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

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit created https://github.com/llvm/llvm-project/pull/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" />




>From ec308302c936c8ce4993ae27f8d5e813e4ac59c9 Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Tue, 2 Sep 2025 16:13:17 +0100
Subject: [PATCH] [lldb][windows] use OutputDebugStringA instead of
 ReportEventW to log events

---
 lldb/source/Host/windows/Host.cpp | 44 +++++--------------------------
 1 file changed, 7 insertions(+), 37 deletions(-)

diff --git a/lldb/source/Host/windows/Host.cpp b/lldb/source/Host/windows/Host.cpp
index 4277b8edb38e5..8be4596c420a4 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 +306,24 @@ 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;
-
-  WORD event_type;
+  std::string log_prefix;
   switch (severity) {
   case lldb::eSeverityWarning:
-    event_type = EVENTLOG_WARNING_TYPE;
+    log_prefix = "[Warning] ";
     break;
   case lldb::eSeverityError:
-    event_type = EVENTLOG_ERROR_TYPE;
+    log_prefix = "[Error] ";
     break;
   case lldb::eSeverityInfo:
   default:
-    event_type = EVENTLOG_INFORMATION_TYPE;
+    log_prefix = "[Info] ";
+    break;
   }
 
-  LPCWSTR messages[1] = {argsUTF16.data()};
-  ReportEventW(h, event_type, 0, 0, nullptr, std::size(messages), 0, messages,
-               nullptr);
+  std::string final_message = log_prefix + message.str();
+  OutputDebugStringA(final_message.c_str());
 }