shared/glib: reimplement g_atomic_pointer_compare_and_exchange() macro

With glib 2.63.2 and clang 9.0.0 (Fedora 32) we get compile errors:

  ../clients/cloud-setup/nmcs-provider-ec2.c:51:8: error: incompatible pointer types passing 'typeof ((((void *)0))) *' (aka 'void **') to parameter of type 'const char **' [-Werror,-Wincompatible-pointer-types]
                  if (!g_atomic_pointer_compare_and_exchange (&base_cached, NULL, base))
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /usr/include/glib-2.0/glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
      __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                             ^~~~~~~~~~~~~~
  ../src/devices/bluetooth/nm-bluez-manager.c:2836:2: error: incompatible pointer types passing 'typeof ((((void *)0))) *' (aka 'void **') to parameter of type 'const NMBtVTableNetworkServer **' (aka 'const struct _NMBtVTableNetworkServer **') [-Werror,-Wincompatible-pointer-types]
          g_atomic_pointer_compare_and_exchange (&nm_bt_vtable_network_server, NULL, &priv->vtable_network_server);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /usr/include/glib-2.0/glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
      __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                             ^~~~~~~~~~~~~~
  ../src/devices/bluetooth/nm-bluez-manager.c:2853:2: error: passing 'typeof ((&priv->vtable_network_server)) *' (aka 'struct _NMBtVTableNetworkServer **') to parameter of type 'const NMBtVTableNetworkServer **' (aka 'const struct _NMBtVTableNetworkServer **') discards qualifiers in nested pointer types [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
          g_atomic_pointer_compare_and_exchange (&nm_bt_vtable_network_server, &priv->vtable_network_server, NULL);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /usr/include/glib-2.0/glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
      __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                             ^~~~~~~~~~~~~~
  ../src/devices/nm-device.c:8857:8: error: incompatible pointer types passing 'typeof ((((void *)0))) *' (aka 'void **') to parameter of type 'GBytes **' (aka 'struct _GBytes **') [-Werror,-Wincompatible-pointer-types]
                  if (!g_atomic_pointer_compare_and_exchange (&global_duid, NULL, p)) {
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /usr/include/glib-2.0/glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
      __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                             ^~~~~~~~~~~~~~

The issue happens because glib passes the "atomic" argument to

  __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)

without cast, and clang 9 seems to be picky about const pointers.
Add our own version of the macro that does better casts while also having
better compile time checks for valid arguments.

1 files changed, 26 insertions, 0 deletions

diff --git a/shared/nm-glib-aux/nm-glib.h b/shared/nm-glib-aux/nm-glib.h
index fa44f316c8..dfb75bf05f 100644
--- a/shared/nm-glib-aux/nm-glib.h
+++ b/shared/nm-glib-aux/nm-glib.h
@@ -575,4 +575,30 @@ _nm_g_value_unset (GValue *value)
 
 /*****************************************************************************/
 
+/* Glib implements g_atomic_pointer_compare_and_exchange() as a macro.
+ * For one, to inline the atomic operation and also to perform some type checks
+ * on the arguments.
+ * Depending on compiler and glib version, glib passes the arguments as they
+ * are to __atomic_compare_exchange_n(). Some clang version don't accept const
+ * pointers there. Reimplement the macro to get that right, but with stronger
+ * type checks (as we use typeof()). Had one job. */
+static inline gboolean
+_g_atomic_pointer_compare_and_exchange (volatile void *atomic,
+                                        gconstpointer oldval,
+                                        gconstpointer newval)
+{
+	return g_atomic_pointer_compare_and_exchange ((void **) atomic, (void *) oldval, (void *) newval);
+}
+#undef g_atomic_pointer_compare_and_exchange
+#define g_atomic_pointer_compare_and_exchange(atomic, oldval, newval) \
+	({ \
+		typeof (atomic) const _atomic = (atomic); \
+		typeof (*_atomic) const _oldval = (oldval); \
+		typeof (*_atomic) const _newval = (newval); \
+		\
+		_g_atomic_pointer_compare_and_exchange (_atomic, _oldval, _newval); \
+	})
+
+/*****************************************************************************/
+
 #endif  /* __NM_GLIB_H__ */