[Qemu-devel] [PATCH 1/2] Detect and use GCC atomic builtins for locking

["Loïc Minier" <lool@dooz.org>]

---
 configure   |   17 +++++++++++++++++
 qemu-lock.h |   13 +++++++++++++
 2 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/configure b/configure
index 0a84b0e..b33f045 100755
--- a/configure
+++ b/configure
@@ -1823,6 +1823,20 @@ if compile_prog "" ""; then
 fi
 
 ##########################################
+# check if we have gcc atomic built-ins
+gcc_atomic_builtins=no
+cat > $TMPC << EOF
+int main(void) {
+    int i;
+    __sync_lock_test_and_set(&i, 1);
+    __sync_lock_release(&i);
+}
+EOF
+if compile_prog "" ""; then
+    gcc_atomic_builtins=yes
+fi
+
+##########################################
 # check if we have fdatasync
 
 fdatasync=no
@@ -2168,6 +2182,9 @@ fi
 if test "$gcc_attribute_warn_unused_result" = "yes" ; then
   echo "CONFIG_GCC_ATTRIBUTE_WARN_UNUSED_RESULT=y" >> $config_host_mak
 fi
+if test "$gcc_atomic_builtins" = "yes" ; then
+  echo "CONFIG_GCC_ATOMIC_BUILTINS=y" >> $config_host_mak
+fi
 if test "$fdatasync" = "yes" ; then
   echo "CONFIG_FDATASYNC=y" >> $config_host_mak
 fi
diff --git a/qemu-lock.h b/qemu-lock.h
index 9a3e6ac..5c8eb34 100644
--- a/qemu-lock.h
+++ b/qemu-lock.h
@@ -33,6 +33,14 @@
 
 #else
 
+#ifdef CONFIG_GCC_ATOMIC_BUILTINS
+typedef int spinlock_t;
+
+#define SPIN_LOCK_UNLOCKED 0
+
+#define resetlock(p) __sync_lock_release((p))
+#else /* CONFIG_GCC_ATOMIC_BUILTINS */
+
 #if defined(__hppa__)
 
 typedef int spinlock_t[4];
@@ -56,7 +64,11 @@ static inline void resetlock (spinlock_t *p)
 }
 
 #endif
+#endif /* !CONFIG_GCC_ATOMIC_BUILTINS */
 
+#ifdef CONFIG_GCC_ATOMIC_BUILTINS
+#define testandset(p) __sync_lock_test_and_set((p), 1)
+#else /* CONFIG_GCC_ATOMIC_BUILTINS */
 #if defined(_ARCH_PPC)
 static inline int testandset (int *p)
 {
@@ -213,6 +225,7 @@ static inline int testandset (int *p)
 #else
 #error unimplemented CPU support
 #endif
+#endif /* !CONFIG_GCC_ATOMIC_BUILTINS */
 
 #if defined(CONFIG_USER_ONLY)
 static inline void spin_lock(spinlock_t *lock)
-- 
1.7.0