linux-kernel - Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a sample

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Message-ID: <20180406195310.GB9010@tassilo.jf.intel.com>
Date:   Fri, 6 Apr 2018 12:53:10 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a
 sample

On Fri, Apr 06, 2018 at 10:06:26PM +0300, Alexey Budankov wrote:
> On 06.04.2018 18:31, Andi Kleen wrote:
> >> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
> >> index e47b2dbbdef3..9284048cf5b0 100644
> >> --- a/arch/x86/kernel/perf_regs.c
> >> +++ b/arch/x86/kernel/perf_regs.c
> >> @@ -157,6 +157,15 @@ void perf_get_regs_user(struct perf_regs *regs_user,
> >>  	 */
> >>  	regs_user_copy->bx = -1;
> >>  	regs_user_copy->bp = -1;
> >> +	if (user_64bit_mode(user_regs)) {
> > 
> > Why is it 64bit only? Should work on 32bit too.
> 
> bp register is a part of i386 syscall ABI 
> (http://man7.org/linux/man-pages/man2/syscall.2.html) 
> so not sure if it will make any sense for 32bit processes. 

Both 32bit and 64bit use the same frame pointer, if they
use frame pointer.

-Andi