[PATCH v2 0/1] perf: Set build-id using build-id header on new mmap records

[PATCH v2 0/1] perf: Set build-id using build-id header on new mmap records

[James Clark]

Changes since v1:
 * Add read lock around dso find
 * Bracket style fix

Hi,

We are seeing an issue with doing Coresight decode off target where
initially the correct dso from ~/.debug is used, but after a new thread
in the perf.data file is passed with its mmap record, the local version
of the dso is picked up instead. This happens if the binary exists in the
same path on both devices, for example /bin/ls.

Initially when parsing the build-ids in the header, the dso for /bin/ls
will be created, and the file will correctly point to
~/.debug/bin/ls/2f15ad836be3339dec0e2e6a3c637e08e48aacbd/elf, but for any
new threads or mmaps that are also for /bin/ls, they will not have a
build-id set so they point to /bin/ls on the local machine rather than the
debug folder.

To fix this I made it possible to look up which existing dsos have
build id's set that originate from the header and then copy that build-id
onto the new dso if the name matches. Another way to do it would
be to stop comparing the mmap id so it matches on filename only, but I
think we do want to differentiate between different mmaps, even if they
have the same name, which is how it works in this version.

Applies to perf/core 56dce8681

James Clark (1):
  perf: Set build-id using build-id header on new mmap records

 tools/perf/util/dso.h    |  1 +
 tools/perf/util/header.c |  1 +
 tools/perf/util/map.c    | 20 +++++++++++++++++---
 3 files changed, 19 insertions(+), 3 deletions(-)

-- 
2.28.0

[PATCH v2 1/1] perf: Set build-id using build-id header on new mmap records

[James Clark]

MMAP records that occur after the build-id header is parsed do not have
their build-id set even if the filename matches an entry from the
header. Set the build-id on these dsos as long as the MMAP record
doesn't have its own build-id set.

This fixes an issue with off target analysis where the local version of
a dso is loaded rather than one from ~/.debug via a build-id.

Reported-by: Denis Nikitin <denik@chromium.org>
Signed-off-by: James Clark <james.clark@arm.com>
---
 tools/perf/util/dso.h    |  1 +
 tools/perf/util/header.c |  1 +
 tools/perf/util/map.c    | 20 +++++++++++++++++---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 011da3924fc1..3a9fd4d389b5 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -167,6 +167,7 @@ struct dso {
 	enum dso_load_errno	load_errno;
 	u8		 adjust_symbols:1;
 	u8		 has_build_id:1;
+	u8		 header_build_id:1;
 	u8		 has_srcline:1;
 	u8		 hit:1;
 	u8		 annotate_warned:1;
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 6da12e522edc..571d73d4f976 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2200,6 +2200,7 @@ static int __event_process_build_id(struct perf_record_header_build_id *bev,
 
 		build_id__init(&bid, bev->data, size);
 		dso__set_build_id(dso, &bid);
+		dso->header_build_id = 1;
 
 		if (dso_space != DSO_SPACE__USER) {
 			struct kmod_path m = { .name = NULL, };
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 1803d3887afe..e0aa4a254583 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -127,7 +127,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
 
 	if (map != NULL) {
 		char newfilename[PATH_MAX];
-		struct dso *dso;
+		struct dso *dso, *header_bid_dso;
 		int anon, no_dso, vdso, android;
 
 		android = is_android_lib(filename);
@@ -183,9 +183,23 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
 		}
 		dso->nsinfo = nsi;
 
-		if (build_id__is_defined(bid))
+		if (build_id__is_defined(bid)) {
 			dso__set_build_id(dso, bid);
-
+		} else {
+			/*
+			 * If the mmap event had no build ID, search for an existing dso from the
+			 * build ID header by name. Otherwise only the dso loaded at the time of
+			 * reading the header will have the build ID set and all future mmaps will
+			 * have it missing.
+			 */
+			down_read(&machine->dsos.lock);
+			header_bid_dso = __dsos__find(&machine->dsos, filename, false);
+			up_read(&machine->dsos.lock);
+			if (header_bid_dso && header_bid_dso->header_build_id) {
+				dso__set_build_id(dso, &header_bid_dso->bid);
+				dso->header_build_id = 1;
+			}
+		}
 		dso__put(dso);
 	}
 	return map;
-- 
2.28.0

