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PR71951: Fix unwinding with -fomit-frame-pointer 

As described in PR71951, if libgcc is built with -fomit-frame-pointer,
unwinding crashes, for example while doing a backtrace.  The underlying
reason is the Dwarf unwinder does not setup the frame pointer register
in the initialization code.  When later unwinding a function that uses
the frame pointer, it tries to read FP using _Unwind_GetGR, and this
crashes if has never restored FP.  To unwind correctly the first frame
must save and restore FP (it is unwound in a special way so that it
uses SP instead of FP).  This is done by adding -fno-omit-frame-pointer.

    gcc/
	PR target/71951
	* config/aarch64/aarch64.h (LIBGCC2_UNWIND_ATTRIBUTE): Define.

From-SVN: r253063
This commit is contained in:
Wilco Dijkstra 2017-09-21 12:16:31 +00:00 committed by Wilco Dijkstra
parent 6445b688e5
commit c568955a6d
2 changed files with 13 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2017-09-21 Wilco Dijkstra <wdijkstr@arm.com>
PR target/71951
* config/aarch64/aarch64.h (LIBGCC2_UNWIND_ATTRIBUTE): Define.
2017-09-19 Uros Bizjak <ubizjak@gmail.com>
* config/i386/i386.c (fold_builtin_cpu): Add M_AMDFAM17H

8
gcc/config/aarch64/aarch64.h
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@ -958,4 +958,12 @@ extern const char *host_detect_local_cpu (int argc, const char **argv);
extern tree aarch64_fp16_type_node;
extern tree aarch64_fp16_ptr_type_node;
/* The generic unwind code in libgcc does not initialize the frame pointer.
So in order to unwind a function using a frame pointer, the very first
function that is unwound must save the frame pointer. That way the frame
pointer is restored and its value is now valid - otherwise _Unwind_GetGR
crashes. Libgcc can now be safely built with -fomit-frame-pointer. */
#define LIBGCC2_UNWIND_ATTRIBUTE \
__attribute__((optimize ("no-omit-frame-pointer")))
#endif /* GCC_AARCH64_H */