diff -r 000000000000 -r 6474c204b198 toolkit/xre/MacLaunchHelper.mm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/xre/MacLaunchHelper.mm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,90 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MacLaunchHelper.h"
+
+#include "nsMemory.h"
+#include "nsAutoPtr.h"
+#include "nsIAppStartup.h"
+
+#include <stdio.h>
+#include <spawn.h>
+#include <crt_externs.h>
+
+using namespace mozilla;
+
+namespace {
+cpu_type_t pref_cpu_types[2] = {
+#if defined(__i386__)
+                                 CPU_TYPE_X86,
+#elif defined(__x86_64__)
+                                 CPU_TYPE_X86_64,
+#elif defined(__ppc__)
+                                 CPU_TYPE_POWERPC,
+#endif
+                                 CPU_TYPE_ANY };
+
+cpu_type_t cpu_i386_types[2] = {
+                                 CPU_TYPE_X86,
+                                 CPU_TYPE_ANY };
+
+cpu_type_t cpu_x64_86_types[2] = {
+                                 CPU_TYPE_X86_64,
+                                 CPU_TYPE_ANY };
+}
+
+void LaunchChildMac(int aArgc, char** aArgv,
+                    uint32_t aRestartType, pid_t *pid)
+{
+  // "posix_spawnp" uses null termination for arguments rather than a count.
+  // Note that we are not duplicating the argument strings themselves.
+  nsAutoArrayPtr<char*> argv_copy(new char*[aArgc + 1]);
+  for (int i = 0; i < aArgc; i++) {
+    argv_copy[i] = aArgv[i];
+  }
+  argv_copy[aArgc] = NULL;
+
+  // Initialize spawn attributes.
+  posix_spawnattr_t spawnattr;
+  if (posix_spawnattr_init(&spawnattr) != 0) {
+    printf("Failed to init posix spawn attribute.");
+    return;
+  }
+
+  cpu_type_t *wanted_type = pref_cpu_types;
+  size_t attr_count = ArrayLength(pref_cpu_types);
+
+  if (aRestartType & nsIAppStartup::eRestarti386) {
+    wanted_type = cpu_i386_types;
+    attr_count = ArrayLength(cpu_i386_types);
+  } else if (aRestartType & nsIAppStartup::eRestartx86_64) {
+    wanted_type = cpu_x64_86_types;
+    attr_count = ArrayLength(cpu_x64_86_types);
+  }
+
+  // Set spawn attributes.
+  size_t attr_ocount = 0;
+  if (posix_spawnattr_setbinpref_np(&spawnattr, attr_count, wanted_type, &attr_ocount) != 0 ||
+      attr_ocount != attr_count) {
+    printf("Failed to set binary preference on posix spawn attribute.");
+    posix_spawnattr_destroy(&spawnattr);
+    return;
+  }
+
+  // Pass along our environment.
+  char** envp = NULL;
+  char*** cocoaEnvironment = _NSGetEnviron();
+  if (cocoaEnvironment) {
+    envp = *cocoaEnvironment;
+  }
+
+  int result = posix_spawnp(pid, argv_copy[0], NULL, &spawnattr, argv_copy, envp);
+
+  posix_spawnattr_destroy(&spawnattr);
+
+  if (result != 0) {
+    printf("Process spawn failed with code %d!", result);
+  }
+}