[lldb] Use Socket::CreatePair for launching debugserver (#145017)

This lets get rid of platform-specific code in ProcessGDBRemote and use
the
same code path (module differences in socket types) everywhere. It also
unlocks
further cleanups in the debugserver launching code.

The main effect of this change is that lldb on windows will now use the
`--fd` lldb-server argument for "local remote" debug sessions instead of
having lldb-server connect back to lldb. This is the same method used by
lldb on non-windows platforms (for many years) and "lldb-server
platform" on windows for truly remote debug sessions (for ~one year).

Depends on #145015.

Author: labath

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

@@ -3447,115 +3447,80 @@ ProcessGDBRemote::EstablishConnectionIfNeeded(const ProcessInfo &process_info) {
   }
   return error;
 }
-#if !defined(_WIN32)
-#define USE_SOCKETPAIR_FOR_LOCAL_CONNECTION 1
-#endif
-
-#ifdef USE_SOCKETPAIR_FOR_LOCAL_CONNECTION
-static bool SetCloexecFlag(int fd) {
-#if defined(FD_CLOEXEC)
-  int flags = ::fcntl(fd, F_GETFD);
-  if (flags == -1)
-    return false;
-  return (::fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == 0);
-#else
-  return false;
-#endif
-}
-#endif
 
 Status ProcessGDBRemote::LaunchAndConnectToDebugserver(
     const ProcessInfo &process_info) {
   using namespace std::placeholders; // For _1, _2, etc.
 
-  Status error;
-  if (m_debugserver_pid == LLDB_INVALID_PROCESS_ID) {
-    // If we locate debugserver, keep that located version around
-    static FileSpec g_debugserver_file_spec;
+  if (m_debugserver_pid != LLDB_INVALID_PROCESS_ID)
+    return Status();
 
-    ProcessLaunchInfo debugserver_launch_info;
-    // Make debugserver run in its own session so signals generated by special
-    // terminal key sequences (^C) don't affect debugserver.
-    debugserver_launch_info.SetLaunchInSeparateProcessGroup(true);
+  ProcessLaunchInfo debugserver_launch_info;
+  // Make debugserver run in its own session so signals generated by special
+  // terminal key sequences (^C) don't affect debugserver.
+  debugserver_launch_info.SetLaunchInSeparateProcessGroup(true);
 
-    const std::weak_ptr<ProcessGDBRemote> this_wp =
-        std::static_pointer_cast<ProcessGDBRemote>(shared_from_this());
-    debugserver_launch_info.SetMonitorProcessCallback(
-        std::bind(MonitorDebugserverProcess, this_wp, _1, _2, _3));
-    debugserver_launch_info.SetUserID(process_info.GetUserID());
+  const std::weak_ptr<ProcessGDBRemote> this_wp =
+      std::static_pointer_cast<ProcessGDBRemote>(shared_from_this());
+  debugserver_launch_info.SetMonitorProcessCallback(
+      std::bind(MonitorDebugserverProcess, this_wp, _1, _2, _3));
+  debugserver_launch_info.SetUserID(process_info.GetUserID());
 
 #if defined(__APPLE__)
-    // On macOS 11, we need to support x86_64 applications translated to
-    // arm64. We check whether a binary is translated and spawn the correct
-    // debugserver accordingly.
-    int mib[] = { CTL_KERN, KERN_PROC, KERN_PROC_PID,
-                  static_cast<int>(process_info.GetProcessID()) };
-    struct kinfo_proc processInfo;
-    size_t bufsize = sizeof(processInfo);
-    if (sysctl(mib, (unsigned)(sizeof(mib)/sizeof(int)), &processInfo,
-               &bufsize, NULL, 0) == 0 && bufsize > 0) {
-      if (processInfo.kp_proc.p_flag & P_TRANSLATED) {
-        FileSpec rosetta_debugserver("/Library/Apple/usr/libexec/oah/debugserver");
-        debugserver_launch_info.SetExecutableFile(rosetta_debugserver, false);
-      }
+  // On macOS 11, we need to support x86_64 applications translated to
+  // arm64. We check whether a binary is translated and spawn the correct
+  // debugserver accordingly.
+  int mib[] = {CTL_KERN, KERN_PROC, KERN_PROC_PID,
+               static_cast<int>(process_info.GetProcessID())};
+  struct kinfo_proc processInfo;
+  size_t bufsize = sizeof(processInfo);
+  if (sysctl(mib, (unsigned)(sizeof(mib) / sizeof(int)), &processInfo, &bufsize,
+             NULL, 0) == 0 &&
+      bufsize > 0) {
+    if (processInfo.kp_proc.p_flag & P_TRANSLATED) {
+      FileSpec rosetta_debugserver(
+          "/Library/Apple/usr/libexec/oah/debugserver");
+      debugserver_launch_info.SetExecutableFile(rosetta_debugserver, false);
     }
+  }
 #endif
 
