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Re: STABS records for 64-bit function arguments via registers in i386
- From: Mark Kettenis <mark dot kettenis at xs4all dot nl>
- To: kew at emc dot com
- Cc: gdb at sourceware dot org
- Date: Wed, 13 Oct 2010 18:07:29 +0200 (CEST)
- Subject: Re: STABS records for 64-bit function arguments via registers in i386
- References: <4CB5CB63.email@example.com>
> Date: Wed, 13 Oct 2010 11:08:19 -0400
> From: firstname.lastname@example.org
> In i386 architecture (32 bit) gcc can optimize a static function to pass
> function arguments via registers (instead of in the stack). For 64-bit
> arguments, it uses 2 registers, but gdb reports only 1 (via "info
> scope") when the binary being debugged is compiled using the STABS
> debugging format.
> I checked using objdump and could see indeed only 1 N_RSYM record being
> given (so no wonder gdb would only report 1 register).
> How does the STABS debugging format indicate the 2 registers used for
> passing 64 function arguments in i386 architecture? Is this supported?
Historically the convention has been that a 64-bit value is stored in
register N and N + 1, where N is the register number that's stored in
the STABS debugging information.
If your compiler doesn't store 64-bit values in that way (and I think
modern versions of GCC no longer do this) things will break.
> If not, what's the process to add support for it?
There isn't really. STABS is a historic debugging format that isn't
expressive enough to support modern compilers and languages like C++.
Use DWARF 2/3/4 instead.