1 files changed, 43 insertions, 0 deletions
diff --git a/include/accel/tcg/helper-retaddr.h b/include/accel/tcg/helper-retaddr.h
new file mode 100644
index 0000000..037fda2
--- /dev/null
+++ b/include/accel/tcg/helper-retaddr.h
@@ -0,0 +1,43 @@
+/*
+ * Get user helper pc for memory unwinding.
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#ifndef ACCEL_TCG_HELPER_RETADDR_H
+#define ACCEL_TCG_HELPER_RETADDR_H
+
+/*
+ * For user-only, helpers that use guest to host address translation
+ * must protect the actual host memory access by recording 'retaddr'
+ * for the signal handler.  This is required for a race condition in
+ * which another thread unmaps the page between a probe and the
+ * actual access.
+ */
+#ifdef CONFIG_USER_ONLY
+extern __thread uintptr_t helper_retaddr;
+
+static inline void set_helper_retaddr(uintptr_t ra)
+{
+    helper_retaddr = ra;
+    /*
+     * Ensure that this write is visible to the SIGSEGV handler that
+     * may be invoked due to a subsequent invalid memory operation.
+     */
+    signal_barrier();
+}
+
+static inline void clear_helper_retaddr(void)
+{
+    /*
+     * Ensure that previous memory operations have succeeded before
+     * removing the data visible to the signal handler.
+     */
+    signal_barrier();
+    helper_retaddr = 0;
+}
+#else
+#define set_helper_retaddr(ra)   do { } while (0)
+#define clear_helper_retaddr()   do { } while (0)
+#endif
+
+#endif /* ACCEL_TCG_HELPER_RETADDR_H */