Re: [RFC PATCH] configure: Fix atomic64 test for --enable-werror on macOS

[Thomas Huth <thuth@redhat.com>]

On 16/07/2020 16.25, Daniel P. Berrangé wrote:
> On Thu, Jul 16, 2020 at 03:11:01PM +0200, Thomas Huth wrote:
>> When using --enable-werror for the macOS builders in the Cirrus-CI,
>> the atomic64 test is currently failing, and config.log shows a bunch
>> of error messages like this:
>>
>>  config-temp/qemu-conf.c:6:7: error: implicit declaration of function
>>  '__atomic_load_8' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
>>   y = __atomic_load_8(&x, 0);
>>       ^
>>  config-temp/qemu-conf.c:6:7: error: this function declaration is not a
>>  prototype [-Werror,-Wstrict-prototypes]
>>
>> Suppress the warnings to make it pass.
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  Not sure whether this is the best way to fix this issue ... thus marked
>>  as RFC.
>>  Even though the compiler warns here, the program links apparently just
>>  fine afterwards and CONFIG_ATOMIC64=y gets set in the config-host.mak
>>  file on macOS, so the 64-bit atomic operations seem to be available...
>>  Any macOS users here who could shed some light on this?
> 
> The error message refers to c99, but QEMU code standard is gnu99.
> 
> It doesn't look like we set std=gnu99 when running configure
> tests though, and I wonder if that is relevant in this case,
> given that the atomic_load* stuff is all compiler built-in.
> eg does  -std=gnu99  have any impact on the warnings ?

I've dumped the config.log from a macOS run here:

 https://cirrus-ci.com/task/4569461585870848?command=main#L1295

Looks like -std=gnu99 is used for the test already.

 Thomas