Re: [PATCH v2 0/1] perf: Set build-id using build-id header on new mmap records

[Jiri Olsa]

On Fri, Mar 04, 2022 at 09:09:55AM +0000, James Clark wrote:
> Changes since v1:
>  * Add read lock around dso find
>  * Bracket style fix
> 
> Hi,
> 
> We are seeing an issue with doing Coresight decode off target where
> initially the correct dso from ~/.debug is used, but after a new thread
> in the perf.data file is passed with its mmap record, the local version
> of the dso is picked up instead. This happens if the binary exists in the
> same path on both devices, for example /bin/ls.
> 
> Initially when parsing the build-ids in the header, the dso for /bin/ls
> will be created, and the file will correctly point to
> ~/.debug/bin/ls/2f15ad836be3339dec0e2e6a3c637e08e48aacbd/elf, but for any
> new threads or mmaps that are also for /bin/ls, they will not have a
> build-id set so they point to /bin/ls on the local machine rather than the
> debug folder.
> 
> To fix this I made it possible to look up which existing dsos have
> build id's set that originate from the header and then copy that build-id
> onto the new dso if the name matches. Another way to do it would
> be to stop comparing the mmap id so it matches on filename only, but I
> think we do want to differentiate between different mmaps, even if they
> have the same name, which is how it works in this version.
> 
> Applies to perf/core 56dce8681
> 
> James Clark (1):
>   perf: Set build-id using build-id header on new mmap records

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> 
>  tools/perf/util/dso.h    |  1 +
>  tools/perf/util/header.c |  1 +
>  tools/perf/util/map.c    | 20 +++++++++++++++++---
>  3 files changed, 19 insertions(+), 3 deletions(-)
> 
> -- 
> 2.28.0
> 

Re: [PATCH v2 0/1] perf: Set build-id using build-id header on new mmap records

[Arnaldo Carvalho de Melo]

Em Sat, Mar 05, 2022 at 09:33:59PM +0100, Jiri Olsa escreveu:
> On Fri, Mar 04, 2022 at 09:09:55AM +0000, James Clark wrote:
> > Changes since v1:
> >  * Add read lock around dso find
> >  * Bracket style fix
> > 
> > Hi,
> > 
> > We are seeing an issue with doing Coresight decode off target where
> > initially the correct dso from ~/.debug is used, but after a new thread
> > in the perf.data file is passed with its mmap record, the local version
> > of the dso is picked up instead. This happens if the binary exists in the
> > same path on both devices, for example /bin/ls.
> > 
> > Initially when parsing the build-ids in the header, the dso for /bin/ls
> > will be created, and the file will correctly point to
> > ~/.debug/bin/ls/2f15ad836be3339dec0e2e6a3c637e08e48aacbd/elf, but for any
> > new threads or mmaps that are also for /bin/ls, they will not have a
> > build-id set so they point to /bin/ls on the local machine rather than the
> > debug folder.
> > 
> > To fix this I made it possible to look up which existing dsos have
> > build id's set that originate from the header and then copy that build-id
> > onto the new dso if the name matches. Another way to do it would
> > be to stop comparing the mmap id so it matches on filename only, but I
> > think we do want to differentiate between different mmaps, even if they
> > have the same name, which is how it works in this version.
> > 
> > Applies to perf/core 56dce8681
> > 
> > James Clark (1):
> >   perf: Set build-id using build-id header on new mmap records
> 
> Acked-by: Jiri Olsa <jolsa@kernel.org>

Thanks, applied.

- Arnaldo