Mac: Enable Mach exception handler by default

src/trusted/service_runtime/sel_main.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.
  */
 
 /*
  * NaCl Simple/secure ELF loader (NaCl SEL).
  */
 #include "native_client/src/include/portability.h"
@@ skipping 467 matching lines @@
   if (getenv("NACL_UNTRUSTED_EXCEPTION_HANDLING") != NULL) {
     state.enable_exception_handling = 1;
   }
   if (state.enable_exception_handling || enable_debug_stub) {
 #if NACL_WINDOWS
     state.attach_debug_exception_handler_func =
         NaClDebugExceptionHandlerStandaloneAttach;
 #elif NACL_LINUX
     /* NaCl's signal handler is always enabled on Linux. */
 #elif NACL_OSX
-    if (!NaClInterceptMachExceptions()) {
-      fprintf(stderr, "ERROR setting up Mach exception interception.\n");
-      return -1;
-    }
 #else
 # error Unknown host OS
 #endif
   }
   if (NACL_LINUX) {
     handle_signals = 1;
   }
+#if NACL_OSX
+  if (!NaClInterceptMachExceptions()) {
+    fprintf(stderr, "ERROR setting up Mach exception interception.\n");
+    return -1;
+  }
+#endif
 
   errcode = LOAD_OK;
 
   /*
    * in order to report load error to the browser plugin through the
    * secure command channel, we do not immediate jump to cleanup code
    * on error.  rather, we continue processing (assuming earlier
    * errors do not make it inappropriate) until the secure command
    * channel is set up, and then bail out.
    */
@@ skipping 18 matching lines @@
       errcode = pq_error;
       nap->module_load_status = pq_error;
       fprintf(stderr, "Error while loading \"%s\": %s\n",
               NULL != nacl_file ? nacl_file
                                 : "(no file, to-be-supplied-via-RPC)",
               NaClErrorString(errcode));
     }
   }
 
   if (handle_signals) {
+#if NACL_LINUX
     NaClSignalHandlerInit();
+#endif
   } else {
     /*
      * Patch the Windows exception dispatcher to be safe in the case
      * of faults inside x86-64 sandboxed code.  The sandbox is not
      * secure on 64-bit Windows without this.
      */
 #if (NACL_WINDOWS && NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86 && \
      NACL_BUILD_SUBARCH == 64)
     NaClPatchWindowsExceptionDispatcher();
 #endif
@@ skipping 311 matching lines @@
   fflush(stdout);
 
   if (handle_signals) NaClSignalHandlerFini();
   NaClAllModulesFini();
 
   NaClExit(ret_code);
 
   /* Unreachable, but having the return prevents a compiler error. */
   return ret_code;
 }