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

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Message-ID: <8a7156281b45450ebf0511373f65afa7@huawei.com>
Date: Mon, 22 Jul 2024 12:08:56 +0000
From: duchangbin <changbin.du@...wei.com>
To: Adrian Hunter <adrian.hunter@...el.com>
CC: duchangbin <changbin.du@...wei.com>, 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 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 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.
> 
> 

-- 
Cheers,
Changbin Du