-    shared_fd_t communication_fd = SharedSocket::kInvalidFD;
-#ifdef USE_SOCKETPAIR_FOR_LOCAL_CONNECTION
-    // Use a socketpair on non-Windows systems for security and performance
-    // reasons.
-    int sockets[2]; /* the pair of socket descriptors */
-    if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) == -1) {
-      error = Status::FromErrno();
-      return error;
-    }
+  llvm::Expected<Socket::Pair> socket_pair = Socket::CreatePair();
+  if (!socket_pair)
+    return Status::FromError(socket_pair.takeError());
 
-    int our_socket = sockets[0];
-    int gdb_socket = sockets[1];
-    auto cleanup_our = llvm::make_scope_exit([&]() { close(our_socket); });
-    auto cleanup_gdb = llvm::make_scope_exit([&]() { close(gdb_socket); });
+  Status error;
+  SharedSocket shared_socket(socket_pair->first.get(), error);
+  if (error.Fail())
+    return error;
 
-    // Don't let any child processes inherit our communication socket
-    SetCloexecFlag(our_socket);
-    communication_fd = gdb_socket;
-#endif
+  error = m_gdb_comm.StartDebugserverProcess(
+      nullptr, GetTarget().GetPlatform().get(), debugserver_launch_info,
+      nullptr, nullptr, shared_socket.GetSendableFD());
 
-    error = m_gdb_comm.StartDebugserverProcess(
-        nullptr, GetTarget().GetPlatform().get(), debugserver_launch_info,
-        nullptr, nullptr, communication_fd);
+  if (error.Fail()) {
+    Log *log = GetLog(GDBRLog::Process);
 
-    if (error.Success())
-      m_debugserver_pid = debugserver_launch_info.GetProcessID();
-    else
-      m_debugserver_pid = LLDB_INVALID_PROCESS_ID;
-
-    if (m_debugserver_pid != LLDB_INVALID_PROCESS_ID) {
-#ifdef USE_SOCKETPAIR_FOR_LOCAL_CONNECTION
-      // Our process spawned correctly, we can now set our connection to use
-      // our end of the socket pair
-      cleanup_our.release();
-      m_gdb_comm.SetConnection(
-          std::make_unique<ConnectionFileDescriptor>(our_socket, true));
-#endif
-      StartAsyncThread();
-    }
+    LLDB_LOGF(log, "failed to start debugserver process: %s",
+              error.AsCString());
+    return error;
+  }
 
-    if (error.Fail()) {
-      Log *log = GetLog(GDBRLog::Process);
+  m_debugserver_pid = debugserver_launch_info.GetProcessID();
+  shared_socket.CompleteSending(m_debugserver_pid);
 
-      LLDB_LOGF(log, "failed to start debugserver process: %s",
-                error.AsCString());
-      return error;
-    }
+  // Our process spawned correctly, we can now set our connection to use
+  // our end of the socket pair
+  m_gdb_comm.SetConnection(std::make_unique<ConnectionFileDescriptor>(
+      socket_pair->second.release()));
+  StartAsyncThread();
 
-    if (m_gdb_comm.IsConnected()) {
-      // Finish the connection process by doing the handshake without
-      // connecting (send NULL URL)
-      error = ConnectToDebugserver("");
-    } else {
-      error = Status::FromErrorString("connection failed");
-    }
+  if (m_gdb_comm.IsConnected()) {
+    // Finish the connection process by doing the handshake without
+    // connecting (send NULL URL)
+    error = ConnectToDebugserver("");
+  } else {
+    error = Status::FromErrorString("connection failed");
   }
   return error;
 }