Re: [RFC PATCH 0/3]perf/core: extend perf_reg and perf_sample_regs_intr

[Michael Ellerman]

On Fri, 2015-11-06 at 13:17 +0530, Madhavan Srinivasan wrote:
> On Friday 06 November 2015 08:28 AM, Sukadev Bhattiprolu wrote:
> > Peter Zijlstra [peterz@xxxxxxxxxxxxx] wrote:
> > > On Thu, Nov 05, 2015 at 02:16:15AM +0530, Madhavan Srinivasan wrote:
> > > > Second patch updates struct arch_misc_reg for arch/powerpc with pmu registers
> > > > and adds offsetof macro for the same. It extends perf_reg_value()
> > > > to use reg idx to decide on struct to return value from.
> > > 
> > > Why; what's in those regs?
> > 
> > Those are PMU control registers/counters (in Patch 2) that are of
> > interest only in the context of a PMU interrupt and not relevant
> > to ptrace itself.
> 
> Yes. Thats right.

> > Could we add those registers to 'struct pt_regs' anyway?
> 
> I would prefer not to. Since as you mentioned, these are
> not relevant to ptrace. Currently patch 2, adds only few
> pmu registers, but would like to include more.

You can't just add them to pt_regs, it's part of the userspace ABI.

We could define a kernel internal version of pt_regs, but I don't think we want
to for this.

If we did that would bloat pt_regs for all users in the kernel, when we really
only want these regs for perf.

cheers

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