Re: [Qemu-devel] [PATCH for-1.7] atomic.h: Fix build with clang

[Peter Maydell]

Ping! This is needed as a build-fix for MacOSX and didn't
make it into 1.7-rc0. Paolo, can I get you to review this?

I did subsequently test with a Linux clang 3.3: the patch
works OK on that but is not necessary because that clang
doesn't define __ATOMIC_SEQ_CST, presumably because
it's not recent enough. I imagine recent Linux clang still needs
this fix.

thanks
-- PMM

On 22 October 2013 10:58, Peter Maydell <address@hidden> wrote:
> clang defines __ATOMIC_SEQ_CST but its implementation of the
> __atomic_exchange() builtin differs from that of gcc. Move the
> __clang__ branch of the ifdef ladder to the top and fix its
> implementation (there is no such builtin as __sync_exchange),
> so we can compile with clang again.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> I don't have access to a Linux box with clang, so this is only
> tested on MacOSX clang, but I believe it to be both required
> and correct for all clang platforms.
>
>  include/qemu/atomic.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
> index 0aa8913..492bce1 100644
> --- a/include/qemu/atomic.h
> +++ b/include/qemu/atomic.h
> @@ -168,14 +168,14 @@
>  #endif
>
>  #ifndef atomic_xchg
> -#ifdef __ATOMIC_SEQ_CST
> +#if defined(__clang__)
> +#define atomic_xchg(ptr, i)    __sync_swap(ptr, i)
> +#elif defined(__ATOMIC_SEQ_CST)
>  #define atomic_xchg(ptr, i)    ({                           \
>      typeof(*ptr) _new = (i), _old;                          \
>      __atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
>      _old;                                                   \
>  })
> -#elif defined __clang__
> -#define atomic_xchg(ptr, i)    __sync_exchange(ptr, i)
>  #else
>  /* __sync_lock_test_and_set() is documented to be an acquire barrier only.  
> */
>  #define atomic_xchg(ptr, i)    (smp_mb(), __sync_lock_test_and_set(ptr, i))
> --
> 1.7.11.4