This is the unwind specification draft for GNU/Linux/ia64 which extends the exception ABI:
http://www.codesourcery.com/cxx-abi/abi-eh.html
The goal is to allow any ABI conforming shared unwind library to be used with output from any ABI compliant GNU/Linux compiler.
The GNU/Linux/ia64 extension of the "Level I. Base ABI" section in the exception ABI:
1. An implementation of a shared unwind library shall place the unwind library in a DSO named libunwind.so.7 or in auxiliary DSOs automatically loaded by it.
2. A new unwind action:
const _Unwind_Action _UA_END_OF_STACK = 16;
In order to allow _Unwind_ForcedUnwind to perform special processing when it reaches the end of the stack, the unwind runtime will call the stop function after the last frame is rejected, with the _UA_END_OF_STACK bit set. The stop function may catch this condition by noticing that the _UA_END_OF_STACK bit is set. The stop function may return _URC_END_OF_STACK if it cannot handle the end of stack condition.
3. Additional functions:
a. Use unwind data to perform a stack backtrace. The trace callback is called for every stack frame in the call chain, but no cleanup actions are performed.
typedef _Unwind_Reason_Code (*_Unwind_Trace_Fn)
(struct _Unwind_Context *, void *);
extern _Unwind_Reason_Code _Unwind_Backtrace (_Unwind_Trace_Fn, void *);
b. Retrieve the CFA of the given context.
extern _Unwind_Word _Unwind_GetCFA (struct _Unwind_Context *);
c. Resume propagation of an FORCE_UNWIND exception, or to rethrow a normal exception that was handled. */
extern _Unwind_Reason_Code _Unwind_Resume_or_Rethrow (struct _Unwind_Exception *);
d. Given an address, return the entry point of the function that contains it.
extern void * _Unwind_FindEnclosingFunction (void *pc);
e. Retrieve the Backing Store Pointer of the given context. Only for ia64.
extern _Unwind_Word _Unwind_GetBSP (struct _Unwind_Context *);
f. Retrieve the base addresses for data-relative addressing in the LDSA. Only for non-ia64 platforms.
extern _Unwind_Ptr _Unwind_GetDataRelBase (struct _Unwind_Context *);
g. Retrieve the base addresses for text-relative addressing in the LDSA. Only for non-ia64 platforms.
extern _Unwind_Ptr _Unwind_GetTextRelBase (struct _Unwind_Context *);
h. Retrieve the object containing the address. Only for non-ia64 platforms.
extern const fde * _Unwind_Find_FDE (void *, struct dwarf_eh_bases *);
Other GNU/Linux platforms shall adopt the above specification if the platform ABI doesn't specify an alternate unwind mechanism.
Backward compatibility for the existing libgcc-based unwinder:
If there is an existing libgcc-based unwinder in gcc and an unwind library supports gcc, a set of compatibility symbols should be defined.
1. __libunwind_Unwind_Backtrace: Alias of _Unwind_Backtrace
2. __libunwind_Unwind_DeleteException: Alias of _Unwind_DeleteException
3. __libunwind_Unwind_FindEnclosingFunction: Alias of _Unwind_FindEnclosingFunction
4. __libunwind_Unwind_ForcedUnwind: Alias of _Unwind_ForcedUnwind
5. __libunwind_Unwind_GetCFA: Alias of _Unwind_GetCFA
6. __libunwind_Unwind_GetGR: Alias of _Unwind_GetGR
7. __libunwind_Unwind_GetIP: Alias of _Unwind_GetIP
8. __libunwind_Unwind_GetLanguageSpecificData: Alias of _Unwind_GetLanguageSpecificData
9. __libunwind_Unwind_GetRegionStart: Alias of _Unwind_GetRegionStart
10.__libunwind_Unwind_RaiseException: Alias of _Unwind_RaiseException
11.__libunwind_Unwind_Resume: Alias of _Unwind_Resume
12.__libunwind_Unwind_Resume_or_Rethrow: Alias of _Unwind_Resume_or_Rethrow
13.__libunwind_Unwind_SetGR: Alias of _Unwind_SetGR
14.__libunwind_Unwind_SetIP: Alias of _Unwind_SetIP
15.__libunwind_Unwind_GetBSP: Alias of _Unwind_GetBSP. Only for ia64.
16.__libunwind_Unwind_GetDataRelBase: Alias of _Unwind_GetDataRelBase. Only for non-ia64 platforms.
17.__libunwind_Unwind_GetTextRelBase: Alias of _Unwind_GetTextRelBase. Only for non-ia64 platforms.
18.__libunwind_Unwind_Find_FDE: Alias of _Unwind_Find_FDE. Only for non-ia64 platforms.
Those symbols can be used by the new libgcc to provide the backward binary compatibility.