Fix endianness detection with gcc 4.6 -flto -fwhole-program

Trying to build Qt with gcc 4.6 and the -flto optimization enabled
fails at ./configure state because the endianness can't be detected.
With -flto in QMAKE_CFLAGS and -fwhole-program in QMAKE_LFLAGS_APP,
gcc 4.6 manages to compute msb_bigendian[1] == lsb_littleendian[1] at
build time and reduces main() to "return 1;", throwing away the bits
being looked for.

Treating the short[] arrays as "code" and trying to actually run them
prevents even the -fwhole-program optimizer from kicking them out, and
since the endian test isn't actually run, doesn't break anything.

Merge-request: 1130
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/config.tests/unix/endian/endiantest.cpp b/config.tests/unix/endian/endiantest.cpp
index 296f8900a1..40b2c3862d 100644
--- a/config.tests/unix/endian/endiantest.cpp
+++ b/config.tests/unix/endian/endiantest.cpp
@@ -48,9 +48,9 @@ short lsb_littleendian[] = { 0x0000, 0x654c, 0x7361, 0x5374, 0x6769, 0x696e, 0x6
 int main(int, char **)
 {
     // make sure the linker doesn't throw away the arrays
-    char *msb_bigendian_string = (char *) msb_bigendian;
-    char *lsb_littleendian_string = (char *) lsb_littleendian;
-    (void) msb_bigendian_string;
-    (void) lsb_littleendian_string;
+    void (*msb_bigendian_string)() = (void (*)())msb_bigendian;
+    void (*lsb_littleendian_string)() = (void (*)())lsb_littleendian;
+    (void)msb_bigendian_string();
+    (void)lsb_littleendian_string();
     return msb_bigendian[1] == lsb_littleendian[1];
 }