[lldb] Implement basic support for reverse-continue

lldb/include/lldb/API/SBProcess.h

@@ -159,6 +159,7 @@ class LLDB_API SBProcess {
   lldb::SBError Destroy();
 
   lldb::SBError Continue();
+  lldb::SBError Continue(RunDirection direction);
 
   lldb::SBError Stop();
 

lldb/include/lldb/Target/Process.h

@@ -857,10 +857,10 @@ class Process : public std::enable_shared_from_this<Process>,
   /// \see Thread:Resume()
   /// \see Thread:Step()
   /// \see Thread:Suspend()
-  Status Resume();
+  Status Resume(lldb::RunDirection direction = lldb::eRunForward);
 
   /// Resume a process, and wait for it to stop.
-  Status ResumeSynchronous(Stream *stream);
+  Status ResumeSynchronous(Stream *stream, lldb::RunDirection direction = lldb::eRunForward);
 
   /// Halts a running process.
   ///
@@ -1104,9 +1104,14 @@ class Process : public std::enable_shared_from_this<Process>,
   /// \see Thread:Resume()
   /// \see Thread:Step()
   /// \see Thread:Suspend()
-  virtual Status DoResume() {
-    return Status::FromErrorStringWithFormatv(
-        "error: {0} does not support resuming processes", GetPluginName());
+  virtual Status DoResume(lldb::RunDirection direction) {
+    if (direction == lldb::RunDirection::eRunForward) {
+      return Status::FromErrorStringWithFormatv(
+          "error: {0} does not support resuming processes", GetPluginName());
+    } else {
+      return Status::FromErrorStringWithFormatv(
+          "error: {0} does not support reverse execution of processes", GetPluginName());
+    }
   }
 
   /// Called after resuming a process.
@@ -2332,6 +2337,8 @@ class Process : public std::enable_shared_from_this<Process>,
 
   bool IsRunning() const;
 
+  lldb::RunDirection GetLastRunDirection() { return m_last_run_direction; }
+
   DynamicCheckerFunctions *GetDynamicCheckers() {
     return m_dynamic_checkers_up.get();
   }
@@ -2851,7 +2858,7 @@ void PruneThreadPlans();
   ///
   /// \return
   ///     An Status object describing the success or failure of the resume.
-  Status PrivateResume();
+  Status PrivateResume(lldb::RunDirection direction = lldb::eRunForward);
 
   // Called internally
   void CompleteAttach();
@@ -3127,6 +3134,8 @@ void PruneThreadPlans();
                            // m_currently_handling_do_on_removals are true,
                            // Resume will only request a resume, using this
                            // flag to check.
+  // The direction of execution from the last time this process was resumed.
+  lldb::RunDirection m_last_run_direction;
 
   lldb::tid_t m_interrupt_tid; /// The tid of the thread that issued the async
                                /// interrupt, used by thread plan timeout. It

lldb/include/lldb/Target/StopInfo.h

@@ -142,6 +142,12 @@ class StopInfo : public std::enable_shared_from_this<StopInfo> {
   static lldb::StopInfoSP
   CreateStopReasonProcessorTrace(Thread &thread, const char *description);
 
+  // This creates a StopInfo indicating that execution stopped because
+  // it was replaying some recorded execution history, and execution reached
+  // the end of that recorded history.
+  static lldb::StopInfoSP
+  CreateStopReasonHistoryBoundary(Thread &thread, const char *description);
+
   static lldb::StopInfoSP CreateStopReasonFork(Thread &thread,
                                                lldb::pid_t child_pid,
                                                lldb::tid_t child_tid);

lldb/include/lldb/lldb-enumerations.h

@@ -135,6 +135,9 @@ FLAGS_ENUM(LaunchFlags){
 /// Thread Run Modes.
 enum RunMode { eOnlyThisThread, eAllThreads, eOnlyDuringStepping };
 
