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Re: [PATCH, RFC] MIPS: Implement the getcontext API
- From: Ralf Baechle <ralf at linux-mips dot org>
- To: David Daney <ddaney at caviumnetworks dot com>
- Cc: Daniel Jacobowitz <dan at debian dot org>, Brian Foster <brian dot foster at innova-card dot com>, "Maciej W. Rozycki" <macro at codesourcery dot com>, linux-mips at linux-mips dot org, libc-ports at sourceware dot org, "Maciej W. Rozycki" <macro at linux-mips dot org>
- Date: Thu, 2 Apr 2009 15:29:36 +0200
- Subject: Re: [PATCH, RFC] MIPS: Implement the getcontext API
- References: <alpine.DEB.1.10.0902282326580.4064@tp.orcam.me.uk> <49AD6139.60209@caviumnetworks.com> <200903040919.29294.brian.foster@innova-card.com> <20090304121732.GA28381@caradoc.them.org> <49AEAE1D.5030205@caviumnetworks.com>
On Wed, Mar 04, 2009 at 08:36:45AM -0800, David Daney wrote:
>> That won't quite retain the ABI: you need to make sure everyone
>> locates it by using the stack pointer instead of the return pc.
>> Fortunately, GCC uses the return PC only for instruction matching
>> today. I have a vague memory it used to use the stack pointer but
>> this was more reliable.
>
> That is correct. Due to various errata the trampoline cannot always be
> at a fixed offset to the signal context bits. So we had to use the
> return PC as you indicate.
To maintaine compatibility with old debuggers and possibly other software
that knows about the stackframe layout I wrote the signal code to only
use the larger alignment of the stackframe if a particular processor
requires it.
However one possible improvment would be to change the way a struct sigframe
or rt_sigframe is allocated on the stack such that not the beginning of
the structure is aligned but the rs_code field is kept aligned. Would
such a change cause problems for gdb?
Ralf