Re: [libvirt] [PATCH 03/13] Rewrite virAtomic APIs using GLib's atomic ops code
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(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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