+/// Execution directions
+enum RunDirection { eRunForward, eRunReverse };
+
 /// Byte ordering definitions.
 enum ByteOrder {
   eByteOrderInvalid = 0,
@@ -254,6 +257,9 @@ enum StopReason {
   eStopReasonVFork,
   eStopReasonVForkDone,
   eStopReasonInterrupt, ///< Thread requested interrupt
+  // Indicates that execution stopped because the debugger backend relies
+  // on recorded data and we reached the end of that data.
+  eStopReasonHistoryBoundary,
 };
 
 /// Command Return Status Types.

lldb/packages/Python/lldbsuite/test/gdbclientutils.py

@@ -510,8 +510,9 @@ def start(self):
         self._thread.start()
 
     def stop(self):
-        self._thread.join()
-        self._thread = None
+        if self._thread is not None:
+            self._thread.join()
+            self._thread = None
 
     def get_connect_address(self):
         return self._socket.get_connect_address()

lldb/packages/Python/lldbsuite/test/lldbgdbproxy.py

@@ -0,0 +1,175 @@
+import logging
+import os
+import os.path
+import random
+
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.gdbclientutils import *
+import lldbgdbserverutils
+from lldbsuite.support import seven
+
+
+class GDBProxyTestBase(TestBase):
+    """
+    Base class for gdbserver proxy tests.
+
+    This class will setup and start a mock GDB server for the test to use.
+    It pases through requests to a regular lldb-server/debugserver and
+    forwards replies back to the LLDB under test.
+    """
+
+    """The gdbserver that we implement."""
+    server = None
+    """The inner lldb-server/debugserver process that we proxy requests into."""
+    monitor_server = None
+    monitor_sock = None
+
+    server_socket_class = TCPServerSocket
+
+    DEFAULT_TIMEOUT = 20 * (10 if ("ASAN_OPTIONS" in os.environ) else 1)
+
+    _verbose_log_handler = None
+    _log_formatter = logging.Formatter(fmt="%(asctime)-15s %(levelname)-8s %(message)s")
+
+    def setUpBaseLogging(self):
+        self.logger = logging.getLogger(__name__)
+
+        if len(self.logger.handlers) > 0:
+            return  # We have set up this handler already
+
+        self.logger.propagate = False
+        self.logger.setLevel(logging.DEBUG)
+
+        # log all warnings to stderr
+        handler = logging.StreamHandler()
+        handler.setLevel(logging.WARNING)
+        handler.setFormatter(self._log_formatter)
+        self.logger.addHandler(handler)
+
+    def setUp(self):
+        TestBase.setUp(self)
+
+        self.setUpBaseLogging()
+
+        if self.isVerboseLoggingRequested():
+            # If requested, full logs go to a log file
+            log_file_name = self.getLogBasenameForCurrentTest() + "-proxy.log"
+            self._verbose_log_handler = logging.FileHandler(
+               log_file_name
+            )
+            self._verbose_log_handler.setFormatter(self._log_formatter)
+            self._verbose_log_handler.setLevel(logging.DEBUG)
+            self.logger.addHandler(self._verbose_log_handler)
+
+        lldb_server_exe = lldbgdbserverutils.get_lldb_server_exe()
+        if lldb_server_exe is None:
+            self.debug_monitor_exe = lldbgdbserverutils.get_debugserver_exe()
+            self.assertTrue(self.debug_monitor_exe is not None)
+            self.debug_monitor_extra_args = []
+        else:
+            self.debug_monitor_exe = lldb_server_exe
+            self.debug_monitor_extra_args = ["gdbserver"]
+
+        self.server = MockGDBServer(self.server_socket_class())
+        self.server.responder = self
+
+    def tearDown(self):
+        # TestBase.tearDown will kill the process, but we need to kill it early
+        # so its client connection closes and we can stop the server before
+        # finally calling the base tearDown.
+        if self.process() is not None:
+            self.process().Kill()
+        self.server.stop()
