diff options
Diffstat (limited to 'newlib/libc')
| -rw-r--r-- | newlib/libc/stdlib/nano-mallocr.c | 51 |
1 files changed, 37 insertions, 14 deletions
diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c index 457eb8860..a0accdd36 100644 --- a/newlib/libc/stdlib/nano-mallocr.c +++ b/newlib/libc/stdlib/nano-mallocr.c @@ -123,19 +123,24 @@ typedef size_t malloc_size_t; typedef struct malloc_chunk { - /* ------------------ - * chunk->| size (4 bytes) | - * ------------------ - * | Padding for | - * | alignment | - * | holding neg | - * | offset to size | - * ------------------ - * mem_ptr->| point to next | - * | free when freed| - * | or data load | - * | when allocated | - * ------------------ + /* -------------------------------------- + * chunk->| size | + * -------------------------------------- + * | Padding for alignment | + * | This includes padding inserted by | + * | the compiler (to align fields) and | + * | explicit padding inserted by this | + * | implementation. If any explicit | + * | padding is being used then the | + * | sizeof (size) bytes at | + * | mem_ptr - CHUNK_OFFSET must be | + * | initialized with the negative | + * | offset to size. | + * -------------------------------------- + * mem_ptr->| When allocated: data | + * | When freed: pointer to next free | + * | chunk | + * -------------------------------------- */ /* size of the allocated payload area, including size before CHUNK_OFFSET */ @@ -187,8 +192,13 @@ extern void * nano_pvalloc(RARG size_t s); static inline chunk * get_chunk_from_ptr(void * ptr) { + /* Assume that there is no explicit padding in the + chunk, and that the chunk starts at ptr - CHUNK_OFFSET. */ chunk * c = (chunk *)((char *)ptr - CHUNK_OFFSET); - /* Skip the padding area */ + + /* c->size being negative indicates that there is explicit padding in + the chunk. In which case, c->size is currently the negative offset to + the true size. */ if (c->size < 0) c = (chunk *)((char *)c + c->size); return c; } @@ -314,6 +324,19 @@ void * nano_malloc(RARG malloc_size_t s) if (offset) { + /* Initialize sizeof (malloc_chunk.size) bytes at + align_ptr - CHUNK_OFFSET with negative offset to the + size field (at the start of the chunk). + + The negative offset to size from align_ptr - CHUNK_OFFSET is + the size of any remaining padding minus CHUNK_OFFSET. This is + equivalent to the total size of the padding, because the size of + any remaining padding is the total size of the padding minus + CHUNK_OFFSET. + + Note that the size of the padding must be at least CHUNK_OFFSET. + + The rest of the padding is not initialized. */ *(long *)((char *)r + offset) = -offset; } |