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SubjectRe: [PATCH 03/23] perf: Add ability to attach user level registers dump to sample
On Wed, Jun 27, 2012 at 05:30:05PM +0200, Frederic Weisbecker wrote:
> On Wed, Jun 27, 2012 at 05:25:29PM +0200, Peter Zijlstra wrote:
> > On Wed, 2012-06-27 at 17:24 +0200, Frederic Weisbecker wrote:
> > > On Wed, Jun 27, 2012 at 05:13:44PM +0200, Stephane Eranian wrote:
> > > > On Wed, Jun 27, 2012 at 5:11 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > > > > On Tue, Jun 19, 2012 at 05:47:54PM +0200, Jiri Olsa wrote:
> > > > >> @@ -4061,6 +4105,19 @@ void perf_prepare_sample(struct perf_event_header *header,
> > > > >> }
> > > > >> header->size += size;
> > > > >> }
> > > > >> +
> > > > >> + if (sample_type & PERF_SAMPLE_REGS_USER) {
> > > > >> + /* regs dump available bool */
> > > > >> + int size = sizeof(u64);
> > > > >> +
> > > > >> + data->regs_user = perf_sample_regs_user(regs);
> > > > >> + if (data->regs_user) {
> > > > >> + u64 mask = event->attr.sample_regs_user;
> > > > >> + size += hweight64(mask) * sizeof(u64);
> > > > >> + }
> > > > >> +
> > > > >> + header->size += size;
> > > > >
> > > > > We'll need to remove the 64 bits registers for compat tasks but other than
> > > > > that, it looks ok.
> > > > You cannot do this. You cannot remove register values from under the hood.
> > > > The only way the user has to parse the sample is the sample_regs_users bitmask.
> > > > You have to return 0 for those unexisting regs for compat tasks.
> > >
> > > You mean fill unexisting reg values with 0? Yeah that works.
> >
> > What does x32 look like? Is that still reported as a compat task? If so,
> > we should record all registers and not 0 out anything.
>
> To make it simple, we could always use the x86-64 registers mask interface for everyone:
> native 32 bits kernel, compat 32 bits task, 64 bits everything. And we can't fill an x86-64
> value because we are dealing with a native/compat 32 task we just fill out the requested value
> with 0.
>
> On post processing time, userspace can know if it's dealing with 32 bits task or not anyway, so
> it knows what to skip and what is relevant.

well, thats basically what we have now..

when the kernel is compiled for 32 bits, the bitmask allows to store:

ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss

and when kernel is compiled for 64 bits, the bitmask adds 64bit stuff:

ax, bx, cx, dx, si, di, bp, sp, ip, flags, cs, ds, es, fs, gs, ss
r8, r9, r10, r11, r12, r13, r14, r15


- 32 bits kernel is straightforward

- for 64 bits kernel we store whatever bitmask instructs to,
regardless if we are in compat task or native 64,
user space will deal with that in post processing


jirka


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