gatomic: statically assert that our assumptions hold

This code assumes that int is exactly 4 bytes, and that pointers
are either 4 or 8 bytes, on platforms with __ATOMIC_SEQ_CST.
In practice this is going to be true.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=730932

diff --git a/glib/gatomic.h b/glib/gatomic.h
index 9d04b1d..056a517 100644 (file)
--- a/glib/gatomic.h
+++ b/glib/gatomic.h
@@ -87,6 +87,9 @@ G_END_DECLS
 /* We prefer the new C11-style atomic extension of GCC if available */
 #if defined(__ATOMIC_SEQ_CST) && !defined(__clang__)
 
+/* We use __atomic_load_4, so we rely on this being true */
+G_STATIC_ASSERT (sizeof (gint) == 4);
+
 #define g_atomic_int_get(atomic) \
   (G_GNUC_EXTENSION ({                                                       \
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gint));                     \
@@ -116,6 +119,9 @@ G_END_DECLS
 
 #else /* GLIB_SIZEOF_VOID_P == 8 */
 
+/* Assume that if GLIB_SIZEOF_VOID_P is not 8, it must be 4 */
+G_STATIC_ASSERT (sizeof (gpointer) == 4);
+
 #define g_atomic_pointer_get(atomic) \
   (G_GNUC_EXTENSION ({                                                       \
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \