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SubjectRe: [PATCH v1] perf record: collect user registers set jointly with dwarf stacks
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Hi Arnaldo,

On 17.04.2019 18:48, Arnaldo Carvalho de Melo wrote:
> On April 17, 2019 11:40:02 AM GMT-03:00, Jiri Olsa <jolsa@redhat.com> wrote:
>> 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
>
> So we need to document that, stating that specifying a set of registers together with requesting DWARF callchains may break things.

Do you mean break callchains if omitting IP,SP,BP?
For example like this:
$ perf record -g --call-graph dwarf,1024 --user-regs=AX,BX,CX -- matrix.gcc.g.O3

~Alexey

>
> - Arnaldo
>
>
>
>
>

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