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

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct
Date: Thu, 19 Jan 2017 15:26:55 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 01/19/2017 03:07 PM, Michael S. Tsirkin wrote:
> There are theoretical concerns that some compilers might not trigger
> build failures on attempts to define an array of size -1 and make it a
> variable sized array instead.

Rather, the concern is that if someone changes code so that the 'x' of
QEMU_BUILD_BUG_ON(x) is no longer a compile time constant, we want a
compile-time failure rather than a runtime variable-sized array that may
or may not crash.

> Let rewrite using a struct with a negative
> bit field size instead as there are no dynamic bit field sizes.  This is
> similar to what Linux does.
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  include/qemu/compiler.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

I don't know if you want to tweak the commit wording, but I'm okay with
the patch itself.

Reviewed-by: Eric Blake <address@hidden>

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

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