+
+        self.logger.removeHandler(self._verbose_log_handler)
+        self._verbose_log_handler = None
+
+        TestBase.tearDown(self)
+
+    def isVerboseLoggingRequested(self):
+        # We will report our detailed logs if the user requested that the "gdb-remote" channel is
+        # logged.
+        return any(("gdb-remote" in channel) for channel in lldbtest_config.channels)
+
+    def connect(self, target):
+        """
+        Create a process by connecting to the mock GDB server.
+        """
+        self.prep_debug_monitor_and_inferior()
+        self.server.start()
+
+        listener = self.dbg.GetListener()
+        error = lldb.SBError()
+        process = target.ConnectRemote(
+            listener, self.server.get_connect_url(), "gdb-remote", error
+        )
+        self.assertTrue(error.Success(), error.description)
+        self.assertTrue(process, PROCESS_IS_VALID)
+        return process
+
+    def get_next_port(self):
+        return 12000 + random.randint(0, 3999)
+
+    def prep_debug_monitor_and_inferior(self):
+        inferior_exe_path = self.getBuildArtifact("a.out")
+        self.connect_to_debug_monitor([inferior_exe_path])
+        self.assertIsNotNone(self.monitor_server)
+        self.initial_handshake()
+
+    def initial_handshake(self):
+        self.monitor_server.send_packet(seven.bitcast_to_bytes("+"))
+        reply = seven.bitcast_to_string(self.monitor_server.get_normal_packet())
+        self.assertEqual(reply, "+")
+        self.monitor_server.send_packet(seven.bitcast_to_bytes("QStartNoAckMode"))
+        reply = seven.bitcast_to_string(self.monitor_server.get_normal_packet())
+        self.assertEqual(reply, "+")
+        reply = seven.bitcast_to_string(self.monitor_server.get_normal_packet())
+        self.assertEqual(reply, "OK")
+        self.monitor_server.send_packet(seven.bitcast_to_bytes("+"))
+        reply = seven.bitcast_to_string(self.monitor_server.get_normal_packet())
+        self.assertEqual(reply, "+")
+
+    def get_debug_monitor_command_line_args(self, connect_address, launch_args):
+        return self.debug_monitor_extra_args + ["--reverse-connect", connect_address] + launch_args
+
+    def launch_debug_monitor(self, launch_args):
+        family, type, proto, _, addr = socket.getaddrinfo(
+            "localhost", 0, proto=socket.IPPROTO_TCP
+        )[0]
+        sock = socket.socket(family, type, proto)
+        sock.settimeout(self.DEFAULT_TIMEOUT)
+        sock.bind(addr)
+        sock.listen(1)
+        addr = sock.getsockname()
+        connect_address = "[{}]:{}".format(*addr)
+
+        commandline_args = self.get_debug_monitor_command_line_args(
+            connect_address, launch_args
+        )
+
+        # Start the server.
+        self.logger.info(f"Spawning monitor {commandline_args}")
+        monitor_process = self.spawnSubprocess(
+            self.debug_monitor_exe, commandline_args, install_remote=False
+        )
+        self.assertIsNotNone(monitor_process)
+
+        self.monitor_sock = sock.accept()[0]
+        self.monitor_sock.settimeout(self.DEFAULT_TIMEOUT)
+        return monitor_process
+
+    def connect_to_debug_monitor(self, launch_args):
+        monitor_process = self.launch_debug_monitor(launch_args)
+        self.monitor_server = lldbgdbserverutils.Server(self.monitor_sock, monitor_process)
+
+    def respond(self, packet):
+        """Subclasses can override this to change how packets are handled."""
+        return self.pass_through(packet)
+
+    def pass_through(self, packet):
+        self.logger.info(f"Sending packet {packet}")
+        self.monitor_server.send_packet(seven.bitcast_to_bytes(packet))
+        reply = seven.bitcast_to_string(self.monitor_server.get_normal_packet())
+        self.logger.info(f"Received reply {reply}")
+        return reply