qemu/atomic: Drop special case for unsupported compiler

Since commit efc6c070aca ("configure: Add a test for the
minimum compiler version") the minimum compiler version
required for GCC is 4.8, which has the GCC BZ#36793 bug fixed.

We can safely remove the special case introduced in commit
a281ebc11a6 ("virtio: add missing mb() on notification").

With clang 3.4, __ATOMIC_RELAXED is defined, so the chunk to
remove (which is x86-specific), isn't reached either.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201210134752.780923-2-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index c1d211a351998e67d00202b6c4bcf0f04d68c94a..8f4b3a80fbd7304b310640c09fdd88fb14c2554e 100644 (file)
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -241,23 +241,6 @@
 
 #else /* __ATOMIC_RELAXED */
 
-/*
- * We use GCC builtin if it's available, as that can use mfence on
- * 32-bit as well, e.g. if built with -march=pentium-m. However, on
- * i386 the spec is buggy, and the implementation followed it until
- * 4.3 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36793).
- */
-#if defined(__i386__) || defined(__x86_64__)
-#if !QEMU_GNUC_PREREQ(4, 4)
-#if defined __x86_64__
-#define smp_mb()    ({ asm volatile("mfence" ::: "memory"); (void)0; })
-#else
-#define smp_mb()    ({ asm volatile("lock; addl $0,0(%%esp) " ::: "memory"); (void)0; })
-#endif
-#endif
-#endif
-
-
 #ifdef __alpha__
 #define smp_read_barrier_depends()   asm volatile("mb":::"memory")
 #endif