Author: Charles Zablit
Date: 2026-01-23T13:37:21+01:00
New Revision: 4b7cf46f6bd1bcd3f908efaedfeea27b28b6d564

URL: 
https://github.com/llvm/llvm-project/commit/4b7cf46f6bd1bcd3f908efaedfeea27b28b6d564
DIFF: 
https://github.com/llvm/llvm-project/commit/4b7cf46f6bd1bcd3f908efaedfeea27b28b6d564.diff

LOG: [lldb][windows] add STDIN and STDOUT forwarding support (#175812)

Added: 
    

Modified: 
    lldb/include/lldb/Host/windows/ProcessLauncherWindows.h
    lldb/include/lldb/Host/windows/PseudoConsole.h
    lldb/source/Host/windows/ProcessLauncherWindows.cpp
    lldb/source/Host/windows/PseudoConsole.cpp
    lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
    lldb/test/Shell/Settings/TestFrameFormatColor.test
    lldb/test/Shell/Settings/TestFrameFormatNoColor.test

Removed: 
    


################################################################################
diff  --git a/lldb/include/lldb/Host/windows/ProcessLauncherWindows.h 
b/lldb/include/lldb/Host/windows/ProcessLauncherWindows.h
index b835885dd47c6..7f99a46447966 100644
--- a/lldb/include/lldb/Host/windows/ProcessLauncherWindows.h
+++ b/lldb/include/lldb/Host/windows/ProcessLauncherWindows.h
@@ -11,7 +11,7 @@
 
 #include "lldb/Host/ProcessLauncher.h"
 #include "lldb/Host/windows/windows.h"
-#include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/Error.h"
 
 namespace lldb_private {
 
@@ -38,6 +38,13 @@ class ProcThreadAttributeList {
   static llvm::ErrorOr<ProcThreadAttributeList>
   Create(STARTUPINFOEXW &startupinfoex);
 
+  /// Setup the PseudoConsole handle in the underlying
+  /// LPPROC_THREAD_ATTRIBUTE_LIST.
+  ///
+  /// \param hPC
+  ///     The handle to the PseudoConsole.
+  llvm::Error SetupPseudoConsole(HPCON hPC);
+
   ~ProcThreadAttributeList() {
     if (lpAttributeList) {
       DeleteProcThreadAttributeList(lpAttributeList);

diff  --git a/lldb/include/lldb/Host/windows/PseudoConsole.h 
b/lldb/include/lldb/Host/windows/PseudoConsole.h
index 039783985c025..7a9829e23a097 100644
--- a/lldb/include/lldb/Host/windows/PseudoConsole.h
+++ b/lldb/include/lldb/Host/windows/PseudoConsole.h
@@ -61,6 +61,16 @@ class PseudoConsole {
   ///     invalid.
   HANDLE GetSTDINHandle() const { return m_conpty_input; };
 
+  /// Drains initialization sequences from the ConPTY output pipe.
+  ///
+  /// When a process first attaches to a ConPTY, Windows emits VT100/ANSI 
escape
+  /// sequences (ESC[2J for clear screen, ESC[H for cursor home and more) as
+  /// part of the PseudoConsole initialization. To prevent these sequences from
+  /// appearing in the debugger output (and flushing lldb's shell for instance)
+  /// we launch a short-lived dummy process that triggers the initialization,
+  /// then drain all output before launching the actual debuggee.
+  llvm::Error DrainInitSequences();
+
 protected:
   HANDLE m_conpty_handle = ((HANDLE)(long long)-1);
   HANDLE m_conpty_output = ((HANDLE)(long long)-1);

diff  --git a/lldb/source/Host/windows/ProcessLauncherWindows.cpp 
b/lldb/source/Host/windows/ProcessLauncherWindows.cpp
index 76feceadf46f3..907f0fc86bd89 100644
--- a/lldb/source/Host/windows/ProcessLauncherWindows.cpp
+++ b/lldb/source/Host/windows/ProcessLauncherWindows.cpp
@@ -106,6 +106,15 @@ ProcThreadAttributeList::Create(STARTUPINFOEXW 
&startupinfoex) {
   return ProcThreadAttributeList(startupinfoex.lpAttributeList);
 }
 
