Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Eric Blake (eblake@redhat.com) wrote:
> On 01/20/2017 03:41 AM, Dr. David Alan Gilbert wrote:
> 
> >> -#define QEMU_BUILD_BUG_ON(x) \
> >> -    typedef char glue(qemu_build_bug_on__, __LINE__)[(x) ? -1 : 1] \
> >> -        __attribute__((unused))
> >> +#define QEMU_BUILD_BUG_ON_STRUCT(x) \
> >> +    struct { \
> >> +        int qemu_build_bug_on : (x) ? -1 : 1; \
> >> +    }
> > 
> > The problem with this is it can't be used as an expression, where as
> > your previous version could.
> > I've got a similar case (see previous reply) that needed an expression
> > bug-on that would evaluate to zero.
> 
> Keep reading the series - the version usable in an expression is
> QEMU_BUILD_BUG_ON_ZERO, introduced in 3/4.  Patch 2/4 is just rewriting
> the existing check, with no change in the fact that it is still a
> declaration.

Ah hmm, yeh that's OK.

Dave

> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 



--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK