linux-kernel - Re: [PATCH v2 7/8] perf dso: Move build_id to dso

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Message-ID: <aA_fYvTI7YRIy2k9@google.com>
Date: Mon, 28 Apr 2025 13:04:50 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Athira Rajeev <atrajeev@...ux.ibm.com>,
	Kajol Jain <kjain@...ux.ibm.com>, Li Huafei <lihuafei1@...wei.com>,
	"Steinar H. Gunderson" <sesse@...gle.com>,
	James Clark <james.clark@...aro.org>,
	Stephen Brennan <stephen.s.brennan@...cle.com>,
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Zhongqiu Han <quic_zhonhan@...cinc.com>,
	Yicong Yang <yangyicong@...ilicon.com>,
	Krzysztof Łopatowski <krzysztof.m.lopatowski@...il.com>,
	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Zixian Cai <fzczx123@...il.com>,
	Steve Clevenger <scclevenger@...amperecomputing.com>,
	Thomas Falcon <thomas.falcon@...el.com>,
	Martin Liska <martin.liska@....com>,
	Martin Liška <m.liska@...link.cz>,
	Song Liu <song@...nel.org>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/8] perf dso: Move build_id to dso_id

On Fri, Apr 25, 2025 at 11:46:40AM -0700, Ian Rogers wrote:
> On Fri, Apr 25, 2025 at 10:15 AM Namhyung Kim <namhyung@...nel.org> wrote:
> > On Thu, Apr 24, 2025 at 12:58:30PM -0700, Ian Rogers wrote:
[SNIP]
> > > @@ -1665,18 +1675,20 @@ bool dso__build_id_equal(const struct dso *dso, struct build_id *bid)
> > >  void dso__read_running_kernel_build_id(struct dso *dso, struct machine *machine)
> > >  {
> > >       char path[PATH_MAX];
> > > +     struct build_id bid;
> > >
> > >       if (machine__is_default_guest(machine))
> > >               return;
> > >       sprintf(path, "%s/sys/kernel/notes", machine->root_dir);
> > > -     if (sysfs__read_build_id(path, dso__bid(dso)) == 0)
> > > -             dso__set_has_build_id(dso);
> > > +     sysfs__read_build_id(path, &bid);
> > > +     dso__set_build_id(dso, &bid);
> >
> > Why not check the return value anymore?
> 
> Checking the return value was a mistake. For example if we have
> libc.so with a build ID and then it is replaced with a libc.so without
> a build ID then build ID wouldn't be updated previously as reading the
> build ID had failed - no value found.

I'm not sure if it updates the dso as a whole.  This functions is to get
build-ID of the kernel and it seems we can skip this if it already has a
build-ID.  But if sysfs__read_build_id() failed, it may have a garbage.

Do I miss something?

Thanks,
Namhyung

> >
> > >  }
> > >
> > >  int dso__kernel_module_get_build_id(struct dso *dso,
> > >                                   const char *root_dir)
> > >  {
> > >       char filename[PATH_MAX];
> > > +     struct build_id bid;
> > >       /*
> > >        * kernel module short names are of the form "[module]" and
> > >        * we need just "module" here.
> > > @@ -1687,9 +1699,8 @@ int dso__kernel_module_get_build_id(struct dso *dso,
> > >                "%s/sys/module/%.*s/notes/.note.gnu.build-id",
> > >                root_dir, (int)strlen(name) - 1, name);
> > >
> > > -     if (sysfs__read_build_id(filename, dso__bid(dso)) == 0)
> > > -             dso__set_has_build_id(dso);
> > > -
> > > +     sysfs__read_build_id(filename, &bid);
> > > +     dso__set_build_id(dso, &bid);
> > >       return 0;
> > >  }