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LibC: Adjust malloc size classes to ensure 8-byte aligned pointers

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The pointers returned by malloc should always be 8-byte aligned on x86.
We were not consistent about this, as some ChunkedBlock size classes
were not divisible by 8.

This fixes some OOB reads found by running GCC in UE.
This commit is contained in:
Andreas Kling
2020-11-13 10:56:30 +01:00
parent df3a70eac2
commit 3a2727844c
1 changed files with 2 additions and 2 deletions
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4
Libraries/LibC/malloc.cpp
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@@ -75,7 +75,7 @@ static bool s_log_malloc = false;
static bool s_scrub_malloc = true;
static bool s_scrub_free = true;
static bool s_profiling = false;
static unsigned short size_classes[] = { 8, 16, 32, 64, 128, 252, 508, 1016, 2036, 4090, 8188, 16376, 32756, 0 };
static unsigned short size_classes[] = { 8, 16, 32, 64, 128, 256, 500, 1016, 2032, 4088, 8184, 16376, 32752, 0 };
static constexpr size_t num_size_classes = sizeof(size_classes) / sizeof(unsigned short);
struct MallocStats {
@@ -144,7 +144,7 @@ struct ChunkedBlock
ChunkedBlock* m_prev { nullptr };
ChunkedBlock* m_next { nullptr };
FreelistEntry* m_freelist { nullptr };
unsigned short m_free_chunks { 0 };
size_t m_free_chunks { 0 };
[[gnu::aligned(8)]] unsigned char m_slot[0];
void* chunk(size_t index)