Merge commit '48f68ac91784' from apple/stable/20190619 into swift/master

Author: git apple-llvm automerger

lldb/tools/driver/Driver.cpp

@@ -858,6 +858,25 @@ main(int argc, char const *argv[])
   }
   SBHostOS::ThreadCreated("<lldb.driver.main-thread>");
 
+  // Install llvm's signal handlers up front to prevent lldb's handlers from
+  // being ignored. This is (hopefully) a stopgap workaround.
+  //
+  // When lldb invokes an llvm API that installs signal handlers (e.g.
+  // llvm::sys::RemoveFileOnSignal, possibly via a compiler embedded within
+  // lldb), lldb's signal handlers are overriden if llvm is installing its
+  // handlers for the first time.
+  //
+  // To work around llvm's behavior, force it to install its handlers up front,
+  // and *then* install lldb's handlers. In practice this is used to prevent
+  // lldb test processes from exiting due to IO_ERR when SIGPIPE is received.
+  //
+  // Note that when llvm installs its handlers, it 1) records the old handlers
+  // it replaces and 2) re-installs the old handlers when its new handler is
+  // invoked. That means that a signal not explicitly handled by lldb can fall
+  // back to being handled by llvm's handler the first time it is received,
+  // and then by the default handler the second time it is received.
+  llvm::sys::AddSignalHandler([](void *) -> void {}, nullptr);
+
   signal(SIGINT, sigint_handler);
 #if !defined(_MSC_VER)
   signal(SIGPIPE, SIG_IGN);