[lldb][Windows] Use WaitForDebugEventEx if available#196817
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@llvm/pr-subscribers-lldb Author: Nerixyz (Nerixyz) ChangesThis makes use of The two functions are identical except for the handling of Split from #196395. 1 Files Affected:
diff --git a/lldb/source/Plugins/Process/Windows/Common/DebuggerThread.cpp b/lldb/source/Plugins/Process/Windows/Common/DebuggerThread.cpp
index 6359a63dfef91..95e9084b602dd 100644
--- a/lldb/source/Plugins/Process/Windows/Common/DebuggerThread.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/DebuggerThread.cpp
@@ -25,6 +25,7 @@
#include "Plugins/Process/Windows/Common/ProcessWindowsLog.h"
+#include "lldb/Utility/LLDBLog.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/ConvertUTF.h"
#include "llvm/Support/Threading.h"
@@ -40,9 +41,40 @@
using namespace lldb;
using namespace lldb_private;
+typedef BOOL WINAPI WaitForDebugEventFn(LPDEBUG_EVENT, DWORD);
+static WaitForDebugEventFn *g_wait_for_debug_event = nullptr;
+
+static WaitForDebugEventFn *GetWaitForDebugEventEx() {
+ HMODULE h_kernel32 = LoadLibraryW(L"kernel32.dll");
+ if (!h_kernel32) {
+ llvm::Error err = llvm::errorCodeToError(
+ std::error_code(GetLastError(), std::system_category()));
+ LLDB_LOG_ERROR(GetLog(LLDBLog::Host), std::move(err),
+ "Could not load kernel32: {0}");
+ return nullptr;
+ }
+
+ return reinterpret_cast<WaitForDebugEventFn *>(
+ GetProcAddress(h_kernel32, "WaitForDebugEventEx"));
+}
+
+/// WaitForDebugEventEx is only available on Windows 10+. This lazily checks if
+/// the function is available and falls back to WaitForDebugEvent if
+/// unavailable. The -Ex version ensures correct forwarding of
+/// OutputDebugStringW events.
+static void InitializeWaitForDebugEvent() {
+ if (g_wait_for_debug_event)
+ return;
+
+ g_wait_for_debug_event = GetWaitForDebugEventEx();
+ if (!g_wait_for_debug_event)
+ g_wait_for_debug_event = &WaitForDebugEvent;
+}
+
DebuggerThread::DebuggerThread(DebugDelegateSP debug_delegate)
: m_debug_delegate(debug_delegate), m_pid_to_detach(0),
m_is_shutting_down(false) {
+ InitializeWaitForDebugEvent();
m_debugging_ended_event = ::CreateEvent(nullptr, TRUE, FALSE, nullptr);
}
@@ -236,7 +268,7 @@ void DebuggerThread::DebugLoop() {
LLDB_LOG_VERBOSE(log, "Entering WaitForDebugEvent loop");
while (should_debug) {
LLDB_LOG_VERBOSE(log, "Calling WaitForDebugEvent");
- BOOL wait_result = WaitForDebugEvent(&dbe, INFINITE);
+ BOOL wait_result = g_wait_for_debug_event(&dbe, INFINITE);
if (wait_result) {
DWORD continue_status = DBG_CONTINUE;
bool shutting_down = m_is_shutting_down;
@@ -314,7 +346,7 @@ void DebuggerThread::DebugLoop() {
// target threads are running at this time, there is possibility to
// have some breakpoint exception between last WaitForDebugEvent and
// DebugActiveProcessStop but ignore for now.
- while (WaitForDebugEvent(&dbe, 0)) {
+ while (g_wait_for_debug_event(&dbe, 0)) {
continue_status = DBG_CONTINUE;
if (dbe.dwDebugEventCode == EXCEPTION_DEBUG_EVENT &&
!(dbe.u.Exception.ExceptionRecord.ExceptionCode ==
|
|
|
||
| g_wait_for_debug_event = GetWaitForDebugEventEx(); | ||
| if (!g_wait_for_debug_event) | ||
| g_wait_for_debug_event = &WaitForDebugEvent; |
Contributor
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I think we should eventually add a log here to warn the user that unicode won't be supported.
It won't hit on windows 10+ once #196395 lands. However, the log could be useful for users of other versions of Windows.
charles-zablit
approved these changes
May 11, 2026
EuphoricThinking
pushed a commit
to EuphoricThinking/llvm-project
that referenced
this pull request
May 14, 2026
This makes use of [`WaitForDebugEventEx`](https://learn.microsoft.com/en-us/windows/win32/api/debugapi/nf-debugapi-waitfordebugeventex) over `WaitForDebugEvent` if available (Windows 10+). The two functions are identical except for the handling of `OutputDebugStringW`. The `-Ex` version forwards the string as Unicode whereas the other version forwards ASCII strings. Since we don't handle these outputs yet, it shouldn't make any difference. Split from llvm#196395.
pedroMVicente
pushed a commit
to pedroMVicente/llvm-project
that referenced
this pull request
May 19, 2026
This makes use of [`WaitForDebugEventEx`](https://learn.microsoft.com/en-us/windows/win32/api/debugapi/nf-debugapi-waitfordebugeventex) over `WaitForDebugEvent` if available (Windows 10+). The two functions are identical except for the handling of `OutputDebugStringW`. The `-Ex` version forwards the string as Unicode whereas the other version forwards ASCII strings. Since we don't handle these outputs yet, it shouldn't make any difference. Split from llvm#196395.
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This makes use of
WaitForDebugEventExoverWaitForDebugEventif available (Windows 10+).The two functions are identical except for the handling of
OutputDebugStringW. The-Exversion forwards the string as Unicode whereas the other version forwards ASCII strings. Since we don't handle these outputs yet, it shouldn't make any difference.Split from #196395.