linux-kernel - Re: [PATCH v5 4/8] perf: build-id: name debugging vdso as "debug"

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Message-ID: <22bee274-23e1-4298-a936-50bebd802482@intel.com>
Date: Mon, 22 Jul 2024 16:21:46 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: duchangbin <changbin.du@...wei.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
 "Wanghui (OS Kernel Lab, Beijing)" <hw.huiwang@...wei.com>
Subject: Re: [PATCH v5 4/8] perf: build-id: name debugging vdso as "debug"

On 22/07/24 15:08, duchangbin wrote:
> On Thu, Jul 18, 2024 at 08:03:07PM +0300, Adrian Hunter wrote:
>> On 2/07/24 07:18, Changbin Du wrote:
>>> As normal objects, we will add debugging vdso elf to build-id cache later.
>>> Here we name the debugging one as "debug".
>>>
>>> Signed-off-by: Changbin Du <changbin.du@...wei.com>
>>> ---
>>>  tools/perf/util/build-id.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
>>> index 83a1581e8cf1..15530af2bad9 100644
>>> --- a/tools/perf/util/build-id.c
>>> +++ b/tools/perf/util/build-id.c
>>> @@ -259,8 +259,8 @@ static bool build_id_cache__valid_id(char *sbuild_id)
>>>  static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso,
>>>  					    bool is_debug)
>>>  {
>>> -	return is_kallsyms ? "kallsyms" : (is_vdso ? "vdso" : (is_debug ?
>>> -	    "debug" : "elf"));
>>> +	return is_kallsyms ? "kallsyms" : (is_debug ? "debug" : (is_vdso ?
>>> +		"vdso" : "elf"));
>>>  }
>>>  
>>>  char *__dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
>>
>> To actually add "debug", this also needs:
>>
>> diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
>> index 15530af2bad9..b5bd02a1ad0f 100644
>> --- a/tools/perf/util/build-id.c
>> +++ b/tools/perf/util/build-id.c
>> @@ -701,7 +701,7 @@ build_id_cache__add(const char *sbuild_id, const char *name, const char *realnam
>>  	 * file itself may not be very useful to users of our tools without a
>>  	 * symtab.
>>  	 */
>> -	if (!is_kallsyms && !is_vdso &&
>> +	if (!is_kallsyms &&
>>  	    strncmp(".ko", name + strlen(name) - 3, 3)) {
>>  		debugfile = build_id_cache__find_debug(sbuild_id, nsi, root_dir);
>>  		if (debugfile) {
>>
>>
>>
> This is done by later patch named "perf: build-id: try to search debugging vdso
> and add to cache". I split the changes into two patches.

With the above, the split is more functionally logical:
	1. Add support for build-id cache vdso debug
	2. For vdso, extend build_id_cache__find_debug() to find
	local kernel build files

> 
>> With that perf will populated the "debug" entry in the build-id cache.
>> Currently, when adding to the build-id cache, perf only looks in
>> /usr/lib/debug/.build-id (refer build_id_cache__find_debug()), for
>> example:
>>
>>
>> $ sudo ln -s /lib/modules/6.9.2-local/build/arch/x86/entry/vdso/vdso64.so.dbg /usr/lib/debug/.build-id/cf/702469f4637840fd6ba1a8d8a628ff83253d04.debug
>> $ ls -l ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/
>> total 8
>> -rw-r--r-- 1 ahunter ahunter    0 Jul 18 13:33 probes
>> -rw------- 1 ahunter ahunter 8192 Jul 18 13:33 vdso
>> $ perf record uname
>> Linux
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.010 MB perf.data (2 samples) ]
>> $ ls -l ~/.debug/\[vdso\]/cf702469f4637840fd6ba1a8d8a628ff83253d04/
>> total 40
>> -rwxrwxr-x 2 ahunter ahunter 32760 May 27 17:42 debug
>> -rw-r--r-- 1 ahunter ahunter     0 Jul 18 13:33 probes
>> -rw------- 1 ahunter ahunter  8192 Jul 18 13:33 vdso
>>
>>
>> Note, perf will anyway find the debug object in /usr/lib/debug/.build-id
>> so the benefit is if perf-archive is used to copy from the buildid-cache
>> to take to another machine.
>>
>>
>