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, 0 deletions

diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 11f01f741b..30a621ab8f 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -603,6 +603,17 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
 #  define __attr_access_none(argno)
 #endif
 
+#if __GNUC_PREREQ (11, 0)
+/* Designates dealloc as a function to call to deallocate objects
+   allocated by the declared function.  */
+# define __attr_dealloc(dealloc, argno) \
+    __attribute__ ((__malloc__ (dealloc, argno)))
+# define __attr_dealloc_free __attr_dealloc (__builtin_free, 1)
+#else
+# define __attr_dealloc(dealloc, argno)
+# define __attr_dealloc_free
+#endif
+
 /* Specify that a function such as setjmp or vfork may return
    twice.  */
 #if __GNUC_PREREQ (4, 1)