Disable exit-on-SIGPIPE in lldb

Occasionally, during test teardown, LLDB writes to a closed pipe.
Sometimes the communication is inherently unreliable, so LLDB tries to
avoid being killed due to SIGPIPE (it calls `signal(SIGPIPE, SIG_IGN)`).
However, LLVM's default SIGPIPE behavior overrides LLDB's, causing it to
exit with IO_ERR.

Opt LLDB out of the default SIGPIPE behavior. I expect that this will
resolve some LLDB test suite flakiness (tests randomly failing with
IO_ERR) that we've seen since r344372.

rdar://55750240

Differential Revision: https://reviews.llvm.org/D69148

llvm-svn: 375288

2 files changed, 54 insertions, 0 deletions

diff --git a/llvm/unittests/Support/CMakeLists.txt b/llvm/unittests/Support/CMakeLists.txt
index 161891517cf..385142278e4 100644
--- a/llvm/unittests/Support/CMakeLists.txt
+++ b/llvm/unittests/Support/CMakeLists.txt
@@ -58,6 +58,7 @@ add_llvm_unittest(SupportTests
   ReverseIterationTest.cpp
   ReplaceFileTest.cpp
   ScaledNumberTest.cpp
+  SignalsTest.cpp
   SourceMgrTest.cpp
   SpecialCaseListTest.cpp
   StringPool.cpp
diff --git a/llvm/unittests/Support/SignalsTest.cpp b/llvm/unittests/Support/SignalsTest.cpp
new file mode 100644
index 00000000000..6dfa4bf996d
--- /dev/null
+++ b/llvm/unittests/Support/SignalsTest.cpp
@@ -0,0 +1,53 @@
+//========- unittests/Support/SignalsTest.cpp - Signal handling test =========//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#if !defined(_WIN32)
+#include <unistd.h>
+#include <sysexits.h>
+#endif // !defined(_WIN32)
+
+#include "llvm/Support/Signals.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+#if !defined(_WIN32)
+TEST(SignalTest, IgnoreMultipleSIGPIPEs) {
+  // Ignore SIGPIPE.
+  signal(SIGPIPE, SIG_IGN);
+
+  // Disable exit-on-SIGPIPE.
+  sys::SetPipeSignalFunction(nullptr);
+
+  // Create unidirectional read/write pipes.
+  int fds[2];
+  int err = pipe(fds);
+  if (err != 0)
+    return; // If we can't make pipes, this isn't testing anything.
+
+  // Close the read pipe.
+  close(fds[0]);
+
+  // Attempt to write to the write pipe. Currently we're asserting that the
+  // write fails, which isn't great.
+  //
+  // What we really want is a death test that checks that this block exits
+  // with a special exit "success" code, as opposed to unexpectedly exiting due
+  // to a kill-by-SIGNAL or due to the default SIGPIPE handler.
+  //
+  // Unfortunately llvm's unit tests aren't set up to support death tests well.
+  // For one, death tests are flaky in a multithreaded context. And sigactions
+  // inherited from llvm-lit interfere with what's being tested.
+  const void *buf = (const void *)&fds;
+  err = write(fds[1], buf, 1);
+  ASSERT_EQ(err, -1);
+  err = write(fds[1], buf, 1);
+  ASSERT_EQ(err, -1);
+}
+#endif // !defined(_WIN32)