The -Wextra flag bundle gained a new warning -Wcast-function-type. This complains if you cast between two function prototypes where the number of parameters or their data types are not compatible. Unfortunately we need such "bad" function casts for our event callbacks. It is possible to silence the warning by first casting to the generic "void (*)(void)" function prototype, but that is rather ugly to add throughout libvirt code. Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; --- Pushed as a CI build fix m4/virt-compile-warnings.m4 | 3 +++ 1 file changed, 3 insertions(+) diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4 index 0cf67fa..cbd9e0c 100644 --- a/m4/virt-compile-warnings.m4 +++ b/m4/virt-compile-warnings.m4 @@ -151,6 +151,9 @@ AC_DEFUN([LIBVIRT_GLIB_COMPILE_WARNINGS],[ # that one off, so we need to manually enable this again wantwarn="$wantwarn -Wjump-misses-init" + # We do "bad" function casts all the time for event callbacks + wantwarn="$wantwarn -Wno-cast-function-type" + # GNULIB turns on -Wformat=2 which implies -Wformat-nonliteral, # so we need to manually re-exclude it. Also, older gcc 4.2 # added an implied ATTRIBUTE_NONNULL on any parameter marked -- 2.14.3