[Crash-utility] [PATCH] Use backtrace() instead of __builtin_return_address()

[Dave Anderson]

Bernhard Walle wrote:
> When crash is compiled with gcc 4.3 and -O2, the __builtin_return_address()
> causes crash to crash. See also [1] for a discussion about that.

It appears that [1] only describes a problem if you ask for more frames
than exist.  Given the usage in crash, it's impossible to have a frame count
of less than 4.  So it must be some other bug, no?

Dave

> The gcc documentation [2] says
> 
> 	__builtin_return_address()
> 
> 	On some machines it may be impossible to determine the return address of
> 	any function other than the current one; in such cases, or when the top
> 	of the stack has been reached, this function will return 0 or a random
> 	value. In addition, __builtin_frame_address may be used to determine if
> 	the top of the stack has been reached.
> 	
> 	This function should only be used with a nonzero argument for debugging
> 	purposes.
> 
> Even the __builtin_frame_address() does not work here. Instead of checking
> if the crash is built with -O2 and introducing new preprocessor checks here,
> I use the backtrace() function which is available via glibc. This works here
> (tested without the other patch which brought my attention to this bug).
> 
> Since crash only runs on Linux (IIRC), the glibc dependency should not be
> a problem.
> 
> Signed-off-by: Bernhard Walle <bwalle at suse.de>
> 
> 
> [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=165992
> [2] http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html
> 
> ---
>  defs.h |   10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> --- a/defs.h
> +++ b/defs.h
> @@ -1803,15 +1803,7 @@ struct alias_data {                 /* c
>  static inline void
>  save_return_address(ulong *retaddr)
>  {
> -	retaddr[0] = (ulong) __builtin_return_address(0);
> -#if defined(X86) || defined(PPC) || defined(X86_64) || defined(PPC64)
> -	if (__builtin_frame_address(1))
> -		retaddr[1] = (ulong) __builtin_return_address(1);
> -	if (__builtin_frame_address(2))
> -                retaddr[2] = (ulong) __builtin_return_address(2);
> -	if (__builtin_frame_address(3))
> -                retaddr[3] = (ulong) __builtin_return_address(3);
> -#endif
> +	backtrace(retaddr, 4);
>  }
>  
>  #endif /* !GDB_COMMON */
> 
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