1 files changed, 39 insertions, 0 deletions
diff --git a/pkg/syncevent/waiter_noasm_unsafe.go b/pkg/syncevent/waiter_noasm_unsafe.go
new file mode 100644
index 000000000..1c4b0e39a
--- /dev/null
+++ b/pkg/syncevent/waiter_noasm_unsafe.go
@@ -0,0 +1,39 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// waiterUnlock is called from g0, so when the race detector is enabled,
+// waiterUnlock must be implemented in assembly since no race context is
+// available.
+//
+// +build !race
+// +build !amd64,!arm64
+
+package syncevent
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// waiterUnlock is the "unlock function" passed to runtime.gopark by
+// Waiter.Wait*. wg is &Waiter.g, and g is a pointer to the calling runtime.g.
+// waiterUnlock returns true if Waiter.Wait should sleep and false if sleeping
+// should be aborted.
+//
+//go:nosplit
+func waiterUnlock(g unsafe.Pointer, wg *unsafe.Pointer) bool {
+	// The only way this CAS can fail is if a call to Waiter.NotifyPending()
+	// has replaced *wg with nil, in which case we should not sleep.
+	return atomic.CompareAndSwapPointer(wg, (unsafe.Pointer)(&preparingG), g)
+}