Avoid setting an alternative stack for signals if there is already one

P=Mike Hommey <mh@glandium.org>
R=ted at http://codereview.appspot.com/5573054/

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@918 4c0a9323-5329-0410-9bdc-e9ce6186880e

2 files changed, 11 insertions, 8 deletions

diff --git a/src/client/linux/handler/exception_handler.cc b/src/client/linux/handler/exception_handler.cc
index 823823d4..fff2d1c6 100644
--- a/src/client/linux/handler/exception_handler.cc
+++ b/src/client/linux/handler/exception_handler.cc
@@ -187,14 +187,18 @@ bool ExceptionHandler::InstallHandlers() {
   // such a small stack.
   static const unsigned kSigStackSize = 8192;
 
-  signal_stack = malloc(kSigStackSize);
   stack_t stack;
-  memset(&stack, 0, sizeof(stack));
-  stack.ss_sp = signal_stack;
-  stack.ss_size = kSigStackSize;
-
-  if (sys_sigaltstack(&stack, NULL) == -1)
-    return false;
+  // 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 = malloc(kSigStackSize);
+    stack.ss_size = kSigStackSize;
+
+    if (sys_sigaltstack(&stack, NULL) == -1)
+      return false;
+  }
 
   struct sigaction sa;
   memset(&sa, 0, sizeof(sa));
diff --git a/src/client/linux/handler/exception_handler.h b/src/client/linux/handler/exception_handler.h
index e75517ea..94766eba 100644
--- a/src/client/linux/handler/exception_handler.h
+++ b/src/client/linux/handler/exception_handler.h
@@ -228,7 +228,6 @@ 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