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fix 32-bit overflow in mi_page_start for pages ≥ 4 GiB after their page meta info (issue #1309) #1326

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Merged
daanx merged 1 commit into from
Jul 7, 2026
+7 −5
Merged

fix 32-bit overflow in mi_page_start for pages ≥ 4 GiB after their page meta info (issue #1309) #1326

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3 changes: 2 additions & 1 deletion include/mimalloc/internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -683,7 +683,8 @@ static inline size_t mi_page_block_size(const mi_page_t* page) {

// Page start
static inline uint8_t* mi_page_start(const mi_page_t* page) {
return (uint8_t*)page + (page->page_woffset * MI_SIZE_SIZE);
// multiplication must be done in `size_t`; in a 32-bit multiplication the offset wraps for pages whose blocks start 4 GiB or more after the page meta info
return (uint8_t*)page + ((size_t)page->page_woffset * MI_SIZE_SIZE);
}

static inline size_t mi_page_size(const mi_page_t* page) {
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1 change: 0 additions & 1 deletion src/arena.c
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Expand Up @@ -1608,7 +1608,6 @@ static bool mi_manage_os_memory_ex2(mi_subproc_t* subproc, void* start, size_t s
mi_memid_t memid, mi_commit_fun_t* commit_fun, void* commit_fun_arg, mi_arena_id_t* arena_id) mi_attr_noexcept
{
// checks
mi_assert(_mi_is_aligned(start, MI_ARENA_SLICE_SIZE));
mi_assert(start!=NULL);
if (arena_id != NULL) { *arena_id = _mi_arena_id_none(); }
if (start==NULL) return false;
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8 changes: 5 additions & 3 deletions test/test-api.c
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Expand Up @@ -355,9 +355,11 @@ int main(void) {
}
}

// CHECK_BODY("arena_reserve") {
// result = (0==mi_reserve_os_memory(16*MI_GiB,false,true));
// }
#if (MI_INTPTR_SIZE > 4)
CHECK_BODY("arena_reserve") {
result = (0==mi_reserve_os_memory(16*MI_GiB,false,true));
}
#endif

// ---------------------------------------------------
// Heaps
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