Bug 720704 - Avoid setting an alternative stack for signals if there is already one. r=ted

toolkit/crashreporter/google-breakpad/src/client/linux/handler/exception_handler.cc

@@ -190,14 +190,18 @@ bool ExceptionHandler::InstallHandlers() {
   // such a small stack.
   static const unsigned kSigStackSize = 8192;
 
-  signal_stack = malloc(kSigStackSize);
   stack_t stack;
+  // Only set an alternative stack if there isn't already one, or if the current
+  // one is too small.
+  if (sys_sigaltstack(NULL, &stack) == -1 || !stack.ss_sp ||
+      stack.ss_size < kSigStackSize) {
     memset(&stack, 0, sizeof(stack));
-  stack.ss_sp = signal_stack;
+    stack.ss_sp = malloc(kSigStackSize);
     stack.ss_size = kSigStackSize;
 
     if (sys_sigaltstack(&stack, NULL) == -1)
       return false;
+  }
 
   struct sigaction sa;
   memset(&sa, 0, sizeof(sa));

toolkit/crashreporter/google-breakpad/src/client/linux/handler/exception_handler.h

@@ -259,7 +259,6 @@ class ExceptionHandler {
   const char* next_minidump_id_c_;
 
   const bool handler_installed_;
-  void* signal_stack;  // the handler stack.
   HandlerCallback crash_handler_;
 
   // The global exception handler stack. This is need becuase there may exist