On Mon, Sep 17, 2012 at 2:23 AM, Wenchao Xia <xiaw...@linux.vnet.ibm.com> wrote: > δΊ 2012-9-15 2:11, Blue Swirl ει: > >> On Thu, Sep 13, 2012 at 3:49 AM, Eric Blake <ebl...@redhat.com> wrote: >>> >>> On 09/12/2012 09:33 PM, Eric Blake wrote: >>>>> >>>>> OK ,then I think >>>>> #if __GNUC__ >= 4 >>>>> .... >>>>> #else >>>>> [warn name space pollution may happen] >>>>> #endif >>>>> would be better. >>>> >>>> >>>> It may be shorter, but it is definitely not better, at least not in the >>>> current context of qemu. Using the short form will fail a -Werror >>>> build, unless you also write a patch to qemu's configure to quit >>>> supplying -Wundef during builds. But as touching configure has a bigger >>>> impact to the overall qemu project, you're going to need a lot more >>>> buy-in from other developers that -Wundef is not helping qemu gain any >>>> portability, and that it is safe to ditch it (or get enough >>>> counter-arguments from other developers why qemu insists on the >>>> anachronistic style enforced by -Wundef, at which point you must comply >>>> and use the longer form). >>> >>> >>> On second thought, this _particular_ usage will never fail a -Wundef >>> -Werror build, precisely because -Wundef is a gcc warning, which impies >>> the warning is only ever useful in the same scenarios that the __GNUC__ >>> macro is always defined (that is, __GNUC__ is undefined only on a >>> non-gcc compiler, but what non-gcc compiler supports -Wundef -Werror?). >> >> >> The library could be used by a project that does not use GCC or pick >> CFLAGS from QEMU configuration. Supporting for example MSVC or C++ >> users for the library could be interesting one day, even if we didn't >> support MSVC or C++ at all for building the rest of QEMU. >> > Each compiler would have its own predefined macro, so I think now > I can just support gcc and give a warning when gcc not found. If > more compiler is needed, extend the macro in the future.
Yes, that's OK for now. It's also possible that any interest for non-GCC compilation or C++ will never materialize. But please support -Wundef. > > >>> >>> But why should this line be the one exemption to the rules? Either qemu >>> insists on the -Wundef style of coding (and you should use the long form >>> to conform to that style, on the off-chance that someone ever wants to >>> port to a non-gcc compiler, even in this one place where gcc can't warn >>> you about the violation of that style), or we should change the qemu >>> style (at which point, the short form is nicer here, but it also implies >>> the potential for cleaning up lots of other places to also use short >>> forms and rely on preprocessor 0 computation). >>> >>> -- >>> Eric Blake ebl...@redhat.com +1-919-301-3266 >>> Libvirt virtualization library http://libvirt.org >>> >> > > > -- > Best Regards > > Wenchao Xia >
