Enable support for GCC 11 -Wmismatched-dealloc.

To help detect common kinds of memory (and other resource) management
bugs, GCC 11 adds support for the detection of mismatched calls to
allocation and deallocation functions.  At each call site to a known
deallocation function GCC checks the set of allocation functions
the former can be paired with and, if the two don't match, issues
a -Wmismatched-dealloc warning (something similar happens in C++
for mismatched calls to new and delete).  GCC also uses the same
mechanism to detect attempts to deallocate objects not allocated
by any allocation function (or pointers past the first byte into
allocated objects) by -Wfree-nonheap-object.

This support is enabled for built-in functions like malloc and free.
To extend it beyond those, GCC extends attribute malloc to designate
a deallocation function to which pointers returned from the allocation
function may be passed to deallocate the allocated objects.  Another,
optional argument designates the positional argument to which
the pointer must be passed.

This change is the first step in enabling this extended support for
Glibc.

1 files changed, 7 insertions, 4 deletions

diff --git a/malloc/malloc.h b/malloc/malloc.h
index e9157ddfc3..c1c0896d29 100644
--- a/malloc/malloc.h
+++ b/malloc/malloc.h
@@ -56,22 +56,25 @@ __THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2));
    the same pointer that was passed to it, aliasing needs to be allowed
    between objects pointed by the old and new pointers.  */
 extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
-__THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2, 3));
+  __THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2, 3))
+  __attr_dealloc_free;
 
 /* Free a block allocated by `malloc', `realloc' or `calloc'.  */
 extern void free (void *__ptr) __THROW;
 
 /* Allocate SIZE bytes allocated to ALIGNMENT bytes.  */
 extern void *memalign (size_t __alignment, size_t __size)
-__THROW __attribute_malloc__ __attribute_alloc_size__ ((2)) __wur;
+  __THROW __attribute_malloc__ __attribute_alloc_size__ ((2)) __wur
+  __attr_dealloc_free;
 
 /* Allocate SIZE bytes on a page boundary.  */
 extern void *valloc (size_t __size) __THROW __attribute_malloc__
-     __attribute_alloc_size__ ((1)) __wur;
+     __attribute_alloc_size__ ((1)) __wur __attr_dealloc_free;
 
 /* Equivalent to valloc(minimum-page-that-holds(n)), that is, round up
    __size to nearest pagesize. */
-extern void *pvalloc (size_t __size) __THROW __attribute_malloc__ __wur;
+extern void *pvalloc (size_t __size) __THROW __attribute_malloc__
+  __wur __attr_dealloc_free;
 
 /* Underlying allocation function; successive calls should return
    contiguous pieces of memory.  */