On 07/20/2012 12:36 AM, Hu Tao wrote:
+# define virAtomicIntGet(atomic) \ + (__extension__ ({ \ + verify (sizeof(*(atomic)) == sizeof(int)); \ + (void) (0 ? *(atomic) ^ *(atomic) : 0); \ + __sync_synchronize (); \ + (int) *(atomic); \ + }))
The `verify' lines cause building warnings:
cc1: warnings being treated as errors util/virobject.c: In function 'virClassNew': util/virobject.c:74:99: error: nested extern declaration of '_gl_verify_function2' [-Wnested-externs]
Which version of gcc?
It turns out this is a problem with any gcc older than 4.6 (that is, newer gcc with static_assert support no longer triggers this problematic nested extern). I was unable to come up with a way to avoid triggering -Wnested-externs on older gcc without creating conflicting definitions. However, it's easy to work around in libvirt. If -Wnested-externs is in effect, then restrict the use of verify(...) to the top level (outside of functions), and within functions, use this instead: (void)verify_true(...) The cast to void is unfortunately necessary to avoid a -Wall of 'statement with no effect'. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org