+llvm::Error ProcThreadAttributeList::SetupPseudoConsole(HPCON hPC) {
+  BOOL ok = UpdateProcThreadAttribute(lpAttributeList, 0,
+                                      PROC_THREAD_ATTRIBUTE_PSEUDOCONSOLE, hPC,
+                                      sizeof(hPC), NULL, NULL);
+  if (!ok)
+    return llvm::errorCodeToError(llvm::mapWindowsError(GetLastError()));
+  return llvm::Error::success();
+}
+
 HostProcess
 ProcessLauncherWindows::LaunchProcess(const ProcessLaunchInfo &launch_info,
                                       Status &error) {
@@ -116,9 +125,8 @@ ProcessLauncherWindows::LaunchProcess(const 
ProcessLaunchInfo &launch_info,
   startupinfoex.StartupInfo.dwFlags |= STARTF_USESTDHANDLES;
 
   HPCON hPC = launch_info.GetPTY().GetPseudoTerminalHandle();
-  bool use_pty = hPC != INVALID_HANDLE_VALUE &&
-                 launch_info.GetNumFileActions() == 0 &&
-                 launch_info.GetFlags().Test(lldb::eLaunchFlagLaunchInTTY);
+  bool use_pty =
+      hPC != INVALID_HANDLE_VALUE && launch_info.GetNumFileActions() == 0;
 
   HANDLE stdin_handle = GetStdioHandle(launch_info, STDIN_FILENO);
   HANDLE stdout_handle = GetStdioHandle(launch_info, STDOUT_FILENO);
@@ -137,15 +145,15 @@ ProcessLauncherWindows::LaunchProcess(const 
ProcessLaunchInfo &launch_info,
     error = attributelist_or_err.getError();
     return HostProcess();
   }
+  ProcThreadAttributeList attributelist = std::move(*attributelist_or_err);
+
   llvm::scope_exit delete_attributelist(
       [&] { DeleteProcThreadAttributeList(startupinfoex.lpAttributeList); });
 
   std::vector<HANDLE> inherited_handles;
   if (use_pty) {
-    if (!UpdateProcThreadAttribute(startupinfoex.lpAttributeList, 0,
-                                   PROC_THREAD_ATTRIBUTE_PSEUDOCONSOLE, hPC,
-                                   sizeof(hPC), NULL, NULL)) {
-      error = Status(::GetLastError(), eErrorTypeWin32);
+    if (auto err = attributelist.SetupPseudoConsole(hPC)) {
+      error = Status::FromError(std::move(err));
       return HostProcess();
     }
   } else {
@@ -199,7 +207,7 @@ ProcessLauncherWindows::LaunchProcess(const 
ProcessLaunchInfo &launch_info,
 
   BOOL result = ::CreateProcessW(
       wexecutable.c_str(), pwcommandLine, NULL, NULL,
-      /*bInheritHandles=*/!inherited_handles.empty(), flags, 
environment.data(),
+      /*bInheritHandles=*/TRUE, flags, environment.data(),
       wworkingDirectory.size() == 0 ? NULL : wworkingDirectory.c_str(),
       reinterpret_cast<STARTUPINFOW *>(&startupinfoex), &pi);
 

diff  --git a/lldb/source/Host/windows/PseudoConsole.cpp 
b/lldb/source/Host/windows/PseudoConsole.cpp
index b3314fd58bbb8..413c8a3328445 100644
--- a/lldb/source/Host/windows/PseudoConsole.cpp
+++ b/lldb/source/Host/windows/PseudoConsole.cpp
@@ -11,6 +11,7 @@
 #include <mutex>
 
 #include "lldb/Host/windows/PipeWindows.h"
+#include "lldb/Host/windows/ProcessLauncherWindows.h"
 #include "lldb/Host/windows/windows.h"
 #include "lldb/Utility/LLDBLog.h"
 
@@ -118,6 +119,12 @@ llvm::Error PseudoConsole::OpenPseudoConsole() {
   m_conpty_output = hOutputRead;
   m_conpty_input = hInputWrite;
 
