linux-kernel - Re: [PATCH v5] perf record: collect user registers set jointly with dwarf stacks

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Date:   Fri, 31 May 2019 09:27:38 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] perf record: collect user registers set jointly with
 dwarf stacks


On 30.05.2019 22:41, Arnaldo Carvalho de Melo wrote:
> Em Thu, May 30, 2019 at 10:03:36PM +0300, Alexey Budankov escreveu:
>>
>> When dwarf stacks are collected jointly with user specified register
>> set using --user-regs option like below the full register context is
>> captured on a sample:
>>
>>   $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP -- stack_test2.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. IP and SP registers (DWARF_MINIMAL_REGS)
>> are collected anyways regardless of the --user-regs value provided from
>> the command line:
> 
> Applied, changed the subject and description to:
> 
> perf record: Allow mixing --user-regs with --call-graph=dwarf
> 
> When DWARF stacks were requested and at the same time that the user
> specifies a register set using the --user-regs option the full register
> context was being captured on samples:
> 
>   $ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP -- stack_test2.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
> 
> I.e. the --user-regs=IP,SP,BP was being ignored, being overridden by the
> needs of --call-graph=dwarf.
> 
> After applying the change in this patch the sample data contains the
> user specified register, but making sure that at least the minimal set
> of register needed for DWARF unwinding (DWARF_MINIMAL_REGS) is
> requested.
> 
> The user is warned that DWARF unwinding may not work if extra registers
> end up being needed.
> 
>   -g call-graph dwarf,K                         full_regs
>   --user-regs=user_regs                         user_regs
>   -g call-graph dwarf,K --user-regs=user_regs   user_regs + DWARF_MINIMAL_REGS
> <REST remains the same>
> 

Sounds better. Thanks!

~Alexey