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

[Frederic Weisbecker <fweisbec@gmail.com>]

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.