linux-kernel - Re: [PATCH 2/3] perf unwind-libdw: Handle JIT-generated DSOs properly

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Message-ID: <CAM9d7chc9uyj-gZT0_a6aca6UMqjiXGNiSB8MGUXchg5VGrKrw@mail.gmail.com>
Date:   Wed, 13 Dec 2023 14:13:57 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org,
        Milian Wolff <milian.wolff@...b.com>,
        Pablo Galindo <pablogsal@...il.com>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH 2/3] perf unwind-libdw: Handle JIT-generated DSOs properly

On Tue, Dec 12, 2023 at 10:07 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Mon, Dec 11, 2023 at 11:05 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > Usually DSOs are mapped from the beginning of the file, so the base
> > address of the DSO can be calculated by map->start - map->pgoff.
> >
> > However, JIT DSOs which are generated by `perf inject -j`, are mapped
> > only the code segment.  This makes unwind-libdw code confusing and
> > rejects processing unwinds in the JIT DSOs.  It should use the map
> > start address as base for them to fix the confusion.
> >
> > Fixes: 1fe627da3033 ("perf unwind: Take pgoff into account when reporting elf to libdwfl")
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> >  tools/perf/util/unwind-libdw.c | 21 +++++++++++++++++----
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> > index 8554db3fc0d7..6013335a8dae 100644
> > --- a/tools/perf/util/unwind-libdw.c
> > +++ b/tools/perf/util/unwind-libdw.c
> > @@ -46,6 +46,7 @@ static int __report_module(struct addr_location *al, u64 ip,
> >  {
> >         Dwfl_Module *mod;
> >         struct dso *dso = NULL;
> > +       Dwarf_Addr base;
> >         /*
> >          * Some callers will use al->sym, so we can't just use the
> >          * cheaper thread__find_map() here.
> > @@ -58,13 +59,25 @@ static int __report_module(struct addr_location *al, u64 ip,
> >         if (!dso)
> >                 return 0;
> >
> > +       /*
> > +        * The generated JIT DSO files only map the code segment without
> > +        * ELF headers.  Since JIT codes used to be packed in a memory
> > +        * segment, calculating the base address using pgoff falls into
> > +        * a different code in another DSO.  So just use the map->start
> > +        * directly to pick the correct one.
> > +        */
> > +       if (!strncmp(dso->long_name, "/tmp/jitted-", 12))
>
> Perhaps it would be better to test:
> dso->symtab_type == DSO_BINARY_TYPE__JAVA_JIT

Well.. it's a little different.  The JAVA_JIT type files have
"/tmp/perf-" prefix and it's a plain text file (for symbols).
While this is an ELF file generated by `perf inject -j`.

Thanks,
Namhyung