linux-kernel - Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample

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Message-ID: <137eab54-86df-cc7d-4618-bce49dfbc2d2@linux.intel.com>
Date:   Thu, 24 May 2018 17:37:05 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a
 sample

Hi,

On 23.05.2018 16:09, Peter Zijlstra wrote:
> On Wed, May 23, 2018 at 01:06:58PM +0300, Alexey Budankov wrote:
> 
>> Is the patch ready to be up streamed now? 
> 
> Please post a new one where you modify the comment about the syscalls
> not saving registers and ideally find the commit that made it so.

Sent v3 with adjusted comment.
As far comments become outdated quickly tried to be terse.

> 
> Also; I think Andy would appreciate a comment near the syscall code that
> refers back to this code and states what registers we rely upon being
> there (+BP for this patch).

Not sure if I can find all proper places to put comments there.
However there is PUSH_AND_CLEAR_REGS macro that is employed at system 
call implementation so it is possible to put something like this there:

.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
	/*
	 ...
	 * perf/core subsystem relies on bp register value stored 
	 * at pt_regs->bp; see arch/x86/kernel/perf_regs.c: perf_get_regs_user() 
         * for more details;
         ...
	 */

Thanks,
Alexey
> 
>