linux-kernel - Re: [PATCH v6] perf: __kmod_path__parse: deal with kernel module names in '[]' correctly.

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Date:	Tue, 21 Apr 2015 17:28:51 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	<jolsa@...hat.com>, <acme@...nel.org>, <jolsa@...nel.org>,
	<mingo@...hat.com>, <lizefan@...wei.com>, <pi3orama@....com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6] perf: __kmod_path__parse: deal with kernel module
 names in '[]' correctly.

On 2015/4/21 13:16, Namhyung Kim wrote:
> Hi Wang,
> 
> On Tue, Apr 21, 2015 at 03:33:10AM +0000, Wang Nan wrote:
>> Before patch ba92732e9808df679ddf75c5ea1c0caae6d7dce2 ('perf kmaps:
>> Check kmaps to make code more robust'), perf report and perf annotate
>> will segfault if trace data contains kernel module information like
>> this:
>>
>>  # perf report -D -i ./perf.data
>>  ...
>>  0 0 0x188 [0x50]: PERF_RECORD_MMAP -1/0: [0xffffffbff1018000(0xf068000) @ 0]: x [test_module]
>>  ...
>>
>>  # perf report -i ./perf.data --objdump=/path/to/objdump --kallsyms=/path/to/kallsyms
>>
>>  perf: Segmentation fault
>>  -------- backtrace --------
>>  /path/to/perf[0x503478]
>>  /lib64/libc.so.6(+0x3545f)[0x7fb201f3745f]
>>  /path/to/perf[0x499b56]
>>  /path/to/perf(dso__load_kallsyms+0x13c)[0x49b56c]
>>  /path/to/perf(dso__load+0x72e)[0x49c21e]
>>  /path/to/perf(map__load+0x6e)[0x4ae9ee]
>>  /path/to/perf(thread__find_addr_map+0x24c)[0x47deec]
>>  /path/to/perf(perf_event__preprocess_sample+0x88)[0x47e238]
>>  /path/to/perf[0x43ad02]
>>  /path/to/perf[0x4b55bc]
>>  /path/to/perf(ordered_events__flush+0xca)[0x4b57ea]
>>  /path/to/perf[0x4b1a01]
>>  /path/to/perf(perf_session__process_events+0x3be)[0x4b428e]
>>  /path/to/perf(cmd_report+0xf11)[0x43bfc1]
>>  /path/to/perf[0x474702]
>>  /path/to/perf(main+0x5f5)[0x42de95]
>>  /lib64/libc.so.6(__libc_start_main+0xf4)[0x7fb201f23bd4]
>>  /path/to/perf[0x42dfc4]
>>
>> This is because __kmod_path__parse treats '[' leading names as kernel
>> name instead of names of kernel module. If perf.data contains build
>> information and the buildid of such modules can be found, the DSO of
>> it will be treated as kernel, not kernel module.
> 
> Sorry if I missed some prior discussion on it, but any chance to treat
> them as modules instead of kernel binaries?
> 
> Thanks,
> Namhyung
> 
> 

Sorry, I tried but failed to understand your question. What this patch do
is to treat them as modules instead of kernel binaries (or binary?
since kernel is a whole binary and kernel modules are DSOs).

[SNIP]

>> +	/* path            alloc_name  alloc_ext  kmod  comp   name             ext */
>> +	T("[test_module]", true      , true     , true, false, "[test_module]", NULL);
>> +	T("[test_module]", false     , true     , true, false, NULL           , NULL);
>> +	T("[test_module]", true      , false    , true, false, "[test_module]", NULL);
>> +	T("[test_module]", false     , false    , true, false, NULL           , NULL);
>> +	M("[test_module]", PERF_RECORD_MISC_CPUMODE_UNKNOWN, true);
>> +	M("[test_module]", PERF_RECORD_MISC_KERNEL, true);
>> +	M("[test_module]", PERF_RECORD_MISC_USER, false);

Before this patch, these testcases will return kmod == false result.

Thanks.

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