tcg: Add atomic128 helpers

Force the use of cmpxchg16b on x86_64.

Wikipedia suggests that only very old AMD64 (circa 2004) did not have
this instruction.  Further, it's required by Windows 8 so no new cpus
will ever omit it.

If we truely care about these, then we could check this at startup time
and then avoid executing paths that use it.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/qemu/int128.h b/include/qemu/int128.h
index d4c6e44331..5c9890db8b 100644
--- a/include/qemu/int128.h
+++ b/include/qemu/int128.h
@@ -2,6 +2,7 @@
 #define INT128_H
 
 #ifdef CONFIG_INT128
+#include "qemu/bswap.h"
 
 typedef __int128_t Int128;
 
@@ -137,6 +138,11 @@ static inline void int128_subfrom(Int128 *a, Int128 b)
     *a -= b;
 }
 
+static inline Int128 bswap128(Int128 a)
+{
+    return int128_make128(bswap64(int128_gethi(a)), bswap64(int128_getlo(a)));
+}
+
 #else /* !CONFIG_INT128 */
 
 typedef struct Int128 Int128;