+  if (auto error = DrainInitSequences()) {
+    Log *log = GetLog(LLDBLog::Host);
+    LLDB_LOG_ERROR(log, std::move(error),
+                   "failed to finalize ConPTY's setup: {0}");
+  }
+
   return llvm::Error::success();
 }
 
@@ -133,3 +140,62 @@ void PseudoConsole::Close() {
   m_conpty_input = INVALID_HANDLE_VALUE;
   m_conpty_output = INVALID_HANDLE_VALUE;
 }
+
+llvm::Error PseudoConsole::DrainInitSequences() {
+  STARTUPINFOEXW startupinfoex = {};
+  startupinfoex.StartupInfo.cb = sizeof(STARTUPINFOEXW);
+  startupinfoex.StartupInfo.dwFlags |= STARTF_USESTDHANDLES;
+
+  auto attributelist_or_err = ProcThreadAttributeList::Create(startupinfoex);
+  if (!attributelist_or_err)
+    return llvm::errorCodeToError(attributelist_or_err.getError());
+  ProcThreadAttributeList attributelist = std::move(*attributelist_or_err);
+  if (auto error = attributelist.SetupPseudoConsole(m_conpty_handle))
+    return error;
+
+  PROCESS_INFORMATION pi = {};
+
+  wchar_t comspec[MAX_PATH];
+  DWORD comspecLen = GetEnvironmentVariableW(L"COMSPEC", comspec, MAX_PATH);
+  if (comspecLen == 0 || comspecLen >= MAX_PATH)
+    return llvm::createStringError(
+        std::error_code(GetLastError(), std::system_category()),
+        "Failed to get the 'COMSPEC' environment variable");
+
+  std::wstring cmdline_str = std::wstring(comspec) + L" /c 'echo foo && exit'";
+  std::vector<wchar_t> cmdline(cmdline_str.begin(), cmdline_str.end());
+  cmdline.push_back(L'\0');
+
+  if (!CreateProcessW(/*lpApplicationName=*/comspec, cmdline.data(),
+                      /*lpProcessAttributes=*/NULL, 
/*lpThreadAttributes=*/NULL,
+                      /*bInheritHandles=*/TRUE,
+                      /*dwCreationFlags=*/EXTENDED_STARTUPINFO_PRESENT |
+                          CREATE_UNICODE_ENVIRONMENT,
+                      /*lpEnvironment=*/NULL, /*lpCurrentDirectory=*/NULL,
+                      /*lpStartupInfo=*/
+                      reinterpret_cast<STARTUPINFOW *>(&startupinfoex),
+                      /*lpProcessInformation=*/&pi))
+    return llvm::errorCodeToError(
+        std::error_code(GetLastError(), std::system_category()));
+
+  char buf[4096];
+  OVERLAPPED ov = {};
+  ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
+
+  DWORD read;
+  ReadFile(m_conpty_output, buf, sizeof(buf), &read, &ov);
+
+  WaitForSingleObject(pi.hProcess, INFINITE);
+
+  if (GetOverlappedResult(m_conpty_output, &ov, &read, FALSE) && read > 0) {
+    ResetEvent(ov.hEvent);
+    ReadFile(m_conpty_output, buf, sizeof(buf), &read, &ov);
+  }
+
+  CancelIo(m_conpty_output);
+  CloseHandle(ov.hEvent);
+  CloseHandle(pi.hProcess);
+  CloseHandle(pi.hThread);
+
+  return llvm::Error::success();
+}

diff  --git a/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp 
b/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
index 226cc147aadae..373729c952071 100644
--- a/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/ProcessWindows.cpp
@@ -958,21 +958,60 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
                   IOHandler::Type::ProcessIO),
         m_process(process),
         m_read_file(GetInputFD(), File::eOpenOptionReadOnly, false),
-        m_write_file(conpty_input) {
-    m_pipe.CreateNew();
+        m_write_file(conpty_input),
+        m_interrupt_event(
+            CreateEvent(/*lpEventAttributes=*/NULL, /*bManualReset=*/FALSE,
+                        /*bInitialState=*/FALSE, /*lpName=*/NULL)) {}
+
+  ~IOHandlerProcessSTDIOWindows() override {
+    if (m_interrupt_event != INVALID_HANDLE_VALUE)
+      ::CloseHandle(m_interrupt_event);
   }
 
