMULATION controls some aspects of ld 's dominant personality. Although ld is flexible enough to permit its use in many contexts regardless of configuration, you can use this variable to make it act more like one or another older linker by default. In particular, the value of LDEMULATION controls what default linker script is used (thereby controlling the default input and output formats; ; what default paths are searched for archive libraries; and in some cases whether additional linker script commands are available. Here is the current set of emulations available:

LDEMULATION=gld
    Emulate the older GNU linker. When this emulation is selected, the default library search paths are

    /lib
    /usr/lib
    /usr/local/lib/lib

    The default output format is set to a.out-generic-big , and the default machine is the system's configured BFD default.

LDEMULATION=gld68k
    A variant of the gld emulation; only differs in specifically setting the default BFD machine as m68k .

LDEMULATION=gld960
    Emulate the Intel port of the older gld for the i960 architectures. The default library search paths are taken from two other environment variables, G960LIB and G960BASE . The default architecture is i960 . The default output format is set to b.out.big , and in fact the default output file name (if -o is not specified) is b.out , to reflect this variant format, for this emulation. This emulation can behave slightly differently depending on the setting of the ld compile-time switch GNU960 . If ld is compiled with GNU960 defined, then an additional environment variable—GNUTARGET —is available; its value, if available, specifies some other default output format than b.out.big .

LDEMULATION=gldm88kbcs
    Sets the output format to m88kbcs and the architecture to m88k . Default library search paths are

    /lib
    /usr/lib
    /usr/local/lib

LDEMULATION=lnk960
    Emulate the Intel linker lnk960 . The default output format is coff-Intel-big . With this emulation, ld supports the additional script commands HLL and SYSLIB for specification of library archives. This is the only emulation with extensive support for the -A (architecture) command-line option. By default, the architecture CORE is assumed, but you can choose additional features from the i960 architecture family by using one of the following with -A (or by using the OUTPUT_ARCH command from a script):

    CORE
    KB
    SB
    MC
    XA
    CA
    KA
    SA

    The default libraries are chosen with some attention to the architecture selected; the core library `cg ' is always included, but the library fpg is also used if you've specified any of the architectures KA , SA , or CA . Like gld960 , this emulation uses additional environment variables to set the default library search paths. Also like gld960 , the behavior of this emulation is slightly different depending on whether ld itself was compiled with GNU960 defined. If your ld was compiled with GNU960 defined, the default paths are taken from all three of G960LIB , G960BASE , and I960BASE . For the first two, paths you supply are automatically suffixed with `/lib/libcoff '; for the last, your path is automatically suffixed with `/lib '. If your ld was not compiled with GNU960 defined, the default paths are taken from I960BASE , and G960BASE is only consulted if I960BASE is undefined. In this case G960LIB is not used at all.

LDEMULATION=vanilla
    This is the least specific setting for ld . You can set LDEMULATION=vanilla to disable emulation of other linkers. This setting makes ld take the default machine from the BFD configuration on your system; a.out-generic-big is the default target. No other defaults are specified.

SEE ALSO
objdump(1)
`ld' and `binutils' entries in info
ld: the GNU linker, Steve Chamberlain and Roland Pesch; The GNU Binary Utilities, Roland H. Pesch.

COPYING
Copyright (c) 1991, 1992 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English.