Re: [PATCH v2 2/2] meson: fix CONFIG_ATOMIC128 check

[Richard Henderson <richard.henderson@linaro.org>]

On 2/28/22 10:00, marcandre.lureau@redhat.com wrote:
> -# See if 64-bit atomic operations are supported.
> -# Note that without __atomic builtins, we can only
> -# assume atomic loads/stores max at pointer size.
> -config_host_data.set('CONFIG_ATOMIC64', cc.links('''
> +atomic_test = '''
>     #include <stdint.h>
>     int main(void)
>     {
> -    uint64_t x = 0, y = 0;
> +    @0@ x = 0, y = 0;
>       y = __atomic_load_n(&x, __ATOMIC_RELAXED);
>       __atomic_store_n(&x, y, __ATOMIC_RELAXED);
>       __atomic_compare_exchange_n(&x, &y, x, 0, __ATOMIC_RELAXED, __ATOMIC_RELAXED);
>       __atomic_exchange_n(&x, y, __ATOMIC_RELAXED);
>       __atomic_fetch_add(&x, y, __ATOMIC_RELAXED);
>       return 0;
> -  }'''))
> +  }'''
> +
> +# See if 64-bit atomic operations are supported.
> +# Note that without __atomic builtins, we can only
> +# assume atomic loads/stores max at pointer size.
> +config_host_data.set('CONFIG_ATOMIC64', cc.links(atomic_test.format('uint64_t')))
>   
>   has_int128 = cc.links('''
>     __int128_t a;
> @@ -1837,15 +1839,10 @@ has_int128 = cc.links('''
>   config_host_data.set('CONFIG_INT128', has_int128)
>   
>   if has_int128
> -  has_atomic128 = cc.links('''
> -    int main(void)
> -    {
> -      unsigned __int128 x = 0, y = 0;
> -      y = __atomic_load(&x, 0);
> -      __atomic_store(&x, y, 0);
> -      __atomic_compare_exchange(&x, &y, x, 0, 0, 0);
> -      return 0;
> -    }''')
> +  # "do we have 128-bit atomics which are handled inline and specifically not
> +  # via libatomic". The reason we can't use libatomic is documented in the
> +  # comment starting "GCC is a house divided" in include/qemu/atomic128.h.
> +  has_atomic128 = cc.links(atomic_test.format('unsigned __int128'))

Nice fix.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~