Bug#165992: gcc: __builtin_return_address doesn't work properly

[Daniel Jacobowitz <dan@debian.org>]

On Wed, Oct 23, 2002 at 02:01:47AM -0400, gsstark@mit.edu wrote:
> Package: gcc
> Version: 2:2.95.4-17
> Severity: normal
> 
> The following program illustrates that __builtin_return_address seg faults when
> you reach the top of the stack rather than returning 0 as it is specified in
> the gcc manual. 
> 
> I see the same behaviour with both gcc 2.95 and gcc 3.0.

GCC 3.2 says:
     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.

You're running it beyond the top of the stack.  It returns a random
value, and then the following call crashes.  The documentation is
correct and it really can't do any better.

> 
> 
> #include <stdio.h>
> 
> int main () {a();}
> a() {b();}
> b() {c();}
> c()
> {
>   printf("%d: %p\n", 0, __builtin_return_address(0));
>   printf("%d: %p\n", 1, __builtin_return_address(1));
>   printf("%d: %p\n", 2, __builtin_return_address(2));
>   printf("%d: %p\n", 3, __builtin_return_address(3));
>   printf("%d: %p\n", 4, __builtin_return_address(4));
>   printf("%d: %p\n", 5, __builtin_return_address(5));
> }
> 
> 
> (gdb) run
> Starting program: /tmp/a.out 
> 0: 0x804840f
> 1: 0x80483ff
> 2: 0x80483ef
> 3: 0x400450bf
> 4: 0x8048331
> (no debugging symbols found)...(no debugging symbols found)...
> Program received signal SIGSEGV, Segmentation fault.
> 0x080484ae in c ()
> (gdb) bt
> #0  0x080484ae in c ()
> #1  0x0804840f in b ()
> #2  0x080483ff in a ()
> #3  0x080483ef in main ()
> #4  0x400450bf in __libc_start_main () from /lib/libc.so.6
> 
> 
> -- System Information
> Debian Release: testing/unstable
> Kernel Version: Linux stark.dyndns.tv 2.4.19 #6 Tue Sep 10 22:08:51 EDT 2002 i686 unknown unknown GNU/Linux
> 
> Versions of the packages gcc depends on:
> ii  cpp            2.95.4-17      The GNU C preprocessor.
> ii  cpp-2.95       2.95.4-12      The GNU C preprocessor.
> ii  gcc-2.95       2.95.4-12      The GNU C compiler.
> 
> 
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> 

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer