Re: [PATCH v1] perf record: collect user registers set jointly with dwarf stacks

[Arnaldo Carvalho de Melo]

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@xxxxxxxxxxxxxxx>
> 
> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

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?

- 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