diff options
Diffstat (limited to 'libc/stdlib/malloc/malloc.h')
| -rw-r--r-- | libc/stdlib/malloc/malloc.h | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/libc/stdlib/malloc/malloc.h b/libc/stdlib/malloc/malloc.h index 747e8bf9e..78232d62d 100644 --- a/libc/stdlib/malloc/malloc.h +++ b/libc/stdlib/malloc/malloc.h @@ -11,8 +11,13 @@ * Written by Miles Bader <miles@gnu.org> */ -/* The alignment we guarantee for malloc return values. */ -#define MALLOC_ALIGNMENT (__alignof__ (double)) +/* The alignment we guarantee for malloc return values. We prefer this + to be at least sizeof (size_t) bytes because (a) we have to allocate + that many bytes for the header anyway and (b) guaranteeing word + alignment can be a significant win on targets like m68k and Coldfire, + where __alignof__(double) == 2. */ +#define MALLOC_ALIGNMENT \ + __alignof__ (double __attribute_aligned__ (sizeof (size_t))) /* The system pagesize... */ extern size_t __pagesize; @@ -98,17 +103,20 @@ extern int __malloc_mmb_debug; /* The size of a malloc allocation is stored in a size_t word - MALLOC_ALIGNMENT bytes prior to the start address of the allocation: + MALLOC_HEADER_SIZE bytes prior to the start address of the allocation: +--------+---------+-------------------+ | SIZE |(unused) | allocation ... | +--------+---------+-------------------+ ^ BASE ^ ADDR - ^ ADDR - MALLOC_ALIGN + ^ ADDR - MALLOC_HEADER_SIZE */ /* The amount of extra space used by the malloc header. */ -#define MALLOC_HEADER_SIZE MALLOC_ALIGNMENT +#define MALLOC_HEADER_SIZE \ + (MALLOC_ALIGNMENT < sizeof (size_t) \ + ? sizeof (size_t) \ + : MALLOC_ALIGNMENT) /* Set up the malloc header, and return the user address of a malloc block. */ #define MALLOC_SETUP(base, size) \ |