* [PATCH] perf tools: Allow build-id with trailing zeros
@ 2021-09-10 16:41 Namhyung Kim
2021-09-10 19:41 ` Jiri Olsa
0 siblings, 1 reply; 3+ messages in thread
From: Namhyung Kim @ 2021-09-10 16:41 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo, Jiri Olsa
Cc: Ingo Molnar, Peter Zijlstra, LKML, Andi Kleen, Ian Rogers
Current perf saves a build-id with size but old versions assumes the
size of 20. In case the build-id is less than 20 (like for MD5), it'd
fill the rest with 0s.
I saw a problem when old version of perf record saved binary in the
build-id cache and new version of perf reads the data. The symbols
should be read from the build-id cache (as the path no longer has the
same binary) but it failed due to mismatch in the build-id.
symsrc__init: build id mismatch for /home/namhyung/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf.
The build-id event in the data has 20 byte build-ids, but it saw a
different size (16) when it reads the build-id of the elf file in the
build-id cache.
$ readelf -n ~/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf
Displaying notes found in: .note.gnu.build-id
Owner Data size Description
GNU 0x00000010 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: 53e4c2f42a4c61a2d632d92a72afa08f
Let's fix this by allowing trailing zeros if the size is different.
Fixes: 39be8d0115b3 ("perf tools: Pass build_id object to dso__build_id_equal()")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/dso.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index ee15db2be2f4..0c0dd877d4e9 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1349,6 +1349,18 @@ void dso__set_build_id(struct dso *dso, struct build_id *bid)
bool dso__build_id_equal(const struct dso *dso, struct build_id *bid)
{
+ static const char zeros[BUILD_ID_SIZE];
+
+ if (dso->bid.size > bid->size && dso->bid.size == BUILD_ID_SIZE) {
+ /*
+ * For the backward compatibility, it allows a build-id has
+ * trailing zeros.
+ */
+ return !memcmp(dso->bid.data, bid->data, bid->size) &&
+ !memcmp(&dso->bid.data[bid->size], zeros,
+ dso->bid.size - bid->size);
+ }
+
return dso->bid.size == bid->size &&
memcmp(dso->bid.data, bid->data, dso->bid.size) == 0;
}
--
2.33.0.309.g3052b89438-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] perf tools: Allow build-id with trailing zeros
2021-09-10 16:41 [PATCH] perf tools: Allow build-id with trailing zeros Namhyung Kim
@ 2021-09-10 19:41 ` Jiri Olsa
2021-09-10 22:38 ` Namhyung Kim
0 siblings, 1 reply; 3+ messages in thread
From: Jiri Olsa @ 2021-09-10 19:41 UTC (permalink / raw)
To: Namhyung Kim
Cc: Arnaldo Carvalho de Melo, Ingo Molnar, Peter Zijlstra, LKML,
Andi Kleen, Ian Rogers
On Fri, Sep 10, 2021 at 09:41:50AM -0700, Namhyung Kim wrote:
> Current perf saves a build-id with size but old versions assumes the
> size of 20. In case the build-id is less than 20 (like for MD5), it'd
> fill the rest with 0s.
>
> I saw a problem when old version of perf record saved binary in the
> build-id cache and new version of perf reads the data. The symbols
> should be read from the build-id cache (as the path no longer has the
> same binary) but it failed due to mismatch in the build-id.
>
> symsrc__init: build id mismatch for /home/namhyung/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf.
>
> The build-id event in the data has 20 byte build-ids, but it saw a
> different size (16) when it reads the build-id of the elf file in the
> build-id cache.
>
> $ readelf -n ~/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf
>
> Displaying notes found in: .note.gnu.build-id
> Owner Data size Description
> GNU 0x00000010 NT_GNU_BUILD_ID (unique build ID bitstring)
> Build ID: 53e4c2f42a4c61a2d632d92a72afa08f
>
> Let's fix this by allowing trailing zeros if the size is different.
>
> Fixes: 39be8d0115b3 ("perf tools: Pass build_id object to dso__build_id_equal()")
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
> tools/perf/util/dso.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index ee15db2be2f4..0c0dd877d4e9 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -1349,6 +1349,18 @@ void dso__set_build_id(struct dso *dso, struct build_id *bid)
>
> bool dso__build_id_equal(const struct dso *dso, struct build_id *bid)
> {
> + static const char zeros[BUILD_ID_SIZE];
> +
> + if (dso->bid.size > bid->size && dso->bid.size == BUILD_ID_SIZE) {
> + /*
> + * For the backward compatibility, it allows a build-id has
> + * trailing zeros.
