[Lldb-commits] [lldb] [lldb][Windows] Surface DebugBreakProcess Halt() as a SIGSTOP signal stop (PR #201885)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

<details>
<summary>Changes</summary>

With #<!-- -->201884, each keystroke arriving while the debuggee is running triggers a `\x03` BREAK. On Windows, the halt is implemented by injecting a thread that fires an int3. However, the resulting breakpoint exception was being reported as a real `__debugbreak()` (SIGTRAP). The client treats that as a genuine stop, ends the continue, and stdin forwarding ships at most one byte per BP hit.

With this patch, when a halt is pending, the server treats the next breakpoint as the halt acknowledgement and report it as SIGSTOP instead of SIGTRAP. The client then resumes the debuggee automatically, making the brief halt transparent.

---
Full diff: https://github.com/llvm/llvm-project/pull/201885.diff


2 Files Affected:

- (modified) lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp (+34-2) 
- (modified) lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.h (+3) 


``````````diff
diff --git a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
index b235ab281bad6..7c4e6ebe25fee 100644
--- a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
@@ -173,8 +173,13 @@ NativeProcessWindows::GetThreadByID(lldb::tid_t thread_id) {
 Status NativeProcessWindows::Halt() {
   bool caused_stop = false;
   StateType state = GetState();
-  if (state != eStateStopped)
-    return HaltProcess(caused_stop);
+  if (state != eStateStopped) {
+    m_pending_halt = true;
+    Status err = HaltProcess(caused_stop);
+    if (err.Fail() || !caused_stop)
+      m_pending_halt = false;
+    return err;
+  }
   return Status();
 }
 
@@ -581,6 +586,33 @@ NativeProcessWindows::HandleBreakpointException(const ExceptionRecord &record) {
   // Any remaining STATUS_BREAKPOINT is a breakpoint instruction in the
   // program's own code (e.g. `__debugbreak()` or `__builtin_debugtrap()`).
   // Stop the debugger and let the user decide what to do.
+  if (m_pending_halt) {
+    LLDB_LOG(log,
+             "DebugBreakProcess injection treated as Halt SIGSTOP for tid "
+             "{0:x}",
+             thread_id);
+    m_pending_halt = false;
+    ThreadStopInfo signal_info;
+    signal_info.reason = StopReason::eStopReasonSignal;
+    signal_info.signo = 19; // SIGSTOP on POSIX
+
+    // Halt all threads at the kernel level.
+    for (uint32_t i = 0; i < m_threads.size(); ++i) {
+      auto t = static_cast<NativeThreadWindows *>(m_threads[i].get());
+      if (t->DoStop().Fail())
+        exit(1);
+    }
+    if (!m_threads.empty()) {
+      auto first = static_cast<NativeThreadWindows *>(m_threads[0].get());
+      first->SetStopReason(signal_info, "interrupt");
+    }
+    SetCurrentThreadID(thread_id);
+    if (NativeThreadWindows *injected = GetThreadByID(thread_id))
+      injected->SetStopReason(signal_info, "interrupt");
+    SetState(eStateStopped, true);
+    return ExceptionResult::BreakInDebugger;
+  }
+
   std::string desc = formatv("Exception {0:x8} encountered at address {1:x8}",
                              record.GetExceptionCode(), exception_addr)
                          .str();
diff --git a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.h b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.h
index 95b85754ebdeb..02002d57eecaa 100644
--- a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.h
+++ b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.h
@@ -160,6 +160,9 @@ class NativeProcessWindows : public NativeProcessProtocol,
   /// launch / attach.
   bool m_initial_stop_seen = false;
 
+  /// Set when Halt() / Interrupt() schedules a DebugBreakProcess injection.
+  bool m_pending_halt = false;
+
   /// PseudoConsole for the lldb-server stdio-forwarding path.
   std::shared_ptr<PseudoConsole> m_pty;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/201885