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Add fbounds-safety annotations for histogram.

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Reasoning:

The `histogram` parameter in `GenerateOptimalTree`
(src/utils/huffman_encode_utils.c:170) is used as an array indexed up
to `histogram_size`. It was annotated with
`__counted_by(histogram_size)` to fix bounds-safety errors. This
required annotating the caller `VP8LCreateHuffmanTree`
(src/utils/huffman_encode_utils.c:411). However, the size of
`histogram` in `VP8LCreateHuffmanTree` depends on another parameter
(`huff_code->num_symbols`), preventing direct annotation in the
signature. Instead, a local `__bidi_indexable` pointer
(`bounded_histogram`) was forged inside `VP8LCreateHuffmanTree` using
`__unsafe_forge_bidi_indexable` with the correct size and passed to
`GenerateOptimalTree`. This also required annotating parameters
`good_for_rle` and `counts` in `OptimizeHuffmanForRle`
(src/utils/huffman_encode_utils.c:37) and forging a bounded pointer
for `buf_rle` (`bounded_buf_rle`) in `VP8LCreateHuffmanTree` to pass
to `OptimizeHuffmanForRle`.

Bug: 432511821
Change-Id: I5905ff93f4cc0a9ff03c5786b5ac20c6bfa965ff
This commit is contained in:
Arman Hasanzadeh
2025-08-19 12:34:27 -07:00
parent ed02bfa963
commit fde90a49e4
1 changed files with 20 additions and 11 deletions
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29
src/utils/huffman_encode_utils.c
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@@ -34,8 +34,11 @@ static int ValuesShouldBeCollapsedToStrideAverage(int a, int b) {
// Change the population counts in a way that the consequent
// Huffman tree compression, especially its RLE-part, give smaller output.
static void OptimizeHuffmanForRle(int length, uint8_t* const good_for_rle,
uint32_t* const counts) {
static void OptimizeHuffmanForRle(int length,
uint8_t* const WEBP_COUNTED_BY(length)
good_for_rle,
uint32_t* const WEBP_COUNTED_BY(length)
counts) {
// 1) Let's make the Huffman code more compatible with rle encoding.
int i;
for (; length >= 0; --length) {
@@ -167,12 +170,11 @@ static void SetBitDepths(const HuffmanTree* const tree,
// we are not planning to use this with extremely long blocks.
//
// See https://en.wikipedia.org/wiki/Huffman_coding
static void GenerateOptimalTree(const uint32_t* const histogram,
int histogram_size,
HuffmanTree* WEBP_BIDI_INDEXABLE tree,
static void GenerateOptimalTree(
const uint32_t* const WEBP_COUNTED_BY(histogram_size) histogram,
int histogram_size, HuffmanTree* WEBP_BIDI_INDEXABLE tree,
int tree_depth_limit,
uint8_t* WEBP_COUNTED_BY(histogram_size)
const bit_depths) {
uint8_t* WEBP_COUNTED_BY(histogram_size) const bit_depths) {
uint32_t count_min;
HuffmanTree* WEBP_BIDI_INDEXABLE tree_pool;
int tree_size_orig = 0;
@@ -416,10 +418,17 @@ void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
uint8_t* const buf_rle, HuffmanTree* const huff_tree,
HuffmanTreeCode* const huff_code) {
const int num_symbols = huff_code->num_symbols;
WEBP_UNSAFE_MEMSET(buf_rle, 0, num_symbols * sizeof(*buf_rle));
OptimizeHuffmanForRle(num_symbols, buf_rle, histogram);
uint32_t* const WEBP_BIDI_INDEXABLE bounded_histogram =
WEBP_UNSAFE_FORGE_BIDI_INDEXABLE(
uint32_t*, histogram, (size_t)num_symbols * sizeof(*histogram));
uint8_t* const WEBP_BIDI_INDEXABLE bounded_buf_rle =
WEBP_UNSAFE_FORGE_BIDI_INDEXABLE(uint8_t*, buf_rle,
(size_t)num_symbols * sizeof(*buf_rle));
memset(bounded_buf_rle, 0, num_symbols * sizeof(*buf_rle));
OptimizeHuffmanForRle(num_symbols, bounded_buf_rle, bounded_histogram);
GenerateOptimalTree(
histogram, num_symbols,
bounded_histogram, num_symbols,
WEBP_UNSAFE_FORGE_BIDI_INDEXABLE(HuffmanTree*, huff_tree,
3 * num_symbols * sizeof(*huff_tree)),
tree_depth_limit, huff_code->code_lengths);