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

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Message-ID: <14afba8e-cb85-4d7d-96e4-d65fd8ebc2d5@intel.com>
Date: Thu, 18 Jul 2024 20:03:07 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Changbin Du <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>
Cc: 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-kernel@...r.kernel.org,
 llvm@...ts.linux.dev, Hui Wang <hw.huiwang@...wei.com>
Subject: Re: [PATCH v5 4/8] perf: build-id: name debugging vdso as "debug"

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) {



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.