[Qemu-devel] [PATCH v2 3/4] configure: silence glib unknown attribute __alloc_size__

[John Snow <jsnow@redhat.com>]

v2: We must test compilation with the right glib flags,
    otherwise the test compile will always fail.
    In addition, test-compile the warning flag to make
    sure we can use it.

The glib headers use GCC attributes.  Unfortunately the __GNUC__ and
__GNUC_MINOR__ version macros are also defined by clang, but clang
doesn't support the same attributes as GCC.

clang 3.5.0 does not support the __alloc_size__ attribute:

  https://github.com/llvm-mirror/clang/commit/c047507a9a79e89fc8339e074fa72822a7e7ea73

The following warning is produced:

  gstrfuncs.h:257:44: warning: unknown attribute '__alloc_size__' ignored [-Wunknown-attributes]
        G_GNUC_MALLOC G_GNUC_ALLOC_SIZE(2);
          gmacros.h:67:45: note: expanded from macro 'G_GNUC_ALLOC_SIZE'
                #define G_GNUC_ALLOC_SIZE(x) __attribute__((__alloc_size__(x)))

This patch checks whether glib headers cause warnings and disables
-Wunknown-attributes if that is the case.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/configure b/configure
index 062df84..9db53ba 100755
--- a/configure
+++ b/configure
@@ -2784,6 +2784,21 @@ if ! $pkg_config --atleast-version=2.38 glib-2.0; then
     glib_subprocess=no
 fi
 
+# Silence clang 3.5.0 warnings about glib attribute __alloc_size__ usage
+cat > $TMPC << EOF
+#include <glib.h>
+int main(void) { return 0; }
+EOF
+if ! compile_prog "$glib_cflags -Werror" "$glib_libs" ; then
+    cat > $TMPC << EOF
+    int main(void) { return 0; }
+EOF
+    if compile_prog "-Werror -Wunknown-attributes" ""; then
+        glib_cflags="-Wno-unknown-attributes $glib_cflags"
+        CFLAGS="-Wno-unknown-attributes $CFLAGS"
+    fi
+fi
+
 ##########################################
 # SHA command probe for modules
 if test "$modules" = yes; then
-- 
2.1.0