From 29b09648d6ad0a01ffaf8ff84b30084ff8bc921a Mon Sep 17 00:00:00 2001 From: Daniel Micay Date: Tue, 16 Feb 2021 08:18:44 -0500 Subject: [PATCH] avoid undefined clz and shift in edge cases This is triggered when get_large_size_class is called with a size in the range [1,4]. This can occur with aligned_alloc(8192, size). In practice, it doesn't appear to cause any harm, but we shouldn't have any undefined behavior for well-defined usage of the API. It also occurs if the caller passes a pointer outside the slab region to free_sized but the expected size is in the range [1,4]. That usage of free_sized is already going to be considered undefined, but we should avoid undefined behavior in the caller from triggering more undefined behavior when it's avoidable. --- h_malloc.c | 1 + 1 file changed, 1 insertion(+) diff --git a/h_malloc.c b/h_malloc.c index 52a227d..b07f815 100644 --- a/h_malloc.c +++ b/h_malloc.c @@ -1178,6 +1178,7 @@ static size_t get_large_size_class(size_t size) { // 512 KiB [2560 KiB, 3 MiB, 3584 KiB, 4 MiB] // 1 MiB [5 MiB, 6 MiB, 7 MiB, 8 MiB] // etc. + size = max(size, PAGE_SIZE); size_t spacing_shift = 64 - __builtin_clzl(size - 1) - 3; size_t spacing_class = 1ULL << spacing_shift; return (size + (spacing_class - 1)) & ~(spacing_class - 1);