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

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 26 Mar 2020 at 18:05, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 26/03/20 18:14, Peter Maydell wrote:
> >> +#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...
>
> That's not a problem as long as they are all functions, the macros would
> simply override the function-based implementation.

Oh yes, so it would. I think I was also vaguely thinking in terms
of FreeBSD being the leading edge of "one day most or all of our
hosts will have a full stdatomic.h", so maybe we should shift to
use-host-stdatomic-by-default, with the use of the gcc __atomic*
as the fallback at some point ?

thanks
-- PMM