Switch over to using socketpair for local debugserver connections as they are twice as fast as TCP sockets (on macOS at least).

This change opens a socket pair and passes the second socket pair file descriptor down to the debugserver binary using a new option: "--fd=N" where N is the file descriptor. This file descriptor gets passed via posix_spawn() so that there is no need to do any bind/listen or bind/accept calls and eliminates the hanshake unix socket that is used to pass the result of the actual port that ends up being used so it can save time on launch as well as being faster.

This is currently only enabled on __APPLE__ builds. Other OSs should try modifying the #define from ProcessGDBRemote.cpp but the first person will need to port the --fd option over to lldb-server. Any OSs that enable USE_SOCKETPAIR_FOR_LOCAL_CONNECTION in their native builds can use the socket pair stuff. The #define is Apple only right now, but looks like:

#if defined (__APPLE__)
#define USE_SOCKETPAIR_FOR_LOCAL_CONNECTION 1
#endif

<rdar://problem/27814880> 

llvm-svn: 278524

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

@@ -1091,7 +1091,8 @@ GDBRemoteCommunication::StartDebugserverProcess (const char *url,
                                                  Platform *platform,
                                                  ProcessLaunchInfo &launch_info,
                                                  uint16_t *port,
-                                                 const Args& inferior_args)
+                                                 const Args* inferior_args,
+                                                 int pass_comm_fd)
 {
     Log *log (ProcessGDBRemoteLog::GetLogIfAllCategoriesSet (GDBR_LOG_PROCESS));
     if (log)
@@ -1171,6 +1172,16 @@ GDBRemoteCommunication::StartDebugserverProcess (const char *url,
         if (url)
             debugserver_args.AppendArgument(url);
 
+        if (pass_comm_fd >= 0)
+        {
+            StreamString fd_arg;
+            fd_arg.Printf("--fd=%i", pass_comm_fd);
+            debugserver_args.AppendArgument(fd_arg.GetData());
+            // Send "pass_comm_fd" down to the inferior so it can use it to
+            // communicate back with this process
+            launch_info.AppendDuplicateFileAction(pass_comm_fd, pass_comm_fd);
+        }
+
         // use native registers, not the GDB registers
         debugserver_args.AppendArgument("--native-regs");
 
@@ -1189,7 +1200,7 @@ GDBRemoteCommunication::StartDebugserverProcess (const char *url,
         // port is null when debug server should listen on domain socket -
         // we're not interested in port value but rather waiting for debug server
         // to become available.
-        if ((port != nullptr && *port == 0) || port == nullptr)
+        if (pass_comm_fd == -1 && ((port != nullptr && *port == 0) || port == nullptr))
         {
             if (url)
             {
@@ -1304,10 +1315,10 @@ GDBRemoteCommunication::StartDebugserverProcess (const char *url,
             }
         } while (has_env_var);
 
-        if (inferior_args.GetArgumentCount() > 0)
+        if (inferior_args && inferior_args->GetArgumentCount() > 0)
         {
             debugserver_args.AppendArgument ("--");
-            debugserver_args.AppendArguments (inferior_args);
+            debugserver_args.AppendArguments (*inferior_args);
         }
 
         // Copy the current environment to the gdbserver/debugserver instance
@@ -1337,8 +1348,7 @@ GDBRemoteCommunication::StartDebugserverProcess (const char *url,
         }
         error = Host::LaunchProcess(launch_info);
         
-        if (error.Success() &&
+        if (error.Success() && (launch_info.GetProcessID() != LLDB_INVALID_PROCESS_ID) && pass_comm_fd == -1)
-            launch_info.GetProcessID() != LLDB_INVALID_PROCESS_ID)
         {
             if (named_pipe_path.size() > 0)
             {

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.h

@@ -162,7 +162,8 @@ public:
                             Platform *platform, // If non nullptr, then check with the platform for the GDB server binary if it can't be located
                             ProcessLaunchInfo &launch_info,
                             uint16_t *port,
-                            const Args& inferior_args = Args());
+                            const Args *inferior_args,
+                            int pass_comm_fd); // Communication file descriptor to pass during fork/exec to avoid having to connect/accept
 
     void
     DumpHistory(Stream &strm);

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

@@ -149,7 +149,8 @@ GDBRemoteCommunicationServerPlatform::LaunchGDBServer(const lldb_private::Args&
                                            nullptr,
                                            debugserver_launch_info,
                                            port_ptr,
-                                           args);
+                                           &args,
+                                           -1);
 
     pid = debugserver_launch_info.GetProcessID();
     if (pid != LLDB_INVALID_PROCESS_ID)

