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Message-ID: <7bc35ce2-d936-a8bd-c14c-6cd270e2f98d@linux.intel.com>
Date: Fri, 18 May 2018 10:39:42 +0300
From: Alexey Budankov <alexey.budankov@...ux.intel.com>
To: Andy Lutomirski <luto@...capital.net>,
Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>, 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 16.05.2018 11:42, Alexey Budankov wrote:
> Hi,
> On 15.05.2018 19:30, Andy Lutomirski wrote:
>>
>>> On May 15, 2018, at 1:08 AM, Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:
>>>
>>>
>>> Hi Andy,
>>>
>>>> On 09.05.2018 17:54, Peter Zijlstra wrote:
>>>>> On Tue, May 08, 2018 at 06:21:36PM +0300, Alexey Budankov wrote:
>>>>>
>>>>> Store user space frame-pointer value (BP register) into Perf trace
>>>>> on a sample for a process so the value becomes available when
>>>>> unwinding call stacks for functions gaining event samples.
>>>>>
>>>>> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
>>>>> ---
>>>>> arch/x86/kernel/perf_regs.c | 8 +++++++-
>>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
>>>>> index e47b2dbbdef3..8d68658eff7f 100644
>>>>> --- a/arch/x86/kernel/perf_regs.c
>>>>> +++ b/arch/x86/kernel/perf_regs.c
>>>>> @@ -156,7 +156,13 @@ void perf_get_regs_user(struct perf_regs *regs_user,
>>>>
>>>>
>>>>> * Most system calls don't save these registers, don't report them.
>>>>
>>>> ^^^ that worries me and is the reason for the '-1's below. However I
>>>> think with all the PTI rework this might no longer be true.
>>>>
>>>> The Changelog needs to state that user_regs->bp is in fact valid and
>>>> ideally point to the commits that makes it so. Also this patch should
>>>> update that comment.
>>>>
>>>> Cc Andy who keeps better track of all that than me.
>>>
>>> Are there any thoughts so far? Feedback on the matter above is highly appreciated.
>>
>> Sorry, I missed this. Can you forward the original patch? I don’t have it.
Just to make sure this and below didn't sneak out of your attention.
>
> Store user space frame-pointer value (BP register) into Perf trace
> on a sample for a process so the value becomes available when
> unwinding call stacks for functions gaining event samples.
>
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
> arch/x86/kernel/perf_regs.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
> index e47b2dbbdef3..8d68658eff7f 100644
> --- a/arch/x86/kernel/perf_regs.c
> +++ b/arch/x86/kernel/perf_regs.c
> @@ -156,7 +156,13 @@ void perf_get_regs_user(struct perf_regs *regs_user,
> * Most system calls don't save these registers, don't report them.
> */
> regs_user_copy->bx = -1;
> - regs_user_copy->bp = -1;
> + /*
> + * Store user space frame-pointer value on sample
> + * to facilitate stack unwinding for cases when
> + * user space executable code has such support
> + * enabled at compile time;
> + */
> + regs_user_copy->bp = user_regs->bp;
> regs_user_copy->r12 = -1;
> regs_user_copy->r13 = -1;
> regs_user_copy->r14 = -1;
>>> These days, system calls should save all registers, but I’m not entirely sure I want to promise that they’ll continue to do so forever.
Thanks,
Alexey
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