Add wrapper library for the nacl_irt_exception_handling IRT interface

src/untrusted/nacl/nacl_exception.c

Index: src/untrusted/nacl/nacl_exception.c
diff --git a/src/untrusted/nacl/nacl_exception.c b/src/untrusted/nacl/nacl_exception.c
new file mode 100644
index 0000000000000000000000000000000000000000..2d80bd875eb9e114745090a282d9c74fa22be803
--- /dev/null
+++ b/src/untrusted/nacl/nacl_exception.c
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2013 The Native Client 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 "native_client/src/include/nacl/nacl_exception.h"
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include "native_client/src/untrusted/irt/irt.h"
+
+
+static struct nacl_irt_exception_handling irt_exception_handling;
+
+/*
+ * We don't do any locking here, but simultaneous calls are harmless enough.
+ * They'll all be writing the same values to the same words.
+ */
+static int set_up_irt_exception_handling(void) {
+  return nacl_interface_query(NACL_IRT_EXCEPTION_HANDLING_v0_1,
+                              &irt_exception_handling,
+                              sizeof(irt_exception_handling))
+         == sizeof(irt_exception_handling);
+}
+
+int nacl_exception_set_handler(nacl_exception_handler_t handler) {
+  if (irt_exception_handling.exception_handler == NULL) {
+    if (!set_up_irt_exception_handling())
+      return ENOSYS;
+  }
+  return irt_exception_handling.exception_handler(handler, NULL);
+}
+
+int nacl_exception_set_stack(void *stack, size_t size) {
+  if (irt_exception_handling.exception_stack == NULL) {
+    if (!set_up_irt_exception_handling())
+      return ENOSYS;
+  }
+  return irt_exception_handling.exception_stack(stack, size);
+}
+
+int nacl_exception_clear_flag() {
+  if (irt_exception_handling.exception_clear_flag == NULL) {
+    if (!set_up_irt_exception_handling())
+      return ENOSYS;
+  }
+  return irt_exception_handling.exception_clear_flag();
+}