> + */
> + return !memcmp(dso->bid.data, bid->data, bid->size) &&
> + !memcmp(&dso->bid.data[bid->size], zeros,
> + dso->bid.size - bid->size);
we now have memchr_inv in tools, so you could use:
memchr_inv(&dso->bid.data[bid->size], 0, dso->bid.size - bid->size);
and save 20 bytes in bss ;-) other than that, nice catch
Acked-by: Jiri Olsa <jolsa@redhat.com>
thanks,
jirka
> + }
> +
> return dso->bid.size == bid->size &&
> memcmp(dso->bid.data, bid->data, dso->bid.size) == 0;
> }
> --
> 2.33.0.309.g3052b89438-goog
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] perf tools: Allow build-id with trailing zeros
2021-09-10 19:41 ` Jiri Olsa
@ 2021-09-10 22:38 ` Namhyung Kim
0 siblings, 0 replies; 3+ messages in thread
From: Namhyung Kim @ 2021-09-10 22:38 UTC (permalink / raw)
To: Jiri Olsa
Cc: Arnaldo Carvalho de Melo, Ingo Molnar, Peter Zijlstra, LKML,
Andi Kleen, Ian Rogers
Hi Jiri,
On Fri, Sep 10, 2021 at 12:41 PM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Fri, Sep 10, 2021 at 09:41:50AM -0700, Namhyung Kim wrote:
> > Current perf saves a build-id with size but old versions assumes the
> > size of 20. In case the build-id is less than 20 (like for MD5), it'd
> > fill the rest with 0s.
> >
> > I saw a problem when old version of perf record saved binary in the
> > build-id cache and new version of perf reads the data. The symbols
> > should be read from the build-id cache (as the path no longer has the
> > same binary) but it failed due to mismatch in the build-id.
> >
> > symsrc__init: build id mismatch for /home/namhyung/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf.
> >
> > The build-id event in the data has 20 byte build-ids, but it saw a
> > different size (16) when it reads the build-id of the elf file in the
> > build-id cache.
> >
> > $ readelf -n ~/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf
> >
> > Displaying notes found in: .note.gnu.build-id
> > Owner Data size Description
> > GNU 0x00000010 NT_GNU_BUILD_ID (unique build ID bitstring)
> > Build ID: 53e4c2f42a4c61a2d632d92a72afa08f
> >
> > Let's fix this by allowing trailing zeros if the size is different.
> >
> > Fixes: 39be8d0115b3 ("perf tools: Pass build_id object to dso__build_id_equal()")
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> > tools/perf/util/dso.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> > index ee15db2be2f4..0c0dd877d4e9 100644
> > --- a/tools/perf/util/dso.c
> > +++ b/tools/perf/util/dso.c
> > @@ -1349,6 +1349,18 @@ void dso__set_build_id(struct dso *dso, struct build_id *bid)
> >
> > bool dso__build_id_equal(const struct dso *dso, struct build_id *bid)
> > {
> > + static const char zeros[BUILD_ID_SIZE];
> > +
> > + if (dso->bid.size > bid->size && dso->bid.size == BUILD_ID_SIZE) {
> > + /*
> > + * For the backward compatibility, it allows a build-id has
> > + * trailing zeros.
> > + */
> > + return !memcmp(dso->bid.data, bid->data, bid->size) &&
> > + !memcmp(&dso->bid.data[bid->size], zeros,
> > + dso->bid.size - bid->size);
>
> we now have memchr_inv in tools, so you could use:
> memchr_inv(&dso->bid.data[bid->size], 0, dso->bid.size - bid->size);
>
> and save 20 bytes in bss ;-) other than that, nice catch
>
> Acked-by: Jiri Olsa <jolsa@redhat.com>
right, will update!
Thanks,
Namhyung
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2021-09-10 16:41 [PATCH] perf tools: Allow build-id with trailing zeros Namhyung Kim
2021-09-10 19:41 ` Jiri Olsa
2021-09-10 22:38 ` Namhyung Kim
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