crash_dump: clear the default crash handlers.

crash_dump is a dynamic executable that gets the default crash dumping
handlers set by the linker. Turn them off to prevent crash_dump from
dumping itself.

Bug: http://b/34472671
Test: inserted an abort into crash_dump
Change-Id: Ic9d708805ad47afbb2a9ff37e2ca059f23f421de

debuggerd/crash_dump.cpp

@@ -160,6 +160,12 @@ static bool tombstoned_notify_completion(int tombstoned_socket) {
   return true;
 }
 
+static void signal_handler(int) {
+  // We can't log easily, because the heap might be corrupt.
+  // Just die and let the surrounding log context explain things.
+  _exit(1);
+}
+
 static void abort_handler(pid_t target, const bool& tombstoned_connected,
                           unique_fd& tombstoned_socket, unique_fd& output_fd,
                           const char* abort_msg) {
@@ -175,7 +181,6 @@ static void abort_handler(pid_t target, const bool& tombstoned_connected,
 
   dprintf(output_fd.get(), "crash_dump failed to dump process %d: %s\n", target, abort_msg);
 
-  // Don't dump ourselves.
   _exit(1);
 }
 
@@ -201,6 +206,11 @@ int main(int argc, char** argv) {
     abort_handler(target, tombstoned_connected, tombstoned_socket, output_fd, abort_msg);
   });
 
+  // Don't try to dump ourselves.
+  struct sigaction action = {};
+  action.sa_handler = signal_handler;
+  debuggerd_register_handlers(&action);
+
   if (argc != 2) {
     return 1;
   }

debuggerd/handler/debuggerd_handler.cpp

@@ -367,15 +367,5 @@ void debuggerd_init(debuggerd_callbacks_t* callbacks) {
 
   // Use the alternate signal stack if available so we can catch stack overflows.
   action.sa_flags |= SA_ONSTACK;
-
-  sigaction(SIGABRT, &action, nullptr);
-  sigaction(SIGBUS, &action, nullptr);
-  sigaction(SIGFPE, &action, nullptr);
-  sigaction(SIGILL, &action, nullptr);
-  sigaction(SIGSEGV, &action, nullptr);
-#if defined(SIGSTKFLT)
-  sigaction(SIGSTKFLT, &action, nullptr);
-#endif
-  sigaction(SIGTRAP, &action, nullptr);
-  sigaction(DEBUGGER_SIGNAL, &action, nullptr);
+  debuggerd_register_handlers(&action);
 }

debuggerd/include/debuggerd/handler.h

@@ -39,4 +39,17 @@ void debuggerd_init(debuggerd_callbacks_t* callbacks);
 // to the log.
 #define DEBUGGER_SIGNAL (__SIGRTMIN + 3)
 
+static void __attribute__((__unused__)) debuggerd_register_handlers(struct sigaction* action) {
+  sigaction(SIGABRT, action, nullptr);
+  sigaction(SIGBUS, action, nullptr);
+  sigaction(SIGFPE, action, nullptr);
+  sigaction(SIGILL, action, nullptr);
+  sigaction(SIGSEGV, action, nullptr);
+#if defined(SIGSTKFLT)
+  sigaction(SIGSTKFLT, action, nullptr);
+#endif
+  sigaction(SIGTRAP, action, nullptr);
+  sigaction(DEBUGGER_SIGNAL, action, nullptr);
+}
+
 __END_DECLS