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, 35 insertions, 0 deletions

diff --git a/libio/tst-wmemstream1.c b/libio/tst-wmemstream1.c
index f8b308b..f80655b 100644
--- a/libio/tst-wmemstream1.c
+++ b/libio/tst-wmemstream1.c
@@ -1,5 +1,40 @@
 #include <wchar.h>
 
+extern int fclose (FILE*);
+
+#if defined __GNUC__ && __GNUC__ >= 11
+/* Verify that calling fclose on the result of open_wmemstream doesn't
+   trigger GCC -Wmismatched-dealloc with fclose forward-declared and
+   without <stdio.h> included first (it is included later, in.
+   "tst-memstream1.c").  */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic error "-Wmismatched-dealloc"
+#endif
+
+int test_open_wmemstream_no_stdio (void)
+{
+  {
+    wchar_t *buf;
+    size_t size;
+    FILE *f = open_wmemstream (&buf, &size);
+    fclose (f);
+  }
+
+  {
+    FILE* (*pf)(wchar_t**, size_t*) = open_wmemstream;
+    wchar_t *buf;
+    size_t size;
+    FILE *f = pf (&buf, &size);
+    fclose (f);
+  }
+  return 0;
+}
+
+#if defined __GNUC__ && __GNUC__ >= 11
+/* Restore -Wmismatched-dealloc setting.  */
+# pragma GCC diagnostic pop
+#endif
+
 #define CHAR_T wchar_t
 #define W(o) L##o
 #define OPEN_MEMSTREAM open_wmemstream