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Possible improvement to i386 function prologue analysis.
- From: ashish mittal <ashishm at linsyssoft dot com>
- To: gdb at sources dot redhat dot com
- Date: Fri, 15 Oct 2004 18:18:50 +0530
- Subject: Possible improvement to i386 function prologue analysis.
Hi,
This is in reference to GDB's function prologue analysis (and updation
of its internal register cache therefrom) on the x86 architecture.
GDB file: gdb/i386-tdep.c
i386_analyze_frame_setup() takes care of
"Check for some special instructions that might be migrated by
GCC into the prologue and skip them. At this point in the
prologue, code should only touch the scratch registers %eax,
%ecx and %edx,.."
Instances have been observed when GCC generates these instructions
between the prologue "push" instructions; for example, the following
from the objdump of gdb:
0807a380 <captured_main>:
807a380: 55 push %ebp
807a381: 31 c0 xor %eax,%eax
807a383: 89 e5 mov %esp,%ebp
807a385: 57 push %edi
807a386: 31 d2 xor %edx,%edx
807a388: 31 c9 xor %ecx,%ecx
807a38a: 56 push %esi
807a38b: 53 push %ebx
807a38c: 81 ec 4c 01 00 00 sub $0x14c,%esp
In the above instance, the function "i386_analyze_register_saves()",
which takes care of populating the frame cache, will fail after reading
the first register %edi.
Please suggest if it would be worthwhile to work on a similar check for
special instructions within the for loop in i386_analyze_register_saves().
This will enable it to continue reading saved registers over such
occurances.
I could work on a possible patch if you agree.
Thanks,
Ashish Mittal.