Revert "Disable exit-on-SIGPIPE in lldb"

This reverts commit 32ce14e55e.

In post-commit review, Pavel pointed out that there's a simpler way to
ignore SIGPIPE in lldb that doesn't rely on llvm's handlers.

lldb/tools/driver/Driver.cpp

@@ -853,16 +853,6 @@ int main(int argc, char const *argv[])
   signal(SIGCONT, sigcont_handler);
 #endif
 
-  // 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. However, LLVM's default SIGPIPE behavior
-  // is to exit with IO_ERR. Opt LLDB out of that.
-  //
-  // We don't disable LLVM's signal handling entirely because we still want
-  // pretty stack traces, and file cleanup (for when, say, the clang embedded
-  // in LLDB leaves behind temporary objects).
-  llvm::sys::SetPipeSignalFunction(nullptr);
-
   int exit_code = 0;
   // Create a scope for driver so that the driver object will destroy itself
   // before SBDebugger::Terminate() is called.

llvm/include/llvm/Support/Signals.h

@@ -84,17 +84,6 @@ namespace sys {
   /// function.  Note also that the handler may be executed on a different
   /// thread on some platforms.
   void SetInfoSignalFunction(void (*Handler)());
-
-  /// Registers a function to be called when a "pipe" signal is delivered to
-  /// the process.
-  ///
-  /// The "pipe" signal typically indicates a failed write to a pipe (SIGPIPE).
-  /// The default installed handler calls `exit(EX_IOERR)`, causing the process
-  /// to immediately exit with an IO error exit code.
-  ///
-  /// This function is only applicable on POSIX systems.
-  void SetPipeSignalFunction(void (*Handler)());
-
 } // End sys namespace
 } // End llvm namespace
 

llvm/lib/Support/Unix/Signals.inc

@@ -82,18 +82,12 @@ using namespace llvm;
 static RETSIGTYPE SignalHandler(int Sig);  // defined below.
 static RETSIGTYPE InfoSignalHandler(int Sig);  // defined below.
 
-static void DefaultPipeSignalFunction() {
-  exit(EX_IOERR);
-}
-
 using SignalHandlerFunctionType = void (*)();
 /// The function to call if ctrl-c is pressed.
 static std::atomic<SignalHandlerFunctionType> InterruptFunction =
     ATOMIC_VAR_INIT(nullptr);
 static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =
     ATOMIC_VAR_INIT(nullptr);
-static std::atomic<SignalHandlerFunctionType> PipeSignalFunction =
-    ATOMIC_VAR_INIT(DefaultPipeSignalFunction);
 
 namespace {
 /// Signal-safe removal of files.
@@ -369,8 +363,7 @@ static RETSIGTYPE SignalHandler(int Sig) {
 
       // Send a special return code that drivers can check for, from sysexits.h.
       if (Sig == SIGPIPE)
-        if (SignalHandlerFunctionType CurrentPipeFunction = PipeSignalFunction)
+        exit(EX_IOERR);
-          CurrentPipeFunction();
 
       raise(Sig);   // Execute the default handler.
       return;
@@ -410,11 +403,6 @@ void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
   RegisterHandlers();
 }
 
-void llvm::sys::SetPipeSignalFunction(void (*Handler)()) {
-  PipeSignalFunction.exchange(Handler);
-  RegisterHandlers();
-}
-
 // The public API
 bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
                                    std::string* ErrMsg) {

llvm/lib/Support/Windows/Signals.inc

@@ -560,9 +560,6 @@ void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
   // Unimplemented.
 }
 
-void llvm::sys::SetPipeSignalFunction(void (*Handler)()) {
-  // Unimplemented.
-}
 
 /// Add a function to be called when a signal is delivered to the process. The
 /// handler can have a cookie passed to it to identify what instance of the

llvm/unittests/Support/CMakeLists.txt

@@ -58,7 +58,6 @@ add_llvm_unittest(SupportTests
   ReverseIterationTest.cpp
   ReplaceFileTest.cpp
   ScaledNumberTest.cpp
-  SignalsTest.cpp
   SourceMgrTest.cpp
   SpecialCaseListTest.cpp
   StringPool.cpp

llvm/unittests/Support/SignalsTest.cpp

@@ -1,54 +0,0 @@
-//========- 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>
-#include <signal.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)