Claude's crazy exception handler hack

Common/ExceptionHandlerSetup.cpp

@@ -15,6 +15,7 @@
 #include "Common/CommonFuncs.h"
 #include "Common/CommonTypes.h"
 #include "Common/Log.h"
+#include "Common/StringUtils.h"
 #include "Common/Thread/ThreadUtil.h"
 #include "Common/MachineContext.h"
 #include "Common/ExceptionHandlerSetup.h"
@@ -27,7 +28,48 @@ static void *altStack = nullptr;
 // We cannot handle exceptions in UWP builds. Bleh.
 #if PPSSPP_PLATFORM(WINDOWS) && !PPSSPP_PLATFORM(UWP)
 
+#include <dbghelp.h>
+#pragma comment(lib, "dbghelp.lib")
+
 static PVOID g_vectoredExceptionHandle;
+static bool g_symInitialized = false;
+static bool g_logCrashStackTrace = false;
+
+// Logs a best-effort stack trace when we're about to let a genuinely unhandled access
+// violation crash the process - e.g. a bad host pointer (not a guest PSP memory access)
+// passed to a CRT function like strlen(). Only meant for diagnostics, so failures here are
+// non-fatal; we just lose the extra info.
+static void LogCrashStackTrace() {
+	void *stack[32]{};
+	USHORT captured = CaptureStackBackTrace(0, (ULONG)ARRAY_SIZE(stack), stack, nullptr);
+
+	ERROR_LOG(Log::System, "Unhandled access violation - stack trace (%d frames):", (int)captured);
+
+	HANDLE process = GetCurrentProcess();
+	char symbolBuffer[sizeof(SYMBOL_INFO) + MAX_SYM_NAME]{};
+	SYMBOL_INFO *symbol = (SYMBOL_INFO *)symbolBuffer;
+	symbol->SizeOfStruct = sizeof(SYMBOL_INFO);
+	symbol->MaxNameLen = MAX_SYM_NAME;
+
+	for (USHORT i = 0; i < captured; i++) {
+		DWORD64 address = (DWORD64)(uintptr_t)stack[i];
+		std::string line = StringFromFormat("  #%d %016llx", (int)i, (unsigned long long)address);
+
+		DWORD64 displacement = 0;
+		if (SymFromAddr(process, address, &displacement, symbol)) {
+			line += StringFromFormat(" %s+0x%llx", symbol->Name, (unsigned long long)displacement);
+		}
+
+		DWORD lineDisplacement = 0;
+		IMAGEHLP_LINE64 lineInfo{};
+		lineInfo.SizeOfStruct = sizeof(lineInfo);
+		if (SymGetLineFromAddr64(process, address, &lineDisplacement, &lineInfo)) {
+			line += StringFromFormat(" (%s:%d)", lineInfo.FileName, (int)lineInfo.LineNumber);
+		}
+
+		ERROR_LOG(Log::System, "%s", line.c_str());
+	}
+}
 
 static LONG NTAPI GlobalExceptionHandler(PEXCEPTION_POINTERS pPtrs) {
 	switch (pPtrs->ExceptionRecord->ExceptionCode) {
@@ -45,6 +87,11 @@ static LONG NTAPI GlobalExceptionHandler(PEXCEPTION_POINTERS pPtrs) {
 		if (g_badAccessHandler(badAddress, ctx)) {
 			return (DWORD)EXCEPTION_CONTINUE_EXECUTION;
 		} else {
+			if (g_logCrashStackTrace) {
+				ERROR_LOG(Log::System, "Unhandled access violation (%s) at address %016llx, pc=%016llx",
+					accessType == 1 ? "write" : "read", (unsigned long long)badAddress, (unsigned long long)(uintptr_t)pPtrs->ExceptionRecord->ExceptionAddress);
+				LogCrashStackTrace();
+			}
 			// Let's not prevent debugging.
 			return (DWORD)EXCEPTION_CONTINUE_SEARCH;
 		}
@@ -75,7 +122,8 @@ static LONG NTAPI GlobalExceptionHandler(PEXCEPTION_POINTERS pPtrs) {
 	}
 }
 
-void InstallExceptionHandler(BadAccessHandler badAccessHandler) {
+void InstallExceptionHandler(BadAccessHandler badAccessHandler, bool logStackTraceOnCrash) {
+	g_logCrashStackTrace = logStackTraceOnCrash;
 	if (g_vectoredExceptionHandle) {
 		g_badAccessHandler = badAccessHandler;
 		return;
@@ -83,6 +131,12 @@ void InstallExceptionHandler(BadAccessHandler badAccessHandler) {
 
 	INFO_LOG(Log::System, "Installing exception handler");
 	g_badAccessHandler = badAccessHandler;
+
+	if (logStackTraceOnCrash && !g_symInitialized) {
+		SymSetOptions(SYMOPT_LOAD_LINES | SYMOPT_DEFERRED_LOADS | SYMOPT_UNDNAME);
+		g_symInitialized = SymInitialize(GetCurrentProcess(), nullptr, TRUE) != FALSE;
+	}
+
 #ifdef USE_ASAN
 	g_vectoredExceptionHandle = AddVectoredExceptionHandler(FALSE, GlobalExceptionHandler);
 #else
@@ -182,7 +236,7 @@ static void ExceptionThread(mach_port_t port) {
 	}
 }
 
