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gh-160588: Restore the gh-123022 check in the vendored mimalloc #160589

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Merged
hugovk merged 1 commit into from
Oct 24, 2026
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gh-160588: Restore the gh-123022 check in the vendored mimalloc #160589

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16 changes: 12 additions & 4 deletions Objects/mimalloc/os.c
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Original file line number Diff line number Diff line change
Expand Up @@ -126,8 +126,12 @@ void* _mi_os_get_aligned_hint(size_t try_alignment, size_t size)
if (hint == 0 || hint > MI_HINT_MAX) { // wrap or initialize
uintptr_t init = MI_HINT_BASE;
#if (MI_SECURE>0 || MI_DEBUG==0) // security: randomize start of aligned allocations unless in debug mode
uintptr_t r = _mi_heap_random_next(mi_prim_get_default_heap());
init = init + ((MI_SEGMENT_SIZE * ((r>>17) & 0xFFFFF)) % MI_HINT_AREA); // (randomly 20 bits)*4MiB == 0 to 4TiB
mi_heap_t* heap = mi_prim_get_default_heap();
// gh-123022: default heap may not be initialized in CPython in background threads
if (mi_heap_is_initialized(heap)) {
uintptr_t r = _mi_heap_random_next(heap);
init = init + ((MI_SEGMENT_SIZE * ((r>>17) & 0xFFFFF)) % MI_HINT_AREA); // (randomly 20 bits)*4MiB == 0 to 4TiB
}
#endif
uintptr_t expected = hint + size;
mi_atomic_cas_strong_acq_rel(&aligned_base, &expected, init);
Expand Down Expand Up @@ -636,8 +640,12 @@ static uint8_t* mi_os_claim_huge_pages(size_t pages, size_t* total_size) {
// Initialize the start address after the 32TiB area
start = ((uintptr_t)32 << 40); // 32TiB virtual start address
#if (MI_SECURE>0 || MI_DEBUG==0) // security: randomize start of huge pages unless in debug mode
uintptr_t r = _mi_heap_random_next(mi_prim_get_default_heap());
start = start + ((uintptr_t)MI_HUGE_OS_PAGE_SIZE * ((r>>17) & 0x0FFF)); // (randomly 12bits)*1GiB == between 0 to 4TiB
mi_heap_t* heap = mi_prim_get_default_heap();
// gh-123022: default heap may not be initialized in CPython in background threads
if (mi_heap_is_initialized(heap)) {
uintptr_t r = _mi_heap_random_next(heap);
start = start + ((uintptr_t)MI_HUGE_OS_PAGE_SIZE * ((r>>17) & 0x0FFF)); // (randomly 12bits)*1GiB == between 0 to 4TiB
}
#endif
}
end = start + size;
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