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7435c4069a
Add a bullet point to the libperf ABI TODO explaining the code simplification benefit of widening struct perf_cpu.cpu from int16_t to int: the narrow type forces defensive truncation checks at every boundary where wider CPU indices are narrowed, and values > 32767 silently wrap to negative numbers (two's complement), bypassing bounds validation without them. Acked-by: Ian Rogers <irogers@google.com> Cc: Ian Rogers <irogers@google.com> Cc: Namhyung Kim <namhyung@kernel.org> Assisted-by: Claude:claude-opus-4.6 Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
31 lines
1.5 KiB
Plaintext
31 lines
1.5 KiB
Plaintext
Future ABI changes
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==================
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This file collects items that require a libperf ABI bump. Each entry
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should describe the current limitation, the desired end state, and the
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scope of the change so that a future ABI revision can batch them
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together.
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1. Widen struct perf_cpu.cpu from int16_t to int
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- Current limit: 32767 CPUs. No architecture exceeds this today
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(x86_64 max is 8192, arm64 is 4096), but NR_CPUS limits keep
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growing. perf clamps to INT16_MAX in set_max_cpu_num() as a
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safety net.
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- Code simplification: the int16_t forces defensive truncation
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checks at every boundary where a wider CPU index (int from
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sample->cpu, al->cpu, etc.) is narrowed into struct perf_cpu.
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Without these checks, values > 32767 silently wrap to negative
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numbers (two's complement), bypassing bounds validation.
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Widening to int eliminates this entire class of silent
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truncation bugs and removes the need for the INT16_MAX clamp
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in set_max_cpu_num().
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- Scope: struct perf_cpu is embedded everywhere — perf_cpu_map__cpu(),
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perf_cpu_map__min(), perf_cpu_map__max(), perf_cpu_map__has(), the
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for_each_cpu macros, and all internal callers. The perf_cpu_map
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internal array (RC_CHK_ACCESS(map)->map[]) stores struct perf_cpu
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directly. Widening changes the struct layout and every function
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that returns or accepts struct perf_cpu by value.
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- Migration: bump LIBPERF version in libperf.map, audit all
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sizeof(struct perf_cpu) assumptions, update perf.data
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serialization if needed.
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