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

@@ -16,6 +16,7 @@
 #include <netinet/in.h>
 #include <sys/mman.h>       // for mmap
 #endif
+#include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <time.h>
@@ -64,6 +65,7 @@
 #include "lldb/Target/TargetList.h"
 #include "lldb/Target/ThreadPlanCallFunction.h"
 #include "lldb/Target/SystemRuntime.h"
+#include "lldb/Utility/CleanUp.h"
 #include "lldb/Utility/PseudoTerminal.h"
 
 // Project includes
@@ -3602,6 +3604,23 @@ ProcessGDBRemote::EstablishConnectionIfNeeded (const ProcessInfo &process_info)
     }
     return error;
 }
+#if defined (__APPLE__)
+#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
 
 Error
 ProcessGDBRemote::LaunchAndConnectToDebugserver (const ProcessInfo &process_info)
@@ -3624,30 +3643,34 @@ ProcessGDBRemote::LaunchAndConnectToDebugserver (const ProcessInfo &process_info
                                                           false);
         debugserver_launch_info.SetUserID(process_info.GetUserID());
 
-#if defined (__APPLE__) && (defined (__arm__) || defined (__arm64__) || defined (__aarch64__))
-        // On iOS, still do a local connection using a random port
-        const char *hostname = "127.0.0.1";
-        uint16_t port = get_random_port ();
-#else
-        // Set hostname being NULL to do the reverse connect where debugserver
-        // will bind to port zero and it will communicate back to us the port
-        // that we will connect to
-        const char *hostname = nullptr;
-        uint16_t port = 0;
-#endif
 
-        StreamString url_str;
+        int communication_fd = -1;
-        const char* url = nullptr;
+#ifdef USE_SOCKETPAIR_FOR_LOCAL_CONNECTION
-        if (hostname != nullptr)
+        // Auto close the sockets we might open up unless everything goes OK. This
+        // helps us not leak file descriptors when things go wrong.
+        lldb_utility::CleanUp <int, int> our_socket(-1, -1, close);
+        lldb_utility::CleanUp <int, int> gdb_socket(-1, -1, close);
+
+        // Use a socketpair on Apple for now until other platforms can verify it
+        // works and is fast enough
         {
-            url_str.Printf("%s:%u", hostname, port);
+            int sockets[2]; /* the pair of socket descriptors */
-            url = url_str.GetData();
+            if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) == -1)
+            {
+                error.SetErrorToErrno();
+                return error;
             }
 
-        error = m_gdb_comm.StartDebugserverProcess (url,
+            our_socket.set(sockets[0]);
-                                                    GetTarget().GetPlatform().get(),
+            gdb_socket.set(sockets[1]);
-                                                    debugserver_launch_info,
+        }
-                                                    &port);
+
+        // Don't let any child processes inherit our communication socket
+        SetCloexecFlag(our_socket.get());
+        communication_fd = gdb_socket.get();
+#endif
+
+        error = m_gdb_comm.StartDebugserverProcess(nullptr, GetTarget().GetPlatform().get(), debugserver_launch_info, nullptr, nullptr, communication_fd);
 
         if (error.Success ())
             m_debugserver_pid = debugserver_launch_info.GetProcessID();
@@ -3655,7 +3678,14 @@ ProcessGDBRemote::LaunchAndConnectToDebugserver (const ProcessInfo &process_info
             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
+            m_gdb_comm.SetConnection(new ConnectionFileDescriptor(our_socket.release(), true));
+#endif
             StartAsyncThread ();
+        }
 
         if (error.Fail())
         {
@@ -3669,13 +3699,11 @@ ProcessGDBRemote::LaunchAndConnectToDebugserver (const ProcessInfo &process_info
         if (m_gdb_comm.IsConnected())
         {
             // Finish the connection process by doing the handshake without connecting (send NULL URL)
-            ConnectToDebugserver (NULL);
+            ConnectToDebugserver(NULL);
         }
         else
         {
-            StreamString connect_url;
+            error.SetErrorString("connection failed");
-            connect_url.Printf("connect://%s:%u", hostname, port);
-            error = ConnectToDebugserver (connect_url.GetString().c_str());
         }
 
