Re: [PATCH] qemu/atomic.h: add #ifdef guards for stdatomic.h

[Peter Maydell]

On Thu, 26 Mar 2020 at 17:01, Alex Bennée <address@hidden> wrote:
>
> Deep inside the FreeBSD netmap headers we end up including stdatomic.h
> which clashes with qemu's atomic functions which are modelled along
> the C11 standard. To avoid a massive rename lets just ifdef around the
> problem.
>
> Signed-off-by: Alex Bennée <address@hidden>
> ---
>  include/qemu/atomic.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
> index f9cd24c8994..ff72db51154 100644
> --- a/include/qemu/atomic.h
> +++ b/include/qemu/atomic.h
> @@ -208,11 +208,14 @@
>  /* Provide shorter names for GCC atomic builtins, return old value */
>  #define atomic_fetch_inc(ptr)  __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)
>  #define atomic_fetch_dec(ptr)  __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)
> +
> +#ifndef atomic_fetch_add
>  #define atomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)
>  #define atomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)
>  #define atomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)
>  #define atomic_fetch_or(ptr, n)  __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)
>  #define atomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)
> +#endif

This will work around FreeBSD's current implementation in particular,
but I don't think there's anything in the C11 spec that mandates that
atomic_fetch_add() and friends have to be macros and not simply
functions...

thanks
-- PMM