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

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Message-ID: <0d7e5c9b27044e6eac89708d407c08fe@huawei.com>
Date: Tue, 23 Jul 2024 01:51:15 +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 Mon, Jul 22, 2024 at 04:21:46PM +0300, Adrian Hunter wrote:
> 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
>
Sounds good for me.

> > 
> >> 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