[libvirt] [PATCH] build: avoid warnings on older gcc

[Viktor Mihajlovski]

On 08/15/2012 05:29 PM, Eric Blake wrote:
> On 08/15/2012 09:24 AM, Viktor Mihajlovski wrote:
>> On 08/15/2012 12:42 AM, Eric Blake wrote:
>>> The previous patch pulled in a newer version of stat-time.h from
>>> gnulib, which tries to suppress some stupid gcc warnings (see
>>> <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54113>) by exploiting
>>> a feature of newer gcc.  But we still aim to compile on RHEL 6.3,
>>> with gcc 4.4.6 (not to mention even older devel platforms like
>>> RHEL 5), which fails to build thanks to our development -Werror.
>>>
>
>>> +++ b/m4/virt-compile-warnings.m4
>>> @@ -58,6 +58,23 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
>>>        # Gnulib's stat-time.h violates this
>>>        dontwarn="$dontwarn -Waggregate-return"
>>>
>>> +    # Gnulib uses '#pragma GCC diagnostic push' to silence some
>>> +    # warnings, but older gcc doesn't support this.
>>> +    AC_CACHE_VAL([lv_cv_gcc_pragma_push_works], [
>
> I want to use AC_CACHE_CHECK instead of AC_CACHE_VAL anyways, so I'll
> send a v2.
>
>>> +      save_CFLAGS=$CFLAGS
>>> +      CFLAGS=-Wunknown-pragmas
>
> If you change this line, does it help?
>
> CFLAGS='-Wunknown-pragmas -Werror'
>
>> Hi Eric,
>>
>> I assume this was intended to suppress errors like this here:
>>
>>    CC     libvirt_driver_storage_la-storage_backend.lo
>> cc1: warnings being treated as errors
>> In file included from ../../src/storage/storage_backend.c:59:
>> ../../gnulib/lib/stat-time.h:55: error: no previous prototype for
>> 'get_stat_atime_ns' [-Wmissing-prototypes]
>
> Yep.  And I need to mention that in my commit message.
>
>> unfortunately, even applying the patch above and rerunning bootstrap,
>> configure, make didn't help and I'm still getting the errors ... the
>> interesting thing is that pragma push seems to work...
>> I am compiling on RHEL6.2, gcc 4.4.6
>
> I'm still investigating why it worked for me.  I may have had a stale
> config.cache interfering with what I posted vs. what I tested earlier.
> Look for a v2 soon.
>

I changed to AC_CACHE_CHECK and added -Werror but
for some reason the CFLAGS won't get passed to the compilation ...

configure:53231: checking lv_cv_gcc_pragma_push_works
configure:53250: gcc -std=gnu99 -c -g -O2  conftest.c >&5
conftest.c:460: warning: expected [error|warning|ignored] after '#pragma 
GCC diagnostic'
conftest.c:461: warning: expected [error|warning|ignored] after '#pragma 
GCC diagnostic'
configure:53250: $? = 0
configure:53276: gcc -std=gnu99 -c -g -O2  conftest.c >&5
conftest.c:460: warning: expected [error|warning|ignored] after '#pragma 
GCC diagnostic'
conftest.c:461: warning: expected [error|warning|ignored] after '#pragma 
GCC diagnostic'



-- 

Mit freundlichen Grüßen/Kind Regards
    Viktor Mihajlovski

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