Re: RFA: try to ensure abort has valid return address

[Andrew Cagney <ac131313@cygnus.com>]

> 2002-01-12  Jim Blandy  <jimb@redhat.com>
> 
> * gdb.base/coremaker.c (func2): Try to arrange for the return
> 	address passed to `abort' to fall within `func2', so we can get
> 	backtraces.
> 
> Index: gdb/testsuite/gdb.base/coremaker.c
> ===================================================================
> RCS file: /cvs/cvsfiles/devo/gdb/testsuite/gdb.base/coremaker.c,v
> retrieving revision 1.4
> diff -c -r1.4 coremaker.c
> *** gdb/testsuite/gdb.base/coremaker.c	1999/06/25 23:44:28	1.4
> --- gdb/testsuite/gdb.base/coremaker.c	2002/01/12 06:42:09
> ***************
> *** 81,87 ****
>   }
>   
>   void
> ! func2 ()
>   {
>     int coremaker_local[5];
>     int i;
> --- 81,87 ----
>   }
>   
>   void
> ! func2 (int please_abort)
>   {
>     int coremaker_local[5];
>     int i;
> ***************
> *** 104,116 ****
>     for (i = 0; i < 5; i++)
>       coremaker_bss += coremaker_local[i];
>     coremaker_data = coremaker_ro + 1;
> !   abort ();
>   }
>   
>   void
>   func1 ()
>   {
> !   func2 ();
>   }
>   
>   int main ()
> --- 104,138 ----
>     for (i = 0; i < 5; i++)
>       coremaker_bss += coremaker_local[i];
>     coremaker_data = coremaker_ro + 1;
> ! 
> !   /* This function used to simply call `abort' unconditionally.
> !      However, because GCC sometimes knows that `abort' will never
> !      return, the `call' instruction that invokes `abort' would
> !      sometimes be the very last instruction in this function.  The
> !      epilogue instructions you'd normally expect --- deallocating the
> !      frame, jumping to the return address --- were omitted, since
> !      they'd never be reached anyway.  This means that the return
> !      address passed to abort (which it'll never use) actually points
> !      beyond the end of the caller!  Sometimes the return address
> !      seemed to be in the next function; sometimes it seemed to be in
> !      padding instructions between functions, for which there was no
> !      line number info.  In any case, GDB had difficulties producing a
> !      backtrace in this case.
> ! 
> !      There's no way to force the compiler not to put the call to
> !      `abort' at the very end of the function --- after all, it is
> !      functionally correct to do so.  But we hope that putting it in a
> !      conditional will make it more likely that GDB can get a
> !      backtrace, and find coremaker_local, which is what we really care
> !      about.  */
> !   if (please_abort)
> !     abort ();
>   }
>   
>   void
>   func1 ()
>   {
> !   func2 (1);
>   }
>   
>   int main ()
> 
>