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

[Daniel P . Berrangé]

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 ?

Regards,
Daniel
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