linux-kernel - Re: [PATCH 04/15] perf: Add ability to dump user regs

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Message-ID: <20120328161043.GI17189@somewhere.redhat.com>
Date:	Wed, 28 Mar 2012 18:10:45 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>, acme@...hat.com,
	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, eranian@...gle.com,
	gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
	rostedt@...dmis.org, robert.richter@....com,
	linux-kernel@...r.kernel.org, mjw@...hat.com
Subject: Re: [PATCH 04/15] perf: Add ability to dump user regs

On Wed, Mar 28, 2012 at 06:01:56PM +0200, Jiri Olsa wrote:
> On Wed, Mar 28, 2012 at 11:12:30AM -0400, Frank Ch. Eigler wrote:
> > Hi, Jiri -
> > 
> > > [...]
> > > > [...]  Upon a normal syscall entry to the kernel, not
> > > > all user registers are saved explicitly for such easy retrieval.  The
> > > > others may be spilled to the stack by gcc during the various sys_*
> > > > functions or elsewhere.  [...]
> > > 
> > > Are you reffering to x86_64 where only portion of registers
> > > is stored by SAVE_ARGS macro? Seems like 32 bits stores the
> > > whole pt_regs.
> > 
> > I believe that's the right area.  I'm not sure even the 32-bit variant
> > is complete enough, for example exempting MMX/SSE registers.  These
> > may also contain spilled registers before long.
> 
> right, I covered only general registers... need to check about mmc/sse

I think you can forget that. At least for now.

I believe in most cases you'll only need rsp for the unwinding. Then on some
tricky frame setups you might need more general registers values but I guess
this shouldn't be too frequent.

But you won't need MMX/SSE.
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