Merge 1447 "Fix call to rt_sigaction"

> Fix call to rt_sigaction
> 
> Despite the fact that many places imply that sigaction and rt_sigaction
> are essentially the same, rt_sigaction's signature is actually
> different-- it takes the size of the kernel's sigset_t as an extra argument.
> 
> BUG=473973
> 

TBR=cjhopman@chromium.org

Review URL: https://breakpad.appspot.com/5784002

git-svn-id: http://google-breakpad.googlecode.com/svn/branches/chrome_42@1448 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/client/linux/handler/exception_handler.cc

@@ -188,6 +188,24 @@ void RestoreAlternateStackLocked() {
   stack_installed = false;
 }
 
+void InstallDefaultHandler(int sig) {
+#if defined(__ANDROID__)
+  // Android L+ expose signal and sigaction symbols that override the system
+  // ones. There is a bug in these functions where a request to set the handler
+  // to SIG_DFL is ignored. In that case, an infinite loop is entered as the
+  // signal is repeatedly sent to breakpad's signal handler.
+  // To work around this, directly call the system's sigaction.
+  struct kernel_sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  sys_sigemptyset(&sa.sa_mask);
+  sa.sa_handler_ = SIG_DFL;
+  sa.sa_flags = SA_RESTART;
+  sys_rt_sigaction(sig, &sa, NULL, sizeof(kernel_sigset_t));
+#else
+  signal(sig, SIG_DFL);
+#endif
+}
+
 // The global exception handler stack. This is needed because there may exist
 // multiple ExceptionHandler instances in a process. Each will have itself
 // registered in this stack.
@@ -283,7 +301,7 @@ void ExceptionHandler::RestoreHandlersLocked() {
 
   for (int i = 0; i < kNumHandledSignals; ++i) {
     if (sigaction(kExceptionSignals[i], &old_handlers[i], NULL) == -1) {
-      signal(kExceptionSignals[i], SIG_DFL);
+      InstallDefaultHandler(kExceptionSignals[i]);
     }
   }
   handlers_installed = false;
@@ -323,7 +341,7 @@ void ExceptionHandler::SignalHandler(int sig, siginfo_t* info, void* uc) {
     if (sigaction(sig, &cur_handler, NULL) == -1) {
       // When resetting the handler fails, try to reset the
       // default one to avoid an infinite loop here.
-      signal(sig, SIG_DFL);
+      InstallDefaultHandler(sig);
     }
     pthread_mutex_unlock(&g_handler_stack_mutex_);
     return;
@@ -340,7 +358,7 @@ void ExceptionHandler::SignalHandler(int sig, siginfo_t* info, void* uc) {
   // previously installed handler. Then, when the signal is retriggered, it will
   // be delivered to the appropriate handler.
   if (handled) {
-    signal(sig, SIG_DFL);
+    InstallDefaultHandler(sig);
   } else {
     RestoreHandlersLocked();
   }