linux-kernel - Re: [PATCH 03/23] perf: Add ability to attach user level registers dump to sample

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Message-ID: <20120629113922.GD2110@somewhere.redhat.com>
Date:	Fri, 29 Jun 2012 13:39:25 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>, acme@...hat.com,
	mingo@...e.hu, paulus@...ba.org, cjashfor@...ux.vnet.ibm.com,
	gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
	robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 03/23] perf: Add ability to attach user level registers
 dump to sample

On Fri, Jun 29, 2012 at 01:30:12PM +0200, Jiri Olsa wrote:
> On Fri, Jun 29, 2012 at 01:23:51PM +0200, Frederic Weisbecker wrote:
> 
> SNIP
> 
> > > 
> > > well, thats basically what we have now..
> > > 
> > > when the kernel is compiled for 32 bits, the bitmask allows to store:
> > > 
> > > ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss
> > > 
> > > and when  kernel is compiled for 64 bits, the bitmask adds 64bit stuff:
> > > 
> > > ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss
> > > r8, r9, r10, r11, r12, r13, r14, r15
> > > 
> > > 
> > > - 32 bits kernel is straightforward
> > > 
> > > - for 64 bits kernel we store whatever bitmask instructs to,
> > >   regardless if we are in compat task or native 64,
> > >   user space will deal with that in post processing
> > 
> > I can think of the crazy scenario where perf itself is compat and there
> > are 64 bits apps that will be profiled by perf. It means perf must check
> > if the kernel is 32 or 64 and depending on this, request r8-r15 or not.
> > 
> > May be that's just too unlikely to matter.
> 
> hopefully ;) anyway the kernel interface stays the same in this case as well
> 
> we can add this check later when/if we deal with compat tasks

Right!
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