musl/src/malloc/malloc_usable_size.c

#include <malloc.h>

void *(*const __realloc_dep)(void *, size_t) = realloc;

struct chunk {
	size_t psize, csize;
	struct chunk *next, *prev;
};

#define OVERHEAD (2*sizeof(size_t))
#define CHUNK_SIZE(c) ((c)->csize & -2)
#define MEM_TO_CHUNK(p) (struct chunk *)((char *)(p) - OVERHEAD)

size_t malloc_usable_size(void *p)
{
	return p ? CHUNK_SIZE(MEM_TO_CHUNK(p)) - OVERHEAD : 0;
}
add malloc_usable_size function and non-stub malloc.h this function is needed for some important practical applications of ABI compatibility, and may be useful for supporting some non-portable software at the source level too. I was hesitant to add a function which imposes any constraints on malloc internals; however, it turns out that any malloc implementation which has realloc must already have an efficient way to determine the size of existing allocations, so no additional constraint is imposed. for now, some internal malloc definitions are duplicated in the new source file. if/when malloc is refactored to put them in a shared internal header file, these could be removed. since malloc_usable_size is conventionally declared in malloc.h, the empty stub version of this file was no longer suitable. it's updated to provide the standard allocator functions, nonstandard ones (even if stdlib.h would not expose them based on the feature test macros in effect), and any malloc-extension functions provided (currently, only malloc_usable_size). 12 years ago			`#include <malloc.h>`

			`void (const __realloc_dep)(void *, size_t) = realloc;`

			`struct chunk {`
			`size_t psize, csize;`
			`struct chunk next, prev;`
			`};`

			`#define OVERHEAD (2*sizeof(size_t))`
			`#define CHUNK_SIZE(c) ((c)->csize & -2)`
			`#define MEM_TO_CHUNK(p) (struct chunk )((char )(p) - OVERHEAD)`

			`size_t malloc_usable_size(void *p)`
			`{`
fix malloc_usable_size for NULL input the linux man page specifies malloc_usable_size(0) to return 0 and this is the semantics other implementations follow (jemalloc). reported by Alexander Monakov. 10 years ago			`return p ? CHUNK_SIZE(MEM_TO_CHUNK(p)) - OVERHEAD : 0;`
add malloc_usable_size function and non-stub malloc.h this function is needed for some important practical applications of ABI compatibility, and may be useful for supporting some non-portable software at the source level too. I was hesitant to add a function which imposes any constraints on malloc internals; however, it turns out that any malloc implementation which has realloc must already have an efficient way to determine the size of existing allocations, so no additional constraint is imposed. for now, some internal malloc definitions are duplicated in the new source file. if/when malloc is refactored to put them in a shared internal header file, these could be removed. since malloc_usable_size is conventionally declared in malloc.h, the empty stub version of this file was no longer suitable. it's updated to provide the standard allocator functions, nonstandard ones (even if stdlib.h would not expose them based on the feature test macros in effect), and any malloc-extension functions provided (currently, only malloc_usable_size). 12 years ago			`}`