Mac: Enable Mach exception handler by default

src/trusted/service_runtime/osx/mach_exception_handler.c

 /*
  * Copyright (c) 2012 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/trusted/service_runtime/osx/mach_exception_handler.h"
 
 #include <mach/mach.h>
 #include <mach/mach_vm.h>
@@ skipping 26 matching lines @@
 
 /*
  * MIG generated message pump from /usr/include/mach/exc.defs
  * Tweaked to place in an isolated namespace.
  */
 boolean_t nacl_exc_server(
     mach_msg_header_t *InHeadP,
     mach_msg_header_t *OutHeadP);
 
 
-/* Exception types to intercept. */
+/* Exception types to intercept.  This should be a superset of what Breakpad handles... */
 #define NACL_MACH_EXCEPTION_MASK \
     (EXC_MASK_BAD_ACCESS | \
      EXC_MASK_BAD_INSTRUCTION | \
      EXC_MASK_ARITHMETIC | \
      EXC_MASK_BREAKPOINT)
 
 /*
  * <mach/mach_types.defs> says that the arrays in MachExceptionParameters have
  * room for 32 elements.  EXC_TYPES_COUNT, a smaller value, has grown over
  * time in major SDK releases.  task_get_exception_ports expects there to be
@@ skipping 341 matching lines @@
    * handlers don't provide a new thread state. They can set a new thread
    * state on their own by calling thread_set_state. Returning KERN_SUCCESS
    * would allow the old state passed to
    * nacl_catch_exception_raise_state_identity to overwrite any new state set
    * by the handler that the exception was forwarded to via exception_raise.
    */
   return kr == KERN_SUCCESS ? MACH_RCV_PORT_DIED : kr;
 }
 
 
+static void ReportCrash(int exception_type, int is_untrusted) {
+  char buf[128];
+  int len = snprintf(buf, sizeof(buf),
+                     "\n** Mach exception %d from %s code\n",
+                     exception_type,
+                     is_untrusted ? "untrusted" : "trusted");
+  write(2, buf, len);
+}
+
+
 kern_return_t nacl_catch_exception_raise(
     mach_port_t exception_port,
     mach_port_t thread,
     mach_port_t task,
     exception_type_t exception,
     exception_data_t code,
     mach_msg_type_number_t code_count) {
   /* MIG generated code expects this, but should never be called. */
   UNREFERENCED_PARAMETER(exception_port);
   UNREFERENCED_PARAMETER(thread);
@@ skipping 72 matching lines @@
      * xnu-2050.18.24/osfmk/kern/exception.c.
      *
      * This is done instead of letting the kernel set the new thread state to
      * be the same as the old state because the kernel resets %cs to the
      * default value when setting a thread's state. This behavior is explained
      * in more detail in HandleException.
      */
     return MACH_RCV_PORT_DIED;
   }
 
+  ReportCrash(exception, is_untrusted);
+
   /*
    * Don't forward if the crash is untrusted, but unhandled.
    * (As we don't want things like Breakpad handling the crash.)
    */
   if (is_untrusted) {
     return KERN_FAILURE;
   }
 
   /* Forward on the exception to the old set of ports. */
   return ForwardException(
@@ skipping 141 matching lines @@
   if (data) {
     if (MACH_PORT_NULL != data->exception_port) {
       mach_port_deallocate(current_task, data->exception_port);
     }
     free(data);
   }
   return FALSE;
 }
 
 #endif  /* NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86 */