Work around sigaltstack() bug on Mac OS X when unregistering a signal stack

src/native_client/src/trusted/service_runtime/posix/nacl_signal.c

 /*
  * Copyright 2010 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 <errno.h>
 #include <signal.h>
 #include <string.h>
 #include <sys/mman.h>
@@ skipping 128 matching lines @@
 }
 
 void NaClSignalStackUnregister(void) {
   /*
    * Unregister the signal stack in case a fault occurs between the
    * thread deallocating the signal stack and exiting.  Such a fault
    * could be unsafe if the address space were reallocated before the
    * fault, although that is unlikely.
    */
   stack_t st;
+#if NACL_OSX
+  /*
+   * This is a workaround for a bug in Mac OS X's libc, in which new
+   * versions of the sigaltstack() wrapper return ENOMEM if ss_size is
+   * less than MINSIGSTKSZ, even when ss_size should be ignored
+   * because we are unregistering the signal stack.
+   * See http://code.google.com/p/nativeclient/issues/detail?id=1053
+   */
+  st.ss_size = MINSIGSTKSZ;
+#else
   st.ss_size = 0;
+#endif
   st.ss_sp = NULL;
   st.ss_flags = SS_DISABLE;
   if (sigaltstack(&st, NULL) != 0) {
     NaClLog(LOG_FATAL, "Failed to unregister signal stack\n");
   }
 }
 
 
 static void ExceptionCatch(int sig, siginfo_t *info, void *uc) {
   int untrusted = 0;
@@ skipping 85 matching lines @@
   int a;
 
   /* Remove all handlers */
   for (a = 0; a < SIGNAL_COUNT; a++) {
     if (sigaction(s_Signals[a], &s_OldActions[a], NULL) != 0) {
       NaClLog(LOG_FATAL, "Failed to unregister handler for %d.\n\tERR:%s\n",
                           s_Signals[a], strerror(errno));
     }
   }
 }