Re: [RFC PATCH v2] perf/x86: make perf callchain work without CONFIG_FRAME_POINTER

From: Peter Zijlstra
Date: Tue Apr 16 2019 - 13:45:38 EST

On Wed, Apr 17, 2019 at 01:39:19AM +0800, Kairui Song wrote:
> And I also think the "fake"/"real" reg is fragile, could we abuse
> another eflag (just like PERF_EFLAGS_EXACT) to indicate the regs are
> partially dumped fake registers?

Sure, the SDM seems to suggest bits 1,3,5,15 are 'available'. We've
already used 3 and 5, and I think we can use !X86_EFLAGS_FIXED to
indicate a fake regs set. Any real regs set will always have that set.