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util: fix gc_alloc_size alignment

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This was only aligning the gc_block_header. The returned pointer could be
incorrectly aligned.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Fixes: 69a9b343e8 ("util: add freelist allocator with mark/sweep")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9166
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23501>
This commit is contained in:
Rhys Perry 2023-06-07 12:04:49 +01:00 • committed by Marge Bot
parent 90b8666ff2
commit 928f31a24a
1 changed files with 29 additions and 4 deletions
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33
src/util/ralloc.c
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@ -553,6 +553,7 @@ ralloc_vasprintf_rewrite_tail(char **str, size_t *start, const char *fmt,
enum gc_flags {
IS_USED = (1 << 0),
CURRENT_GENERATION = (1 << 1),
IS_PADDING = (1 << 7),
};
typedef struct
@ -565,6 +566,12 @@ typedef struct
uint16_t slab_offset;
uint8_t bucket;
uint8_t flags;
/* The last padding byte must have IS_PADDING set and is used to store the amount of padding. If
* there is no padding, the IS_PADDING bit of "flags" is unset and "flags" is checked instead.
* Because of this, "flags" must be the last member of this struct.
*/
uint8_t padding[];
} gc_block_header;
/* This structure is at the start of the slab. Objects inside a slab are
@ -618,8 +625,17 @@ struct gc_ctx {
static gc_block_header *
get_gc_header(const void *ptr)
{
gc_block_header *info = (gc_block_header *) (((char *) ptr) -
sizeof(gc_block_header));
uint8_t *c_ptr = (uint8_t *)ptr;
/* Adjust for padding added to ensure alignment of the allocation. There might also be padding
* added by the compiler into gc_block_header, but that isn't counted in the IS_PADDING byte.
*/
if (c_ptr[-1] & IS_PADDING)
c_ptr -= c_ptr[-1] & ~IS_PADDING;
c_ptr -= sizeof(gc_block_header);
gc_block_header *info = (gc_block_header *)c_ptr;
assert(info->canary == GC_CANARY);
return info;
}
@ -780,8 +796,14 @@ gc_alloc_size(gc_ctx *ctx, size_t size, size_t align)
align = MAX2(align, alignof(gc_block_header));
/* Alignment will add at most align-alignof(gc_block_header) bytes of padding to the header, and
* the IS_PADDING byte can only encode up to 127.
*/
assert((align - alignof(gc_block_header)) <= 127);
size_t header_size = align64(sizeof(gc_block_header), align);
size = align64(size, align);
size += align64(sizeof(gc_block_header), align);
size += header_size;
gc_block_header *header = NULL;
if (size <= MAX_FREELIST_SIZE) {
@ -803,7 +825,10 @@ gc_alloc_size(gc_ctx *ctx, size_t size, size_t align)
header->canary = GC_CANARY;
#endif
void *ptr = (char *)header + sizeof(gc_block_header);
uint8_t *ptr = (uint8_t *)header + header_size;
if ((header_size - 1) != offsetof(gc_block_header, flags))
ptr[-1] = IS_PADDING | (header_size - sizeof(gc_block_header));
assert(((uintptr_t)ptr & (align - 1)) == 0);
return ptr;
}