[Lldb-commits] [lldb] [lldb][windows] use OutputDebugStringA instead of c to log events (PR #156474)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

<details>
<summary>Changes</summary>

In https://github.com/llvm/llvm-project/pull/150213 we made use of the Event Viewer on Windows (equivalent of system logging on Darwin) rather than piping to the standard output. This turned out to be too verbose in practice, as the Event Viewer is developer oriented and not user oriented.

This patch swaps the use of `ReportEventW` for `OutputDebugStringA`, allowing to use tools such as `DebugView` to record logs when we are interested in receiving them, rather than continuously writing to the buffer. Please see an example below:
<img width="1253" height="215" alt="Screenshot 2025-09-02 at 16 07 03" src="https://github.com/user-attachments/assets/4a326e46-d8a4-4c99-8c96-1bee62da8d55" />




---
Full diff: https://github.com/llvm/llvm-project/pull/156474.diff


1 Files Affected:

- (modified) lldb/source/Host/windows/Host.cpp (+10-36) 


``````````diff
diff --git a/lldb/source/Host/windows/Host.cpp b/lldb/source/Host/windows/Host.cpp
index 4277b8edb38e5..e8973a3fb937a 100644
--- a/lldb/source/Host/windows/Host.cpp
+++ b/lldb/source/Host/windows/Host.cpp
@@ -22,10 +22,8 @@
 #include "lldb/Utility/StreamString.h"
 #include "lldb/Utility/StructuredData.h"
 
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ConvertUTF.h"
-#include "llvm/Support/ManagedStatic.h"
 
 // Windows includes
 #include <tlhelp32.h>
@@ -308,52 +306,28 @@ Environment Host::GetEnvironment() {
   return env;
 }
 
-/// Manages the lifecycle of a Windows Event's Source.
-/// The destructor will call DeregisterEventSource.
-/// This class is meant to be used with \ref llvm::ManagedStatic.
-class WindowsEventLog {
-public:
-  WindowsEventLog() : handle(RegisterEventSource(nullptr, L"lldb")) {}
-
-  ~WindowsEventLog() {
-    if (handle)
-      DeregisterEventSource(handle);
-  }
-
-  HANDLE GetHandle() const { return handle; }
-
-private:
-  HANDLE handle;
-};
-
-static llvm::ManagedStatic<WindowsEventLog> event_log;
-
 void Host::SystemLog(Severity severity, llvm::StringRef message) {
   if (message.empty())
     return;
 
-  HANDLE h = event_log->GetHandle();
-  if (!h)
-    return;
-
-  llvm::SmallVector<wchar_t, 1> argsUTF16;
-  if (UTF8ToUTF16(message.str(), argsUTF16))
-    return;
+  std::string log_msg;
+  llvm::raw_string_ostream stream(log_msg);
 
-  WORD event_type;
   switch (severity) {
   case lldb::eSeverityWarning:
-    event_type = EVENTLOG_WARNING_TYPE;
+    stream << "[Warning] ";
     break;
   case lldb::eSeverityError:
-    event_type = EVENTLOG_ERROR_TYPE;
+    stream << "[Error] ";
     break;
   case lldb::eSeverityInfo:
   default:
-    event_type = EVENTLOG_INFORMATION_TYPE;
+    stream << "[Info] ";
+    break;
   }
 
-  LPCWSTR messages[1] = {argsUTF16.data()};
-  ReportEventW(h, event_type, 0, 0, nullptr, std::size(messages), 0, messages,
-               nullptr);
+  stream << message;
+  stream.flush();
+
+  OutputDebugStringA(log_msg.c_str());
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/156474