-void InstallExceptionHandler(BadAccessHandler badAccessHandler) {
+void InstallExceptionHandler(BadAccessHandler badAccessHandler, bool logStackTraceOnCrash) {
 	if (g_badAccessHandler) {
 		// The rest of the setup we don't need to do again.
 		g_badAccessHandler = badAccessHandler;
@@ -282,7 +336,7 @@ static void sigsegv_handler(int sig, siginfo_t* info, void* raw_context) {
 	}
 }
 
-void InstallExceptionHandler(BadAccessHandler badAccessHandler) {
+void InstallExceptionHandler(BadAccessHandler badAccessHandler, bool logStackTraceOnCrash) {
 	if (!badAccessHandler) {
 		return;
 	}
@@ -351,7 +405,7 @@ void UninstallExceptionHandler() {
 
 #else  // !MACHINE_CONTEXT_SUPPORTED
 
-void InstallExceptionHandler(BadAccessHandler badAccessHandler) {
+void InstallExceptionHandler(BadAccessHandler badAccessHandler, bool logStackTraceOnCrash) {
 	ERROR_LOG(Log::System, "Exception handler not implemented on this platform, can't install");
 }
 void UninstallExceptionHandler() { }

Common/ExceptionHandlerSetup.h

@@ -13,7 +13,11 @@
 // Ugh, might need to abstract this better.
 typedef bool (*BadAccessHandler)(uintptr_t address, void *context);
 
-void InstallExceptionHandler(BadAccessHandler accessHandler);
+// logStackTraceOnCrash: if true, log a best-effort stack trace (via dbghelp on Windows)
+// when a genuinely unhandled access violation is about to crash the process. Off by
+// default since it links dbghelp and walks the stack from inside the exception handler -
+// opt in only when you're chasing a native crash.
+void InstallExceptionHandler(BadAccessHandler accessHandler, bool logStackTraceOnCrash = false);
 
 // Implementation note: This must be a no-op if InstallExceptionHandler hasn't been called.
 void UninstallExceptionHandler();

Core/CmdLine.cpp

@@ -186,6 +186,7 @@ static const CommandLineParam g_autoParams[] = {
 	{POFF(memReadAction), CmdParamType::Enum, "memread", '\0', "Set the action for memory read exceptions", CmdLineMode::Both, g_ExceptionActionValues, ARRAY_SIZE(g_ExceptionActionValues)},
 	{POFF(memWriteAction), CmdParamType::Enum, "memwrite", '\0', "Set the action for memory write exceptions", CmdLineMode::Both, g_ExceptionActionValues, ARRAY_SIZE(g_ExceptionActionValues)},
 	{POFF(breakAction), CmdParamType::Enum, "break", '\0', "Set the action for break exceptions", CmdLineMode::Both, g_ExceptionActionValues, ARRAY_SIZE(g_ExceptionActionValues)},
+	{POFF(logNativeCrashes), CmdParamType::Bool, "log-native-crashes", '\0', "Log a native stack trace (Windows only) on an otherwise-unhandled crash", CmdLineMode::Both},
 	{POFF(verbose), CmdParamType::Bool, "verbose", '\0', "Enable verbose output", CmdLineMode::Both},
 
 	// TODO: At some point we should maybe simply expose all config settings to be set directly from the command line automatically?
@@ -498,6 +499,11 @@ void CommandLineOptions::ApplyToConfig() const {
 		g_Config.DoNotSaveSetting(&g_Config.iExceptionActionBreak);
 	}
 
+	if (logNativeCrashes.has_value()) {
+		g_Config.bLogNativeCrashStackTraces = logNativeCrashes.value();
+		g_Config.DoNotSaveSetting(&g_Config.bLogNativeCrashStackTraces);
+	}
+
 	// --vsh is applied by the caller (by setting their boot file name variable).
 
 	// Note: dpi is not applied here - it's platform-specific.

Core/CmdLine.h

@@ -59,6 +59,9 @@ struct CommandLineOptions {
 	std::optional<int> memWriteAction;
 	std::optional<int> breakAction;
 
+	// Log a native stack trace (Windows only) on an otherwise-unhandled access violation.
+	std::optional<bool> logNativeCrashes;
+
 	// SDL only: Option to force a specific OpenGL version (42="4.2",
 	// etc.; -1 means "try them all").
 	// Implemented as a workaround for https://github.com/hrydgard/ppsspp/issues/20687

Core/Config.h

@@ -218,6 +218,11 @@ public:
 	int iExceptionActionMemWrite;
 	int iExceptionActionBreak;
 
+	// If true, log a best-effort native stack trace (Windows only) when a genuinely
+	// unhandled access violation is about to crash the process. Diagnostic only, off by
+	// default - see --log-native-crashes in Core/CmdLine.cpp.
+	bool bLogNativeCrashStackTraces;
+
 	bool bFastMemory;
 	int iCpuCore;
 	bool bCheckForNewVersion;

Core/System.cpp

@@ -517,7 +517,7 @@ static bool CPU_Init(FileLoader *fileLoader, IdentifiedFileType type, std::strin
 		g_CoreParameter.gpuCore = GPUCORE_SOFTWARE;
 	}
 
-	InstallExceptionHandler(&Memory::HandleFault);
+	InstallExceptionHandler(&Memory::HandleFault, g_Config.bLogNativeCrashStackTraces);
 
 	return true;
 }