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SubjectRe: [PATCH v3] perf record: collect user registers set jointly with dwarf stacks
Date
On 13.05.2019 22:43, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 22, 2019 at 05:37:52PM +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
>> 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=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
>>
>> IP and SP registers (dwarf_regs) are collected anayways regardless of
>> the --user-regs option value provided from the command line:
>
> So user asks for a, b and c and gets a, b, c + d and e? At the very
> least we should warn that those registers are being added to the mix,
> i.e. something like:
>
> WARNING: specified --user-regs register set doesn't include registers
> needed by also specified --call-graph=dwarf, auto adding missing
> registers (list of missing registers auto-added).

Well, let's have it like this.

~Alexey

>
> - Arnaldo
>
> P.S. Back from vacation, going thru backlog, hopefully will apply your
> perf.data compression patchkit after testing its patches one by one,
> sorry for the delay for that one (and this :))
>
>> -g call-graph dwarf,K full_regs
>> -g call-graph dwarf,K --user-regs=user_regs user_regs | dwarf_regs
>> --user-regs=user_regs user_regs
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
>> ---
>> Changes in v3:
>> - avoid changes in platform specific header files
>>
>> Changes in v2:
>> - implemented dwarf register set to avoid corrupted trace
>> when --user-regs option value omits IP,SP
>>
>> ---
>> tools/perf/util/evsel.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 84cfb9fe2fc6..e5e61ee3c6e7 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -669,6 +669,9 @@ int perf_evsel__group_desc(struct perf_evsel *evsel, char *buf, size_t size)
>> return ret;
>> }
>>
>> +#define DWARF_REGS_MASK ((1ULL << PERF_REG_IP) | \
>> + (1ULL << PERF_REG_SP))
>> +
>> static void __perf_evsel__config_callchain(struct perf_evsel *evsel,
>> struct record_opts *opts,
>> struct callchain_param *param)
>> @@ -702,7 +705,10 @@ 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 |= DWARF_REGS_MASK;
>> + else
>> + attr->sample_regs_user |= PERF_REGS_MASK;
>> attr->sample_stack_user = param->dump_size;
>> attr->exclude_callchain_user = 1;
>> } else {
>> --
>> 2.20.1
>

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