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

On Fri, 2015-11-06 at 13:17 +0530, Madhavan Srinivasan wrote:

On Friday 06 November 2015 08:28 AM, Sukadev Bhattiprolu wrote:

quoted

Peter Zijlstra [peterz@infradead.org] wrote:

quoted

On Thu, Nov 05, 2015 at 02:16:15AM +0530, Madhavan Srinivasan wrote:

quoted

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.

quoted

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