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Address review: block-comment style and document the macOS 12+ requirement

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Reformat the malloc_getcpu Apple comment to the block style and note that the
tpidr_el0/sidt scheme requires macOS 12+: macOS 11 and earlier kept the CPU
number in tpidrro_el0's low 3 bits (now retired). Cite xnu's
__TPIDR_CPU_NUM_MASK / MACHDEP_TPIDR_CPUNUM_MASK, kept in sync with
_os_cpu_number, as the source of truth.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Raúl Marín 2026-07-08 10:36:37 +02:00 • committed by Guangli Dai
parent 5aabbc87bf
commit 82e379b8f2
1 changed files with 10 additions and 2 deletions
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12
include/jemalloc/internal/jemalloc_internal_inlines_a.h
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@ -19,9 +19,17 @@ malloc_getcpu(void) {
#elif defined(JEMALLOC_HAVE_SCHED_GETCPU)
return (malloc_cpuid_t)sched_getcpu();
#elif defined(__APPLE__)
/* No sched_getcpu() on macOS; read the CPU number like _os_cpu_number(), see
/*
* No sched_getcpu() on macOS; read the CPU number like _os_cpu_number()
* does, from the low 12 bits of tpidr_el0 (arm64) or the IDT base (x86).
* The 0xfff mask is xnu's __TPIDR_CPU_NUM_MASK, kept in sync with
* _os_cpu_number in libsyscall/os/tsd.h (the kernel counterpart is
* MACHDEP_TPIDR_CPUNUM_MASK in osfmk/arm64/machine_machdep.h):
* https://github.com/apple-oss-distributions/xnu/blob/main/libsyscall/os/tsd.h
* (it is no longer in tpidrro_el0's low bits on Apple Silicon). */
* This requires macOS 12+: on macOS 11 and earlier arm64 kept the CPU
* number in tpidrro_el0's low 3 bits instead, so it would be misread here.
* Those releases are retired by Apple, so only the current layout is handled.
*/
# if defined(__aarch64__)
uint64_t cpu;
__asm__ __volatile__("mrs %0, tpidr_el0" : "=r"(cpu));