kernel/tools/perf/util/synthetic-events.c, branch linux-rolling-lts

perf synthetic-events: Fix stale build ID in module MMAP2 records

2026-03-19T15:08:20Z

[ Upstream commit 35b16a7a2c4fc458304447128b86514ce9f70f3c ] perf_event__synthesize_modules() allocates a single union perf_event and reuses it across every kernel module callback. After the first module is processed, perf_record_mmap2__read_build_id() sets PERF_RECORD_MISC_MMAP_BUILD_ID in header.misc and writes that module's build ID into the event. On subsequent iterations the callback overwrites start, len, pid, and filename for the next module but never clears the stale build ID fields or the MMAP_BUILD_ID flag. When perf_record_mmap2__read_build_id() runs for the second module it sees the flag, reads the stale build ID into a dso_id, and __dso__improve_id() permanently poisons the DSO with the wrong build ID. Every module after the first therefore receives the first module's build ID in its MMAP2 record. On a system with the sunrpc and nfsd modules loaded, this causes perf script and perf report to show [unknown] for all module symbols. The latent bug has existed since commit d9f2ecbc5e47fca7 ("perf dso: Move build_id to dso_id") introduced the PERF_RECORD_MISC_MMAP_BUILD_ID check in perf_record_mmap2__read_build_id(). Commit 53b00ff358dc75b1 ("perf record: Make --buildid-mmap the default") then exposed it to all users by making the MMAP2-with-build-ID path the default. Both commits were merged in the same series. Clear the MMAP_BUILD_ID flag and zero the build_id union before each call to perf_record_mmap2__read_build_id() so that every module starts with a clean slate. Fixes: d9f2ecbc5e47fca7 ("perf dso: Move build_id to dso_id") Reviewed-by: Ian Rogers Signed-off-by: Chuck Lever Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Ian Rogers Cc: Ingo Molnar Cc: James Clark Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: Sasha Levin

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 sample: Remove arch notion of sample parsing

2025-07-25T17:37:58Z

By definition arch sample parsing and synthesis will inhibit certain kinds of cross-platform record then analysis (report, script, etc.). Remove arch_perf_parse_sample_weight and arch_perf_synthesize_sample_weight replacing with a common implementation. Combine perf_sample p_stage_cyc and retire_lat as weight3 to capture the differing uses regardless of compiled for architecture. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-21-irogers@google.com Signed-off-by: Namhyung Kim

perf record: Make --buildid-mmap the default

2025-07-25T17:37:56Z

Support for build IDs in mmap2 perf events has been present since Linux v5.12: https://lore.kernel.org/lkml/20210219194619.1780437-1-acme@kernel.org/ Build ID mmap events don't avoid the need to inject build IDs for DSO touched by samples as the build ID cache is populated by perf record. They can avoid some cases of symbol mis-resolution caused by the file system changing from when a sample occurred and when the DSO is sought. Unlike the --buildid-mmap option, this chnage doesn't disable the build ID cache but it does disable the processing of samples looking for DSOs to inject build IDs for. To disable the build ID cache the -B (--no-buildid) option should be used. Making this option the default was raised on the list in: https://lore.kernel.org/linux-perf-users/CAP-5=fXP7jN_QrGUcd55_QH5J-Y-FCaJ6=NaHVtyx0oyNh8_-Q@mail.gmail.com/ Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-9-irogers@google.com 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: Reduce size of "size" variable

2025-07-24T20:50:17Z

Later clean up of the dso_id to include a build_id will suffer from alignment and size issues. The size can only hold up to a value of BUILD_ID_SIZE (20) and the mmap2 event uses a byte for the value. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250724163302.596743-2-irogers@google.com Signed-off-by: Namhyung Kim

libperf evsel: Rename own_cpus to pmu_cpus

2025-07-24T20:41:35Z

own_cpus is generally the cpumask from the PMU. Rename to pmu_cpus to try to make this clearer. Variable rename with no other changes. Reviewed-by: Thomas Falcon Signed-off-by: Ian Rogers Tested-by: James Clark Link: https://lore.kernel.org/r/20250719030517.1990983-7-irogers@google.com Signed-off-by: Namhyung Kim

perf events: Remove scandir in thread synthesis

2025-02-24T23:46:33Z

This avoids scanddir reading the directory into memory that's allocated and instead allocates on the stack. Acked-by: Namhyung Kim Signed-off-by: Ian Rogers Acked-by: Song Liu Link: https://lore.kernel.org/r/20250222061015.303622-6-irogers@google.com Signed-off-by: Namhyung Kim

perf sample: Make user_regs and intr_regs optional

2025-02-13T04:06:11Z

The struct dump_regs contains 512 bytes of cache_regs, meaning the two values in perf_sample contribute 1088 bytes of its total 1384 bytes size. Initializing this much memory has a cost reported by Tavian Barnes as about 2.5% when running `perf script --itrace=i0`: https://lore.kernel.org/lkml/d841b97b3ad2ca8bcab07e4293375fb7c32dfce7.1736618095.git.tavianator@tavianator.com/ Adrian Hunter replied that the zero initialization was necessary and couldn't simply be removed. This patch aims to strike a middle ground of still zeroing the perf_sample, but removing 79% of its size by make user_regs and intr_regs optional pointers to zalloc-ed memory. To support the allocation accessors are created for user_regs and intr_regs. To support correct cleanup perf_sample__init and perf_sample__exit functions are created and added throughout the code base. Signed-off-by: Ian Rogers Link: https://lore.kernel.org/r/20250113194345.1537821-1-irogers@google.com Signed-off-by: Namhyung Kim