Messages in this thread | | | From | Alexey Budankov <> | Subject | Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample | Date | Fri, 18 May 2018 10:39:42 +0300 |
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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@linux.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@linux.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@linux.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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