Messages in this thread | | | Date | Tue, 11 Mar 2014 19:25:11 +0100 | Subject | Re: [PATCH 1/3] perf tests: Introduce perf_regs_load function on ARM | From | Jean Pihet <> |
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HI Will, Steve,
On 6 March 2014 18:22, Jiri Olsa <jolsa@redhat.com> wrote: > On Thu, Mar 06, 2014 at 11:33:15AM +0000, Will Deacon wrote: >> On Wed, Mar 05, 2014 at 02:17:00AM +0000, Jean Pihet wrote: >> > On 4 March 2014 12:00, Will Deacon <will.deacon@arm.com> wrote: >> > > On Mon, Mar 03, 2014 at 09:53:21AM +0000, Jean Pihet wrote: >> > >> + str lr, [r0, #PC] @ Save caller PC >> > > >> > > This isn't necessarily the `caller PC' (depending on how you define it). >> > > It's the return address, which is probably (but not always) the instruction >> > > following the branch to this function. >> > Agreed. However the perf test code expects a registers buffer filled >> > in with the caller's values. >> > I can change the comment here, is that needed? >> >> It depends what the perf test code really expects. At the moment, you're not >> providing it with anything consistent which doesn't sound correct. > > the code expects caller's PC. That is what the x86 test code > expects from perf_regs_load. We take the return IP saved by > call instruction: > > ENTRY(perf_regs_load) > ... > movq 0(%rsp), %rax > movq %rax, IP(%rdi) > ... > > jirka
The perf built-in test code expects the caller PC to do the unwinding from. Does that sound correct to you?
Do you want me to add a note like this one (as done in the upcoming aarch64 patches, to be submitted asap after testing): " /* * Implementation of void perf_regs_load(u64 *regs); * * This functions fills in the 'regs' buffer from the actual registers values. * * Notes: * 1. the return value of the pc is retrieved from lr and stored, in order * to skip the call to this function, * 2. the current value of lr is merely retrieved and stored because the * value before the call to this function is unknown at this time; it will * be unwound from the dwarf information in unwind__get_entries. */ "
Please let me know how to make this better.
Regards, Jean
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