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

[Paolo Bonzini]

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;

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