linux-kernel - Re: [PATCH 1/3] perf tests: Introduce perf_regs

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Date:	Thu, 6 Mar 2014 18:22:17 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Jean Pihet <jean.pihet@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnaldo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...nel.org>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 1/3] perf tests: Introduce perf_regs_load function on ARM

On Thu, Mar 06, 2014 at 11:33:15AM +0000, Will Deacon wrote:
> On Wed, Mar 05, 2014 at 02:17:00AM +0000, Jean Pihet wrote:
> > On 4 March 2014 12:00, Will Deacon <will.deacon@....com> wrote:
> > > On Mon, Mar 03, 2014 at 09:53:21AM +0000, Jean Pihet wrote:
> > >> +     str lr, [r0, #PC]       @ Save caller PC
> > >
> > > This isn't necessarily the `caller PC' (depending on how you define it).
> > > It's the return address, which is probably (but not always) the instruction
> > > following the branch to this function.
> > Agreed. However the perf test code expects a registers buffer filled
> > in with the caller's values.
> > I can change the comment here, is that needed?
> 
> It depends what the perf test code really expects. At the moment, you're not
> providing it with anything consistent which doesn't sound correct.

the code expects caller's PC. That is what the x86 test code
expects from perf_regs_load. We take the return IP saved by
call instruction:

ENTRY(perf_regs_load)
	...
	movq 0(%rsp), %rax
	movq %rax, IP(%rdi)
	...

jirka
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