[Lldb-commits] [lldb] f0c8198 - [lldb][windows] use OutputDebugStringA instead of c to log events (#156474)

[via lldb-commits]

Author: Charles Zablit
Date: 2025-09-02T18:06:15+01:00
New Revision: f0c819868dddc844f7539c532acfc4b7ab956bbe

URL: https://github.com/llvm/llvm-project/commit/f0c819868dddc844f7539c532acfc4b7ab956bbe
DIFF: https://github.com/llvm/llvm-project/commit/f0c819868dddc844f7539c532acfc4b7ab956bbe.diff

LOG: [lldb][windows] use OutputDebugStringA instead of c to log events (#156474)

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"
/>

Added: 
    

Modified: 
    lldb/source/Host/windows/Host.cpp

Removed: 
    


################################################################################
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());
 }