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SubjectRe: [PATCH v1] perf record: collect user registers set jointly with dwarf stacks
On Wed, Apr 17, 2019 at 11:35:42AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Apr 17, 2019 at 09:39:52AM +0200, Jiri Olsa escreveu:
> > On Mon, Apr 15, 2019 at 06:36:13PM +0300, Alexey Budankov wrote:
> > >
> > > When dwarf stacks are collected jointly with user specified register
> > > set using --user-regs option like below the full register context is
> > > still captured on a sample:
> > >
> > > $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP -- matrix.gcc.g.O3
> > >
> > > 188143843893585 0x6b48 [0x4f8]: PERF_RECORD_SAMPLE(IP, 0x4002): 23828/23828: 0x401236 period: 1363819 addr: 0x7ffedbdd51ac
> > > ... FP chain: nr:0
> > > ... user regs: mask 0xff0fff ABI 64-bit
> > > .... AX 0x53b
> > > .... BX 0x7ffedbdd3cc0
> > > .... CX 0xffffffff
> > > .... DX 0x33d3a
> > > .... SI 0x7f09b74c38d0
> > > .... DI 0x0
> > > .... BP 0x401260
> > > .... SP 0x7ffedbdd3cc0
> > > .... IP 0x401236
> > > .... FLAGS 0x20a
> > > .... CS 0x33
> > > .... SS 0x2b
> > > .... R8 0x7f09b74c3800
> > > .... R9 0x7f09b74c2da0
> > > .... R10 0xfffffffffffff3ce
> > > .... R11 0x246
> > > .... R12 0x401070
> > > .... R13 0x7ffedbdd5db0
> > > .... R14 0x0
> > > .... R15 0x0
> > > ... ustack: size 1024, offset 0xe0
> > > . data_src: 0x5080021
> > > ... thread: stack_test2.g.O:23828
> > > ...... dso: /root/abudanko/stacks/stack_test2.g.O3
> > >
> > > After applying the change suggested in the patch the sample data contain
> > > only user specified register values:
> > >
> > > $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP -- matrix.gcc.g.03
> > >
> > > 188368474305373 0x5e40 [0x470]: PERF_RECORD_SAMPLE(IP, 0x4002): 23839/23839: 0x401236 period: 1260507 addr: 0x7ffd3d85e96c
> > > ... FP chain: nr:0
> > > ... user regs: mask 0x1c0 ABI 64-bit
> > > .... BP 0x401260
> > > .... SP 0x7ffd3d85cc20
> > > .... IP 0x401236
> > > ... ustack: size 1024, offset 0x58
> > > . data_src: 0x5080021
> > > ... thread: stack_test2.g.O:23839
> > > ...... dso: /root/abudanko/stacks/stack_test2.g.O3
> > >
> > > Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> >
> > Acked-by: Jiri Olsa <jolsa@kernel.org>
>
> So, there are registers that are needed to do the DWARF unwinding,
> right? But at the same time, if the user says only some are needed, he
> better know what they're doing and ask for at least the registers needed
> for the unwinding process to be successfull, right?

yep, that's how understand that

jirka

>
> - Arnaldo
>
> > thanks,
> > jirka
> >
> > > ---
> > > tools/perf/util/evsel.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > index 84cfb9fe2fc6..29a223b4c699 100644
> > > --- a/tools/perf/util/evsel.c
> > > +++ b/tools/perf/util/evsel.c
> > > @@ -702,7 +702,8 @@ static void __perf_evsel__config_callchain(struct perf_evsel *evsel,
> > > if (!function) {
> > > perf_evsel__set_sample_bit(evsel, REGS_USER);
> > > perf_evsel__set_sample_bit(evsel, STACK_USER);
> > > - attr->sample_regs_user |= PERF_REGS_MASK;
> > > + if (!opts->sample_user_regs)
> > > + attr->sample_regs_user |= PERF_REGS_MASK;
> > > attr->sample_stack_user = param->dump_size;
> > > attr->exclude_callchain_user = 1;
> > > } else {
> > > --
> > > 2.20.1
> > >
>
> --
>
> - Arnaldo

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