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Date: Thu, 08 Mar 2012 10:25:19 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] vnc: Fix packed boolean struct members
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>, Stefan Hajnoczi <stefanha@gmail.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Stefan Weil <sw@weilnetz.de>

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
>