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Re: RFA: try to ensure abort has valid return address
- From: Fernando Nasser <fnasser at redhat dot com>
- To: Jim Blandy <jimb at cygnus dot com>
- Cc: gdb-patches at sources dot redhat dot com
- Date: Mon, 21 Jan 2002 11:28:46 -0500
- Subject: Re: RFA: try to ensure abort has valid return address
- Organization: Red Hat Canada
- References: <20020112064706.52E575E9D8@zwingli.cygnus.com>
I wonder if we will always be able to trick the compiler with
this, but it is worthy of a try.
Approved.
Thanks Jim.
Fernando
Jim Blandy wrote:
>
> 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 ()
--
Fernando Nasser
Red Hat Canada Ltd. E-Mail: fnasser@redhat.com
2323 Yonge Street, Suite #300
Toronto, Ontario M4P 2C9