diff options
authorRich Felker <>2014-08-25 22:47:27 -0400
committerRich Felker <>2014-08-25 22:47:27 -0400
commit8d998a7b3b741304df860b5dc843826257633237 (patch)
parentf5fb20b0e934770c37093105524ea644dcaba5e2 (diff)
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).
2 files changed, 42 insertions, 0 deletions
diff --git a/include/malloc.h b/include/malloc.h
index e69de29b..35f8b19c 100644
--- a/include/malloc.h
+++ b/include/malloc.h
@@ -0,0 +1,25 @@
+#ifndef _MALLOC_H
+#define _MALLOC_H
+#ifdef __cplusplus
+extern "C" {
+#define __NEED_size_t
+#include <bits/alltypes.h>
+void *malloc (size_t);
+void *calloc (size_t, size_t);
+void *realloc (void *, size_t);
+void free (void *);
+void *valloc (size_t);
+void *memalign(size_t, size_t);
+size_t malloc_usable_size(void *);
+#ifdef __cplusplus
diff --git a/src/malloc/malloc_usable_size.c b/src/malloc/malloc_usable_size.c
new file mode 100644
index 00000000..8cccd9d8
--- /dev/null
+++ b/src/malloc/malloc_usable_size.c
@@ -0,0 +1,17 @@
+#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)