     }

lldb/tools/debugserver/source/debugserver.cpp

@@ -872,6 +872,7 @@ static struct option g_long_options[] =
     { "working-dir",        required_argument,  NULL,               'W' },  // The working directory that the inferior process should have (only if debugserver launches the process)
     { "platform",           required_argument,  NULL,               'p' },  // Put this executable into a remote platform mode
     { "unix-socket",        required_argument,  NULL,               'u' },  // If we need to handshake with our parent process, an option will be passed down that specifies a unix socket name to use
+    { "fd",                 required_argument,  NULL,            'FDSC' },  // A file descriptor was passed to this process when spawned that is already open and ready for communication
     { "named-pipe",         required_argument,  NULL,               'P' },
     { "reverse-connect",    no_argument,        NULL,               'R' },
     { "env",                required_argument,  NULL,               'e' },  // When debugserver launches the process, set a single environment entry as specified by the option value ("./debugserver -e FOO=1 -e BAR=2 localhost:1234 -- /bin/ls")
@@ -949,6 +950,7 @@ main (int argc, char *argv[])
     int ch;
     int long_option_index = 0;
     int debug = 0;
+    int communication_fd = -1;
     std::string compile_options;
     std::string waitfor_pid_name;           // Wait for a process that starts with this name
     std::string attach_pid_name;
@@ -1248,6 +1250,12 @@ main (int argc, char *argv[])
                         remote->Context().PushEnvironment(env_entry);
                 }
                 break;
+
+            case 'FDSC':
+                // File descriptor passed to this process during fork/exec and is already
+                // open and ready for communication.
+                communication_fd = atoi(optarg);
+                break;
         }
     }
 
@@ -1324,7 +1332,7 @@ main (int argc, char *argv[])
     char str[PATH_MAX];
     str[0] = '\0';
 
-    if (g_lockdown_opt == 0 && g_applist_opt == 0)
+    if (g_lockdown_opt == 0 && g_applist_opt == 0 && communication_fd == -1)
     {
         // Make sure we at least have port
         if (argc < 1)
@@ -1475,6 +1483,15 @@ main (int argc, char *argv[])
                     if (remote->Comm().OpenFile (str))
                         mode = eRNBRunLoopModeExit;
                 }
+                else if (communication_fd >= 0)
+                {
+                    // We were passed a file descriptor to use during fork/exec that is already open
+                    // in our process, so lets just use it!
+                    if (remote->Comm().useFD(communication_fd))
+                        mode = eRNBRunLoopModeExit;
+                    else
+                        remote->StartReadRemoteDataThread();
+                }
 
                 if (mode != eRNBRunLoopModeExit)
                 {
@@ -1600,6 +1617,16 @@ main (int argc, char *argv[])
                         if (remote->Comm().OpenFile (str))
                             mode = eRNBRunLoopModeExit;
                     }
+                    else if (communication_fd >= 0)
+                    {
+                        // We were passed a file descriptor to use during fork/exec that is already open
+                        // in our process, so lets just use it!
+                        if (remote->Comm().useFD(communication_fd))
+                            mode = eRNBRunLoopModeExit;
+                        else
+                            remote->StartReadRemoteDataThread();
+                    }
+
                     if (mode != eRNBRunLoopModeExit)
                         RNBLogSTDOUT ("Waiting for debugger instructions for process %d.\n", attach_pid);
                 }
@@ -1625,6 +1652,15 @@ main (int argc, char *argv[])
                             if (remote->Comm().OpenFile (str))
                                 mode = eRNBRunLoopModeExit;
                         }
+                        else if (communication_fd >= 0)
+                        {
+                            // We were passed a file descriptor to use during fork/exec that is already open
+                            // in our process, so lets just use it!
+                            if (remote->Comm().useFD(communication_fd))
+                                mode = eRNBRunLoopModeExit;
+                            else
+                                remote->StartReadRemoteDataThread();
+                        }
 
                         if (mode != eRNBRunLoopModeExit)
                         {
@@ -1657,6 +1693,15 @@ main (int argc, char *argv[])
                     if (remote->Comm().OpenFile (str))
                         mode = eRNBRunLoopModeExit;
                 }
+                else if (communication_fd >= 0)
+                {
+                    // We were passed a file descriptor to use during fork/exec that is already open
+                    // in our process, so lets just use it!
+                    if (remote->Comm().useFD(communication_fd))
+                        mode = eRNBRunLoopModeExit;
+                    else
+                        remote->StartReadRemoteDataThread();
+                }
 
                 if (mode != eRNBRunLoopModeExit)
                     mode = RNBRunLoopPlatform (remote);