kernel.git/tools/perf/util/build-id.c, branch master

perf tools: Don't read build-ids from non-regular files

2025-11-26T18:13:38Z

Simplify the build ID reading code by removing the non-blocking option. Having to pass the correct option to this function was fragile and a mistake would result in a hang, see the linked fix. Furthermore, compressed files are always opened blocking anyway, ignoring the non-blocking option. We also don't expect to read build IDs from non-regular files. The only hits to this function that are non-regular are devices that won't be elf files with build IDs, for example "/dev/dri/renderD129". Now instead of opening these as non-blocking and failing to read, we skip them. Even if something like a pipe or character device did have a build ID, I don't think it would have worked because you need to call read() in a loop, check for -EAGAIN and handle timeouts to make non-blocking reads work. Link: https://lore.kernel.org/linux-perf-users/20251022-james-perf-fix-dso-block-v1-1-c4faab150546@linaro.org/ Signed-off-by: James Clark Signed-off-by: Namhyung Kim

perf build-id: Ensure snprintf string is empty when size is 0

2025-09-19T19:53:09Z

The string result of build_id__snprintf() is unconditionally used in places like dsos__fprintf_buildid_cb(). If the build id has size 0 then this creates a use of uninitialized memory. Add null termination for the size 0 case. A similar fix was written by Jiri Olsa in commit 6311951d4f8f28c4 ("perf tools: Initialize output buffer in build_id__sprintf") but lost in the transition to snprintf. Fixes: fccaaf6fbbc59910 ("perf build-id: Change sprintf functions to snprintf") Signed-off-by: Ian Rogers Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Howard Chu Cc: Ingo Molnar Cc: James Clark Cc: Jiri Olsa Cc: Kan Liang Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Signed-off-by: Arnaldo Carvalho de Melo

perf symbol: Add blocking argument to filename__read_build_id

2025-08-25T22:07:18Z

When synthesizing build-ids, for build ID mmap2 events, they will be added for data mmaps if -d/--data is specified. The files opened for their build IDs may block on the open causing perf to hang during synthesis. There is some robustness in existing calls to filename__read_build_id by checking the file path is to a regular file, which unfortunately fails for symlinks. Rather than adding more is_regular_file calls, switch filename__read_build_id to take a "block" argument and specify O_NONBLOCK when this is false. The existing is_regular_file checking callers and the event synthesis callers are made to pass false and thereby avoiding the hang. Fixes: 53b00ff358dc ("perf record: Make --buildid-mmap the default") Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250823000024.724394-3-irogers@google.com Signed-off-by: Namhyung Kim

perf record: Cache build-ID of hit DSOs only

2025-07-31T17:46:46Z

It post-processes samples to find which DSO has samples. Based on that info, it can save used DSOs in the build-ID cache directory. But for some reason, it saves all DSOs without checking the hit mark. Skipping unused DSOs can give some speedup especially with --buildid-mmap being default. On my idle machine, `time perf record -a sleep 1` goes down from 3 sec to 1.5 sec with this change. Fixes: e29386c8f7d71fa5 ("perf record: Add --buildid-mmap option to enable PERF_RECORD_MMAP2's build id") Reviewed-by: Arnaldo Carvalho de Melo Link: https://lore.kernel.org/r/20250731070330.57116-1-namhyung@kernel.org Signed-off-by: Namhyung Kim

perf dso: Move build_id to dso_id

2025-07-25T17:37:56Z

The dso_id previously contained the major, minor, inode and inode generation information from a mmap2 event - the inode generation would be zero when reading from /proc/pid/maps. The build_id was in the dso. With build ID mmap2 events these fields wouldn't be initialized which would largely mean the special empty case where any dso would match for equality. This isn't desirable as if a dso is replaced we want the comparison to yield a difference. To support detecting the difference between DSOs based on build_id, move the build_id out of the DSO and into the dso_id. The dso_id is also stored in the DSO so nothing is lost. Capture in the dso_id what parts have been initialized and rename dso_id__inject to dso_id__improve_id so that it is clear the dso_id is being improved upon with additional information. With the build_id in the dso_id, use memcmp to compare for equality. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-7-irogers@google.com Signed-off-by: Namhyung Kim

perf build-id: Ensure struct build_id is empty before use

2025-07-25T17:37:55Z

If a build ID is read then not all code paths may ensure it is empty before use. Initialize the build_id to be zero-ed unless there is clear initialization such as a call to build_id__init. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-6-irogers@google.com Signed-off-by: Namhyung Kim

perf build-id: Mark DSO in sample callchains

2025-07-25T17:37:55Z

Previously only the sample IP's map DSO would be marked hit for the purposes of populating the build ID cache. Walk the call chain to mark all IPs and DSOs. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-5-irogers@google.com Signed-off-by: Namhyung Kim

perf build-id: Change sprintf functions to snprintf

2025-07-25T17:37:13Z

Pass in a size argument rather than implying all build id strings must be SBUILD_ID_SIZE. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-4-irogers@google.com [ fixed some build errors ] Signed-off-by: Namhyung Kim

perf build-id: Truncate to avoid overflowing the build_id data

2025-07-24T20:50:17Z

Warning when the build_id data would be overflowed would lead to memory corruption, switch to truncation. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-3-irogers@google.com Signed-off-by: Namhyung Kim

perf tools: Fix build-id event recording

2024-12-02T20:36:20Z

The build-id events written at the end of the record session are broken due to unexpected data. The write_buildid() writes the fixed length event first and then variable length filename. But a recent change made it write more data in the padding area accidentally. So readers of the event see zero-filled data for the next entry and treat it incorrectly. This resulted in wrong kernel symbols because the kernel DSO loaded a random vmlinux image in the path as it didn't have a valid build-id. Fixes: ae39ba16554e ("perf inject: Fix build ID injection") Reported-by: Linus Torvalds Tested-by: Arnaldo Carvalho de Melo Reviewed-by: Ian Rogers Link: https://lore.kernel.org/r/Z0aRFFW9xMh3mqKB@google.com Signed-off-by: Namhyung Kim