1 files changed, 69 insertions, 0 deletions
diff --git a/libgo/runtime/go-recover.c b/libgo/runtime/go-recover.c
new file mode 100644
index 0000000000..4de122e3b3
--- /dev/null
+++ b/libgo/runtime/go-recover.c
@@ -0,0 +1,69 @@
+/* go-recover.c -- support for the go recover function.
+
+   Copyright 2010 The Go Authors. All rights reserved.
+   Use of this source code is governed by a BSD-style
+   license that can be found in the LICENSE file.  */
+
+#include "interface.h"
+#include "go-panic.h"
+#include "go-defer.h"
+
+/* This is called by a thunk to see if the real function should be
+   permitted to recover a panic value.  Recovering a value is
+   permitted if the thunk was called directly by defer.  RETADDR is
+   the return address of the function which is calling
+   __go_can_recover--this is, the thunk.  */
+
+_Bool
+__go_can_recover (const void* retaddr)
+{
+  struct __go_defer_stack *d;
+  const char* ret;
+  const char* dret;
+
+  if (__go_panic_defer == NULL)
+    return 0;
+  d = __go_panic_defer->__defer;
+  if (d == NULL)
+    return 0;
+
+  /* The panic which this function would recover is the one on the top
+     of the panic stack.  We do not want to recover it if that panic
+     was on the top of the panic stack when this function was
+     deferred.  */
+  if (d->__panic == __go_panic_defer->__panic)
+    return 0;
+
+  /* D->__RETADDR is the address of a label immediately following the
+     call to the thunk.  We can recover a panic if that is the same as
+     the return address of the thunk.  We permit a bit of slack in
+     case there is any code between the function return and the label,
+     such as an instruction to adjust the stack pointer.  */
+
+  ret = (const char *) retaddr;
+  dret = (const char *) d->__retaddr;
+  return ret <= dret && ret + 16 >= dret;
+}
+
+/* This is only called when it is valid for the caller to recover the
+   value on top of the panic stack, if there is one.  */
+
+struct __go_empty_interface
+__go_recover ()
+{
+  struct __go_panic_stack *p;
+
+  if (__go_panic_defer == NULL
+      || __go_panic_defer->__panic == NULL
+      || __go_panic_defer->__panic->__was_recovered)
+    {
+      struct __go_empty_interface ret;
+
+      ret.__type_descriptor = NULL;
+      ret.__object = NULL;
+      return ret;
+    }
+  p = __go_panic_defer->__panic;
+  p->__was_recovered = 1;
+  return p->__arg;
+}