linux-kernel - Re: [PATCH 1/1] perf archive: unpack to correct dir given by perf

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Message-ID: <85253bf0-7222-4abb-a583-6c55f949e6bd@gmail.com>
Date: Wed, 24 Jul 2024 01:26:14 +0800
From: Haoze Xie <royenheart@...il.com>
To: Michael Petlan <mpetlan@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>, vmolnaro@...hat.com,
 peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 Yuan Tan <tanyuan@...ylab.org>
Subject: Re: [PATCH 1/1] perf archive: unpack to correct dir given by perf



在 2024/7/16 20:29, Michael Petlan 写道:
> On Tue, 16 Jul 2024, royenheart wrote:
>> On 2024/7/12 12:35, Namhyung Kim wrote:
>>> Hello,
>>>
>>> On Mon, Jul 08, 2024 at 02:04:31AM +0800, Haoze Xie wrote:
>>>> In perf-archive.sh, the code segment that defines 'PERF_BUILDID_DIR' is
>>>> advanced before 'unpack' operation for subsequent use, followed by a
>>>> 'mkdir' operation to ensure that the dir exists. Symbols in 'unpack' will
>>>> be extracted to correct dir given by perf.
>>>>
>>>> When '--unpack' param is appointed, the symbols are extracted to '~/.debug'
>>>> folder by default, without using 'PERF_BUILDID_DIR' given by perf. This
>>>> will cause perf to be unable to find the correct buildid's path when users
>>>> configured buildid.dir in 'perf config' or used '--buildid-dir' cli param,
>>>> since perf will read these params and put them in 'PERF_BUILDID_DIR' env.
>>>> 'perf script' and 'perf report' will use the env as the basis for buildid
>>>> indexing.
>>>
>>> Can you please add an example command line and the output for the error
>>> case?  It'd be helpful to understand the problem more intuitively.
>>>
>>>>
> 
> [...]
> 
>>
>> I have two machines A and B, I use 'perf record' and 'perf archive' to get
>> a buildid archive 'perf.data.tar.bz2' on A: 
>>
>> $ perf record -a -g -- sleep 1
>> $ perf archive
>>
>> then I transfer 'perf.data' and its buildid archive to B. On machine B, I
>> use 'perf archive' to extract the buildid:
>>
>> $ perf archive --unpack
>> $   Found target file for unpacking: ./perf.data.tar.bz2
>> $   .build-id/d1/a727ab038085dbbb50e74c812e5a6e8502e8c7
>> $   ...
>>
>> But when I use 'perf script' to view hotspots, no function names are shown:
>>
>> $ perf script
>> $   No kallsyms or vmlinux with build-id 
>> $   251c1248b97a17df394058a189dffe381169ddcd was found
>> $   perf    1770 [000] 1022235.467607:          1 cycles:P: 
>> $           ffffffff8ae9ceb6 [unknown] ([kernel.kallsyms])
>> $           ffffffff8ae15af5 [unknown] ([kernel.kallsyms])
>> $           ffffffff8ae0f83b [unknown] ([kernel.kallsyms])
>> $   ......
>>
>> The problem is, I used 'perf config' to change buildid search path before:
>>
>> $ perf config --user buildid.dir=/usr/local/symbols
>> $ cat ~/.perfconfig
>> $   # this file is auto-generated.
>> $   [buildid]
>> $           dir = /usr/local/symbols
>>
> 
> Shouldn't then perf-archive just determine the directory from perf-config
> without any additional env var?
> 
>> But 'perf archive --unpack' just extract them to '~/.debug', which makes
>> perf can't found right path to search for buildid info. If I add
>> 'buildid-dir' param to replace buildid path defined in perfconfig, problem
>> can be solved temporarily:
>>
>> $ ./perf --buildid-dir ~/.debug script
>> $   perf    1770 [000] 1022235.467607:          1 cycles:P: 
>> $           ffffffff8ae9ceb6 native_write_msr+0x6 ([kernel.kallsyms])
>> $           ffffffff8ae15af5 intel_pmu_enable_all+0x15 ([kernel.kallsyms])
>> $           ffffffff8ae0f83b x86_pmu_enable+0x1ab ([kernel.kallsyms])
>>
>> The code that determines the buildid path is in the 
>> 'util/config.c:set_buildid_dir' function, which will generate
>> 'PERF_BUILDID_DIR' var.
> 
> As above, the var seems to be a duplicate to what is already stored in
> perf-config...
> 
>>
>>
> 
> Regards,
> Michael
> 

Sorry for the delay, I read about the codes, in 'perf.c:main', it will call
'perf_config' function at first, which will call 'config:set_buildid_dir'
to set an env 'PERF_BUILDID_DIR' for external commands(including
perf-archive). Codes are:

$ // perf.c
$ int main(int argc, const char **argv) {
$   // ...
$   err = perf_config(perf_default_config, NULL);
$   // ...
$ }
$
$ ...
$ // config.c
$ void set_buildid_dir(const char *dir) {
$   if (dir)
$	    scnprintf(buildid_dir, MAXPATHLEN, "%s", dir);
$
$	/* default to $HOME/.debug */
$	if (buildid_dir[0] == '\0') {
$		char *home = getenv("HOME");
$
$		if (home) {
$			snprintf(buildid_dir, MAXPATHLEN, "%s/%s",
$				 home, DEBUG_CACHE_DIR);
$		} else {
$			strncpy(buildid_dir, DEBUG_CACHE_DIR, MAXPATHLEN-1);
$		}
$		buildid_dir[MAXPATHLEN-1] = '\0';
$	}
$	/* for communicating with external commands */
$	setenv("PERF_BUILDID_DIR", buildid_dir, 1);
$ }

Or it will set to '${HOME}/.debug'('.debug' if ${HOME} not set).
'--buildid_dir' param will override it. So perf has already read the config
for us and set the 'PERF_BUILDID_DIR' env intentionally at first. I think
it's ok to use the env for indicating where to extract.