-  ~IOHandlerProcessSTDIOWindows() override = default;
-
   void SetIsRunning(bool running) {
     std::lock_guard<std::mutex> guard(m_mutex);
     SetIsDone(!running);
     m_is_running = running;
   }
 
+  /// Peek the console for input. If it has any, drain the pipe until text 
input
+  /// is found or the pipe is empty.
+  ///
+  /// \param hStdin
+  ///     The handle to the standard input's pipe.
+  ///
+  /// \return
+  ///     true if the pipe has text input.
+  llvm::Expected<bool> ConsoleHasTextInput(const HANDLE hStdin) {
+    // Check if there are already characters buffered. Pressing enter counts as
+    // 2 characters '\r\n' and only one of them is a keyDown event.
+    DWORD bytesAvailable = 0;
+    if (PeekNamedPipe(hStdin, NULL, 0, NULL, &bytesAvailable, NULL)) {
+      if (bytesAvailable > 0)
+        return true;
+    }
+
+    while (true) {
+      INPUT_RECORD inputRecord;
+      DWORD numRead = 0;
+      if (!PeekConsoleInput(hStdin, &inputRecord, 1, &numRead))
+        return llvm::createStringError("Failed to peek standard input.");
+
+      if (numRead == 0)
+        return false;
+
+      if (inputRecord.EventType == KEY_EVENT &&
+          inputRecord.Event.KeyEvent.bKeyDown &&
+          inputRecord.Event.KeyEvent.uChar.AsciiChar != 0)
+        return true;
+
+      if (!ReadConsoleInput(hStdin, &inputRecord, 1, &numRead))
+        return llvm::createStringError("Failed to read standard input.");
+    }
+  }
+
   void Run() override {
-    if (!m_read_file.IsValid() || m_write_file == INVALID_HANDLE_VALUE ||
-        !m_pipe.CanRead() || !m_pipe.CanWrite()) {
+    if (!m_read_file.IsValid() || m_write_file == INVALID_HANDLE_VALUE) {
       SetIsDone(true);
       return;
     }
@@ -980,9 +1019,18 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
     SetIsDone(false);
     SetIsRunning(true);
 
-    HANDLE hStdin = (HANDLE)_get_osfhandle(m_read_file.GetDescriptor());
-    HANDLE hInterrupt = (HANDLE)_get_osfhandle(m_pipe.GetReadFileDescriptor());
-    HANDLE waitHandles[2] = {hStdin, hInterrupt};
+    HANDLE hStdin = m_read_file.GetWaitableHandle();
+    HANDLE waitHandles[2] = {hStdin, m_interrupt_event};
+
+    DWORD consoleMode;
+    bool isConsole = GetConsoleMode(hStdin, &consoleMode) != 0;
+    // With ENABLE_LINE_INPUT, ReadFile returns only when a carriage return is
+    // read. This will block lldb in ReadFile until the user hits enter. Save
+    // the previous console mode to restore it later and remove
+    // ENABLE_LINE_INPUT.
+    DWORD oldConsoleMode = consoleMode;
+    SetConsoleMode(hStdin,
+                   consoleMode & ~ENABLE_LINE_INPUT & ~ENABLE_ECHO_INPUT);
 
     while (true) {
       {
@@ -996,6 +1044,20 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
       case WAIT_FAILED:
         goto exit_loop;
       case WAIT_OBJECT_0: {
+        if (isConsole) {
+          auto hasInputOrErr = ConsoleHasTextInput(hStdin);
+          if (!hasInputOrErr) {
+            Log *log = GetLog(WindowsLog::Process);
+            LLDB_LOG_ERROR(log, hasInputOrErr.takeError(),
+                           "failed to process debuggee's IO: {0}");
+            goto exit_loop;
+          }
+
+          // If no text input is ready, go back to waiting.
+          if (!*hasInputOrErr)
+            continue;
+        }
+
         char ch = 0;
         DWORD read = 0;
         if (!ReadFile(hStdin, &ch, 1, &read, nullptr) || read != 1)
@@ -1007,14 +1069,10 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
         break;
       }
       case WAIT_OBJECT_0 + 1: {
-        char ch = 0;
-        DWORD read = 0;
-        if (!ReadFile(hInterrupt, &ch, 1, &read, nullptr) || read != 1)
-          goto exit_loop;
-
-        if (ch == eControlOpQuit)
+        ControlOp op = m_pending_op.exchange(eControlOpNone);
+        if (op == eControlOpQuit)
           goto exit_loop;
-        if (ch == eControlOpInterrupt &&
+        if (op == eControlOpInterrupt &&
             StateIsRunningState(m_process->GetState()))
           m_process->SendAsyncInterrupt();
         break;
@@ -1026,24 +1084,24 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
 
