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.

diff --git a/src/malloc/malloc_usable_size.c b/src/malloc/malloc_usable_size.c
index 8cccd9d8d68b2e4fc6a230a7e9f0537a60c2353a..6743ea7752a0c44305b009c80ad7b23d153a5ac0 100644 (file)
--- a/src/malloc/malloc_usable_size.c
+++ b/src/malloc/malloc_usable_size.c
@@ -13,5 +13,5 @@ struct chunk {
 
 size_t malloc_usable_size(void *p)
 {
-       return CHUNK_SIZE(MEM_TO_CHUNK(p)) - OVERHEAD;
+       return p ? CHUNK_SIZE(MEM_TO_CHUNK(p)) - OVERHEAD : 0;
 }