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Added clarification on buffer alignment.

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In v2, the lookahead_buffer was changed from requiring 4-byte alignment
to requiring 8-byte alignment. This was not documented as well as it
could be, and as FabianInostroza noted, this also implies that
lfs_malloc must provide 8-byte alignment.

To protect against this, I've also added an assert on the alignment of
both the lookahead_size and lookahead_buffer.

found by FabianInostroza and amitv87
This commit is contained in:
Christopher Haster
2019-04-09 18:07:44 -05:00
parent c2c2ce6b97
commit 1ff6432298
3 changed files with 6 additions and 3 deletions
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3
lfs.c
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@@ -3228,8 +3228,9 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
lfs_cache_zero(lfs, &lfs->pcache); lfs_cache_zero(lfs, &lfs->pcache);
// setup lookahead, must be multiple of 64-bits // setup lookahead, must be multiple of 64-bits
LFS_ASSERT(lfs->cfg->lookahead_size % 8 == 0);
LFS_ASSERT(lfs->cfg->lookahead_size > 0); LFS_ASSERT(lfs->cfg->lookahead_size > 0);
LFS_ASSERT(lfs->cfg->lookahead_size % 8 == 0 &&
(uintptr_t)lfs->cfg->lookahead_buffer % 8 == 0);
if (lfs->cfg->lookahead_buffer) { if (lfs->cfg->lookahead_buffer) {
lfs->free.buffer = lfs->cfg->lookahead_buffer; lfs->free.buffer = lfs->cfg->lookahead_buffer;
} else { } else {

5
lfs.h
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@@ -215,8 +215,9 @@ struct lfs_config {
// By default lfs_malloc is used to allocate this buffer. // By default lfs_malloc is used to allocate this buffer.
void *prog_buffer; void *prog_buffer;
// Optional statically allocated program buffer. Must be lookahead_size. // Optional statically allocated lookahead buffer. Must be lookahead_size
// By default lfs_malloc is used to allocate this buffer. // and aligned to a 64-bit boundary. By default lfs_malloc is used to
// allocate this buffer.
void *lookahead_buffer; void *lookahead_buffer;
// Optional upper limit on length of file names in bytes. No downside for // Optional upper limit on length of file names in bytes. No downside for

1
lfs_util.h
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@@ -192,6 +192,7 @@ static inline uint32_t lfs_tobe32(uint32_t a) {
uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size); uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size);
// Allocate memory, only used if buffers are not provided to littlefs // Allocate memory, only used if buffers are not provided to littlefs
// Note, memory must be 64-bit aligned
static inline void *lfs_malloc(size_t size) { static inline void *lfs_malloc(size_t size) {
#ifndef LFS_NO_MALLOC #ifndef LFS_NO_MALLOC
return malloc(size); return malloc(size);