   exit_loop:;
     SetIsRunning(false);
+    SetIsDone(true);
+    SetConsoleMode(hStdin, oldConsoleMode);
   }
 
   void Cancel() override {
     std::lock_guard<std::mutex> guard(m_mutex);
     SetIsDone(true);
     if (m_is_running) {
-      char ch = eControlOpQuit;
-      if (llvm::Error err = m_pipe.Write(&ch, 1).takeError()) {
-        LLDB_LOG_ERROR(GetLog(LLDBLog::Process), std::move(err),
-                       "Pipe write failed: {0}");
-      }
+      m_pending_op.store(eControlOpQuit);
+      ::SetEvent(m_interrupt_event);
     }
   }
 
   bool Interrupt() override {
     if (m_active) {
-      char ch = eControlOpInterrupt;
-      return !errorToBool(m_pipe.Write(&ch, 1).takeError());
+      m_pending_op.store(eControlOpInterrupt);
+      ::SetEvent(m_interrupt_event);
+      return true;
     }
     if (StateIsRunningState(m_process->GetState())) {
       m_process->SendAsyncInterrupt();
@@ -1055,19 +1113,21 @@ class IOHandlerProcessSTDIOWindows : public IOHandler {
   void GotEOF() override {}
 
 private:
-  Process *m_process;
-  NativeFile m_read_file; // Read from this file (usually actual STDIN for LLDB
-  HANDLE m_write_file =
-      INVALID_HANDLE_VALUE; // Write to this file (usually the primary pty for
-                            // getting io to debuggee)
-  Pipe m_pipe;
-  std::mutex m_mutex;
-  bool m_is_running = false;
-
   enum ControlOp : char {
     eControlOpQuit = 'q',
     eControlOpInterrupt = 'i',
+    eControlOpNone = 0,
   };
+
+  Process *m_process;
+  /// Read from this file (usually actual STDIN for LLDB)
+  NativeFile m_read_file;
+  /// Write to this file (usually the primary pty for getting io to debuggee)
+  HANDLE m_write_file = INVALID_HANDLE_VALUE;
+  HANDLE m_interrupt_event = INVALID_HANDLE_VALUE;
+  std::atomic<ControlOp> m_pending_op{eControlOpNone};
+  std::mutex m_mutex;
+  bool m_is_running = false;
 };
 
 void ProcessWindows::SetPseudoConsoleHandle(

diff  --git a/lldb/test/Shell/Settings/TestFrameFormatColor.test 
b/lldb/test/Shell/Settings/TestFrameFormatColor.test
index 970d7238e7512..f30dafadf5919 100644
--- a/lldb/test/Shell/Settings/TestFrameFormatColor.test
+++ b/lldb/test/Shell/Settings/TestFrameFormatColor.test
@@ -9,4 +9,4 @@ c
 q
 
 # Check the ASCII escape code
-# CHECK: 
+# CHECK: {{\[[0-9;]+m}}

diff  --git a/lldb/test/Shell/Settings/TestFrameFormatNoColor.test 
b/lldb/test/Shell/Settings/TestFrameFormatNoColor.test
index 2bcdb8e82bd9d..37906311c4f69 100644
--- a/lldb/test/Shell/Settings/TestFrameFormatNoColor.test
+++ b/lldb/test/Shell/Settings/TestFrameFormatNoColor.test
@@ -9,4 +9,4 @@ c
 q
 
 # Check the ASCII escape code
-# CHECK-NOT: 
+# CHECK-NOT: {{\[[0-9;]+m}}


        
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