Re: [PATCH] Partial fix for PR backtrace/1718

[Mark Kettenis <kettenis@chello.nl>]

[Sorry Michael and Eli, I managed to remove the Subject: line and
 therefore the list didn't accept this message]

   Date: Sun, 01 Aug 2004 01:35:39 -0400
   From: Michael Chastain <mec.gnu@mindspring.com>

   "Eli Zaretskii" <eliz@gnu.org> wrote:
   > Perhaps, then, you could post a list of all the opcodes and subsequent
   > bytes that we need to cover in i386_analyze_frame_setup?

   The compiler could schedule just about anything into the prologue!

There are some restrictions though, given that GCC can only play with
a limited set of registers.

   Let's get empirical.  I ran cc1plus and gdb through "objdump -d" and
   some perl fu.

Thanks!  This really is the info I need.  Could you post (or mail me)
the perl fu?

   We have to have "mov 0xADDRESS, %reg".  After that, recognizing
   "cmpl $IMMEDIATE, 0xADDRESS" would help.  That instruction gets scheduled
   even before "push %ebp".  Those two additions would cover 99.9% of cc1plus
   and gdb.

On System V ABI conforming systems, yes.  On systems that use the
-freg-struct-return by default (FreeBSD, OpenBSD, Cygwin and a few
others) I guess there are a bit more possibilities.  I'll try to
address -freg-struct-return too.

Anyway, I've got some ideas to make the prologue analyzer easily
extendable.

   [snip]

   The 10 truly freaky prologues are:

     .plt : pushl 0x86039e8 | jmp *0x86039ec | add %al, (%eax) | add %al, (%eax) | jmp *0x86039f0 | push $0x0 | jmp 80494cc <_init+0x18>

That's the PLT.  GDB should already handle that one, and otherwise
it'd deserve (and need) a special frame unwinder anyway like I did for
SPARC.

     _start : xor %ebp, %ebp | pop %esi | mov %esp, %ecx | and $0xfffffff0, %esp | push %eax | push %esp | push %edx

This one is rather special since it's the entry point.

Thanks!

Mark