Implement --debugger option to improve UX when debugging crashes (#13157)

src/main.cpp

@@ -102,6 +102,7 @@ static void list_game_ids();
 static void list_worlds(bool print_name, bool print_path);
 static bool setup_log_params(const Settings &cmd_args);
 static bool create_userdata_path();
+static bool use_debugger(int argc, char *argv[]);
 static bool init_common(const Settings &cmd_args, int argc, char *argv[]);
 static void uninit_common();
 static void startup_message();
@@ -162,6 +163,11 @@ int main(int argc, char *argv[])
 	if (!setup_log_params(cmd_args))
 		return 1;
 
+	if (cmd_args.getFlag("debugger")) {
+		if (!use_debugger(argc, argv))
+			warningstream << "Continuing without debugger" << std::endl;
+	}
+
 	porting::signal_handler_init();
 
 #ifdef __ANDROID__
@@ -341,6 +347,8 @@ static void set_allowed_options(OptionList *allowed_options)
 			_("Print even more information to console"))));
 	allowed_options->insert(std::make_pair("trace", ValueSpec(VALUETYPE_FLAG,
 			_("Print enormous amounts of information to log and console"))));
+	allowed_options->insert(std::make_pair("debugger", ValueSpec(VALUETYPE_FLAG,
+			_("Try to automatically attach a debugger before starting (convenience option)"))));
 	allowed_options->insert(std::make_pair("logfile", ValueSpec(VALUETYPE_STRING,
 			_("Set logfile path ('' = no logging)"))));
 	allowed_options->insert(std::make_pair("gameid", ValueSpec(VALUETYPE_STRING,
@@ -535,6 +543,126 @@ static bool create_userdata_path()
 	return success;
 }
 
+namespace {
+	std::string findProgram(const char *name)
+	{
+		char *path_c = getenv("PATH");
+		if (!path_c)
+			return "";
+		std::istringstream iss(path_c);
+		std::string checkpath;
+		while (!iss.eof()) {
+			std::getline(iss, checkpath, PATH_DELIM[0]);
+			if (!checkpath.empty() && checkpath.back() != DIR_DELIM_CHAR)
+				checkpath.push_back(DIR_DELIM_CHAR);
+			checkpath.append(name);
+			if (fs::IsExecutable(checkpath))
+				return checkpath;
+		}
+		return "";
+	}
+
+#ifdef _WIN32
+	const char *debuggerNames[] = {"gdb.exe", "lldb.exe"};
+#else
+	const char *debuggerNames[] = {"gdb", "lldb"};
+#endif
+	template <class T>
+	void getDebuggerArgs(T &out, int i) {
+		if (i == 0) {
+			for (auto s : {"-q", "--batch", "-iex", "set confirm off",
+				"-ex", "run", "-ex", "bt", "--args"})
+				out.push_back(s);
+		} else if (i == 1) {
+			for (auto s : {"-Q", "-b", "-o", "run", "-k", "bt\nq", "--"})
+				out.push_back(s);
+		}
+	}
+}
+
+static bool use_debugger(int argc, char *argv[])
+{
+#if defined(__ANDROID__)
+	return false;
+#else
+#ifdef _WIN32
+	if (IsDebuggerPresent()) {
+		warningstream << "Process is already being debugged." << std::endl;
+		return false;
+	}
+#endif
+
+	char exec_path[1024];
+	if (!porting::getCurrentExecPath(exec_path, sizeof(exec_path)))
+		return false;
+
+	int debugger = -1;
+	std::string debugger_path;
+	for (u32 i = 0; i < ARRLEN(debuggerNames); i++) {
+		debugger_path = findProgram(debuggerNames[i]);
+		if (!debugger_path.empty()) {
+			debugger = i;
+			break;
+		}
+	}
+	if (debugger == -1) {
+		warningstream << "Couldn't find a debugger to use. Try installing gdb or lldb." << std::endl;
+		return false;
+	}
+
+	// Try to be helpful
+#ifdef NDEBUG
+	if (strcmp(BUILD_TYPE, "RelWithDebInfo") != 0) {
+		warningstream << "It looks like your " PROJECT_NAME_C " executable was built without "
+			"debug symbols (BUILD_TYPE=" BUILD_TYPE "), so you won't get useful backtraces."
+			<< std::endl;
+	}
+#endif
+
+	std::vector<const char*> new_args;
+	new_args.push_back(debugger_path.c_str());
+	getDebuggerArgs(new_args, debugger);
+	// Copy the existing arguments
+	new_args.push_back(exec_path);
+	for (int i = 1; i < argc; i++) {
+		if (!strcmp(argv[i], "--debugger"))
+			continue;
+		new_args.push_back(argv[i]);
+	}
+	new_args.push_back(nullptr);
+
+#ifdef _WIN32
+	// Special treatment for Windows
+	std::string cmdline;
+	for (int i = 1; new_args[i]; i++) {
+		if (i > 1)
+			cmdline += ' ';
+		cmdline += porting::QuoteArgv(new_args[i]);
+	}
+
+	STARTUPINFO startup_info = {};
+	PROCESS_INFORMATION process_info = {};
+	bool ok = CreateProcess(new_args[0], cmdline.empty() ? nullptr : &cmdline[0],
+		nullptr, nullptr, false, CREATE_UNICODE_ENVIRONMENT,
+		nullptr, nullptr, &startup_info, &process_info);
+	if (!ok) {
+		warningstream << "CreateProcess: " << GetLastError() << std::endl;
+		return false;
+	}
+	DWORD exitcode = 0;
+	WaitForSingleObject(process_info.hProcess, INFINITE);
+	GetExitCodeProcess(process_info.hProcess, &exitcode);
+	exit(exitcode);
+	// not reached
+#else
+	errno = 0;
+	execv(new_args[0], const_cast<char**>(new_args.data()));
+	warningstream << "execv: " << strerror(errno) << std::endl;
+	return false;
+#endif
+#endif
+}
+
 static bool init_common(const Settings &cmd_args, int argc, char *argv[])
 {
 	startup_message();