Re: [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples

Ingo Molnar
2012-07-10T09:48:52Z

* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> On Mon, 2012-07-09 at 10:55 -0700, Linus Torvalds wrote:
> > However, it is worth pointing out that sp/bp have exactly the same
> > segment base issue. So if you do stack tracing into user mode, you
> > should really do the same thing for those. And quite frankly, at that
> > point vm86 mode and the stack segment matters in other ways than just
> > the base pointer: a 16-bit stack segment acts fundamentally
> > differently from a 32-bit one. So at that point it may well make much
> > more sense to take the approach Ingo suggests, and simply not follow
> > stack frames at all.
>
> Right, so I amended the patch to ignore vm86 stacks and added
> {cs,ss}_base magic to ia32 stacks.
>
> Ingo, do you want me to do a version where I simply bail on
> everything if regs->{cs,ss} != {__USER_CS, __USER32_CS} ||
> regs->flags & VM ?

Only if it's really simple to do - out of morbid curiosity, to
compare the two diffstats and such.

Thanks,

Ingo