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, 11 insertions, 5 deletions

diff --git a/stdlib/stdlib.h b/stdlib/stdlib.h
index 6360845d98..0481c12355 100644
--- a/stdlib/stdlib.h
+++ b/stdlib/stdlib.h
@@ -550,6 +550,9 @@ extern void *calloc (size_t __nmemb, size_t __size)
 extern void *realloc (void *__ptr, size_t __size)
      __THROW __attribute_warn_unused_result__ __attribute_alloc_size__ ((2));
 
+/* Free a block allocated by `malloc', `realloc' or `calloc'.  */
+extern void free (void *__ptr) __THROW;
+
 #ifdef __USE_MISC
 /* Re-allocate the previously allocated block in PTR, making the new
    block large enough for NMEMB elements of SIZE bytes each.  */
@@ -558,11 +561,13 @@ extern void *realloc (void *__ptr, size_t __size)
    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));
-#endif
+     __attribute_alloc_size__ ((2, 3))
+    __attr_dealloc_free;
 
-/* Free a block allocated by `malloc', `realloc' or `calloc'.  */
-extern void free (void *__ptr) __THROW;
+/* Add reallocarray as its own deallocator.  */
+extern void *reallocarray (void *__ptr, size_t __nmemb, size_t __size)
+     __THROW __attr_dealloc (reallocarray, 1);
+#endif
 
 #ifdef __USE_MISC
 # include <alloca.h>
@@ -788,7 +793,8 @@ extern int system (const char *__command) __wur;
 /* Return a malloc'd string containing the canonical absolute name of the
    existing named file.  */
 extern char *canonicalize_file_name (const char *__name)
-     __THROW __nonnull ((1)) __wur;
+     __THROW __nonnull ((1)) __attribute_malloc__
+     __attr_dealloc_free __wur;
 #endif
 
 #if defined __USE_MISC || defined __USE_XOPEN_EXTENDED