Re: [Qemu-trivial] [Qemu-devel] [PATCH] vnc: Fix packed boolean struct members

[Anthony Liguori]

On 03/08/2012 10:08 AM, Paolo Bonzini wrote:
> Il 08/03/2012 16:26, Stefan Hajnoczi ha scritto:
> > I had to drop this patch from the trivial patches tree, it tickles a
> > new gcc warning.  Please resend with the necessary change.
> >
> > I cannot reproduce it on my build host here with gcc Debian 4.6.2-12
> > but Anthony reports the following Ubuntu/Linaro 4.5.2-8ubuntu4:
> >
> >    CC    ui/vnc-auth-sasl.o
> > cc1: warnings being treated as errors
> > /home/anthony/git/qemu/ui/vnc-auth-sasl.c: In function
> > ‘vnc_sasl_client_cleanup’:
> > /home/anthony/git/qemu/ui/vnc-auth-sasl.c:34:9: error: suggest
> > parentheses around assignment used as truth value
> > make: *** [ui/vnc-auth-sasl.o] Error 1
>
> Looks like a GCC bug where
>
>     x = y = 0;
>
> is converted to
>
>     x = (y = 0) != 0;

Curious, why convert like this?  What does this optimization do?

Regards,

Anthony Liguori

> and the magic that does this inside the compiler causes the warning.
>
> We should add a configure check to only add -Werror on compilers newer
> than X (for example X could leave out GCC 4.5), so that this patch can
> be reapplied.
>
> Paolo