Re: [PATCH 8/8] perf test: Add file offset diagnostic test for corrupted perf.data

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Hardcoded little-endian byte sequence causes the test to fail on big-endian architectures.
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commit af35d72bcb6cca8ee9ddf5a0da66e97329974342
Author: Arnaldo Carvalho de Melo <acme@redhat.com>

perf test: Add file offset diagnostic test for corrupted perf.data

This commit adds a shell test to verify that file_offset diagnostic messages
work correctly when perf encounters corrupted events. It intentionally
corrupts an MMAP2 event's size field in a recorded perf.data file and checks
that perf report produces a warning message that includes the file offset.

> diff --git a/tools/perf/tests/shell/data_file_offset_diagnostics.sh b/tools/perf/tests/shell/data_file_offset_diagnostics.sh
> new file mode 100755
> --- /dev/null
> +++ b/tools/perf/tests/shell/data_file_offset_diagnostics.sh

[ ... ]

> +# Copy the file and corrupt the MMAP2 event's size field.
> +# perf_event_header layout: type(u32) misc(u16) size(u16)
> +# Set size to 16 (0x10 0x00 little-endian) — below the MMAP2
> +# minimum, which triggers the "event size too small" warning.
> +cp "${perfdata}" "${corrupted}"
> +printf '\x10\x00' | dd of="${corrupted}" bs=1 seek=$((mmap2_offset_dec + 6)) conv=notrunc 2>/dev/null

[Severity: Medium]
Will this hardcoded little-endian byte sequence cause the test to fail on
big-endian architectures?

The test explicitly overwrites the 16-bit size field of a PERF_RECORD_MMAP2
event using the bytes \x10\x00. Since perf.data files are natively encoded
in the host system's byte order, on big-endian hosts (e.g., s390x) the
native u16 parsing of 0x10 at offset 0 and 0x00 at offset 1 will evaluate
to 0x1000 (4096).

Because 4096 exceeds the minimum MMAP2 event size, the internal validation
check is bypassed. This will cause perf report to skip 4096 bytes and
attempt to parse unaligned garbage data instead of emitting the expected
"too small" warning for the MMAP2 event.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260602235709.1541603-1-acme@kernel.org?part=8