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Re: [PATCH] i386_skip_prologue.
- From: Daniel Jacobowitz <drow at false dot org>
- To: Pedro Alves <pedro_alves at portugalmail dot pt>
- Cc: gdb-patches at sourceware dot org, Mark Kettenis <kettenis at gnu dot org>
- Date: Sat, 30 Dec 2006 15:48:26 -0500
- Subject: Re: [PATCH] i386_skip_prologue.
- References: <455EE79E.6000109@portugalmail.pt> <uveldatp9.fsf@gnu.org> <455EF845.40902@portugalmail.pt> <455F2754.5060703@portugalmail.pt> <20061118163738.GA14800@nevyn.them.org> <457B1D40.7060302@portugalmail.pt>
On Sat, Dec 09, 2006 at 08:32:00PM +0000, Pedro Alves wrote:
> The i386 targets currently don't look at line number markers
> or the symbol table at all in i386_skip_prologue.
>
> I used the attached patch to test the gcc side of the fix,
> (http://gcc.gnu.org/ml/gcc-patches/2006-12/msg00633.html)
>
> With the gcc patch above applied, this patch fixes all the runto_main issues
> on Cygwin. There are a few other FAILs related to breakpoints and main,
> but those are testsuite bugs, unrelated to this. I will send patches for
> those shortly.
As this is an i386-specific change, I'd been hoping Mark Kettenis could
take a look at it. Mark, any opinion on this?
We've been going back and forth on prologue skipping choices for a long
time now. We have at least four options, each with at least two users:
- skip_prologue_using_sal
- refine_prologue_limit
- this simple approach using line numbers, i.e. what you did
- sticking to analysis of the instructions
Aside from how difficult the analysis is, there's very little target
dependent about this. It's a shame we've got so many different ways
to do it.
Is there a general philosophy we could adopt that would apply to most
or all targets?
Here's a proposal to get us started: when skipping the prologue to
place a breakpoint or finish single stepping (skip_prologue), try to
skip to the end of the first sal. But some targets may optionally run
their prologue analyzer and make sure it doesn't see anything it
objects to - like jumps. That would mean the i386 prologue analyzer
would need to know about this new call to __main. When scanning the
prologue to build frame unwind information, ignore sals entirely.
Scan until we hit the saved PC or until we believe we understand
the entire frame.
--
Daniel Jacobowitz
CodeSourcery