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Message-ID: <alpine.DEB.2.11.1503061332150.25334@vincent-weaver-1.umelst.maine.edu>
Date: Fri, 6 Mar 2015 13:37:03 -0500 (EST)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: Andi Kleen <andi@...stfloor.org>
cc: Stephane Eranian <eranian@...gle.com>,
Jiri Olsa <jolsa@...hat.com>,
"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
linux-man@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Paul Mackerras <paulus@...ba.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Chuck Ebbert <cebbert.lkml@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS_INTR support
On Mon, 2 Mar 2015, Andi Kleen wrote:
> > do not enable REGS_USER and REG_INTR at the same time
> > as REGS_USER will have REG_INTR values and
> > cannot be used for user stack unwinding
>
> If that's true it would be a bug. But I doubt it.
>
> The PEBS handler sets up its own pt_regs, so they should
> be independent.
I could be wrong here, but was tracing through the code.
If you trigger a PEBS interrupt (because you have precise_ip set)
and you have both REGS_USER and REGS_INTR set, then
__intel_pmu_pebs_event()
is called from
arch/x86/kernel/cpu/perf_event_intel_ds.c
and in there it sets the regs values based solely on
if (sample_type & PERF_SAMPLE_REGS_INTR) {
}
with those values copies into regs and then passed upstream through
perf_event_overflow()
so if the sample_type has *both* PERF_SAMPLE_REGS_INTR and
PERF_SAMPLE_REGS_USER set, then the PERF_SAMPLE_REGS_USER values
will have the same register values as the PERF_SAMPLE_REGS_INTR values.
Maybe this is the expected behavior, or maybe I am missing something
still.
Vince
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