Re: [Qemu-devel] [PATCH v2] libvixl: a64: Skip "-Wunused-variable" for gcc 5.0.0 or higher

[Eric Blake <eblake@redhat.com>]

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On 10/12/2014 01:50 AM, Peter Maydell wrote:
> On 12 October 2014 01:32, Chen Gang <gang.chen.5i5j@gmail.com> wrote:
>> On 10/12/14 5:25, Peter Maydell wrote:
>>> Some other approaches to this that would confine the
>>> fix to the makefiles rather than requiring us to modify
>>> the vixl source itself:
>>>  a) add a -Wno- option for the affected .o files
>>
>> It is one way, but may have effect with gcc 4 version, and also it is
>> effect with the whole file which is wider than current way.
>>
>>>  b) use -isystem rather than -I to include the libvixl
>>>     directory on the include path
>>>
>>
>> It sounds good to me, although for me, it is not related with current
>> issue.
> 
> -isystem disables a bunch of gcc warnings automatically,
> which is why I suggested it. I'm not overall sure it's
> a great idea though.

-isystem is a heavy hammer, affecting the entire compilation.  Better
might be just marking the ONE header as being a system header (silence
various warnings caused by just that header, while still letting the
rest of the compilation warn).  If the header comes from third-party
sources, this is probably the best approach.  It is done by adding:

#if __GNUC__ >= 3
#pragma GCC system_header
#endif

to the header that would otherwise trigger warnings.

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


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