1 files changed, 13 insertions, 0 deletions
diff --git a/src/pkg/runtime/atomic_386.c b/src/pkg/runtime/atomic_386.c
index 79b7cbf96..1046eb81e 100644
--- a/src/pkg/runtime/atomic_386.c
+++ b/src/pkg/runtime/atomic_386.c
@@ -30,3 +30,16 @@ runtime·xadd64(uint64 volatile* addr, int64 v)
 	}
 	return old+v;
 }
+
+#pragma textflag 7
+uint64
+runtime·xchg64(uint64 volatile* addr, uint64 v)
+{
+	uint64 old;
+
+	old = *addr;
+	while(!runtime·cas64(addr, &old, v)) {
+		// nothing
+	}
+	return old;
+}