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

6 files changed, 191 insertions, 11 deletions

diff --git a/src/filesys.cpp b/src/filesys.cpp
index 7edb60bcd..d610c2311 100644
--- a/src/filesys.cpp
+++ b/src/filesys.cpp
@@ -127,6 +127,12 @@ bool IsDir(const std::string &path)
 			(attr & FILE_ATTRIBUTE_DIRECTORY));
 }
 
+bool IsExecutable(const std::string &path)
+{
+	DWORD type;
+	return GetBinaryType(path.c_str(), &type) != 0;
+}
+
 bool IsDirDelimiter(char c)
 {
 	return c == '/' || c == '\\';
@@ -309,6 +315,11 @@ bool IsDir(const std::string &path)
 	return ((statbuf.st_mode & S_IFDIR) == S_IFDIR);
 }
 
+bool IsExecutable(const std::string &path)
+{
+	return access(path.c_str(), X_OK) == 0;
+}
+
 bool IsDirDelimiter(char c)
 {
 	return c == '/';
diff --git a/src/filesys.h b/src/filesys.h
index a26fe28d6..fa9ddcaa8 100644
--- a/src/filesys.h
+++ b/src/filesys.h
@@ -60,6 +60,8 @@ bool IsPathAbsolute(const std::string &path);
 
 bool IsDir(const std::string &path);
 
+bool IsExecutable(const std::string &path);
+
 inline bool IsFile(const std::string &path)
 {
 	return PathExists(path) && !IsDir(path);
diff --git a/src/gettext.cpp b/src/gettext.cpp
index de042cf35..f56738d98 100644
--- a/src/gettext.cpp
+++ b/src/gettext.cpp
@@ -149,28 +149,25 @@ void init_gettext(const char *path, const std::string &configured_language,
 				"Restarting " PROJECT_NAME_C " in a new environment!" << std::endl;
 
 			std::string parameters;
-
-			for (unsigned int i = 1; i < argc; i++) {
-				if (!parameters.empty())
+			for (int i = 1; i < argc; i++) {
+				if (i > 1)
 					parameters += ' ';
-
-				parameters += argv[i];
+				parameters += porting::QuoteArgv(argv[i]);
 			}
 
-			const char *ptr_parameters = NULL;
-
+			char *ptr_parameters = nullptr;
 			if (!parameters.empty())
-				ptr_parameters = parameters.c_str();
+				ptr_parameters = &parameters[0];
 
 			// Allow calling without an extension
 			std::string app_name = argv[0];
 			if (app_name.compare(app_name.size() - 4, 4, ".exe") != 0)
 				app_name += ".exe";
 
-			STARTUPINFO startup_info = {0};
-			PROCESS_INFORMATION process_info = {0};
+			STARTUPINFO startup_info = {};
+			PROCESS_INFORMATION process_info = {};
 
-			bool success = CreateProcess(app_name.c_str(), (char *)ptr_parameters,
+			bool success = CreateProcess(app_name.c_str(), ptr_parameters,
 				NULL, NULL, false, DETACHED_PROCESS | CREATE_UNICODE_ENVIRONMENT,
 				NULL, NULL, &startup_info, &process_info);
 
diff --git a/src/main.cpp b/src/main.cpp
index 35dcb708b..ec805f5d3 100644
--- a/src/main.cpp
+++ b/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();
diff --git a/src/porting.cpp b/src/porting.cpp
index 475292b97..629f00c37 100644
--- a/src/porting.cpp
+++ b/src/porting.cpp
@@ -729,6 +729,38 @@ void attachOrCreateConsole()
 #endif
 }
 
+#ifdef _WIN32
+std::string QuoteArgv(const std::string &arg)
+{
+	// Quoting rules on Windows are batshit insane, can differ between applications
+	// and there isn't even a stdlib function to deal with it.
+	// Ref: https://learn.microsoft.com/archive/blogs/twistylittlepassagesallalike/everyone-quotes-command-line-arguments-the-wrong-way
+	if (!arg.empty() && arg.find_first_of(" \t\n\v\"") == std::string::npos)
+		return arg;
+
+	std::string ret;
+	ret.reserve(arg.size()+2);
+	ret.push_back('"');
+	for (auto it = arg.begin(); it != arg.end(); ++it) {
+		u32 back = 0;
+		while (it != arg.end() && *it == '\\')
+			++back, ++it;
+
+		if (it == arg.end()) {
+			ret.append(2 * back, '\\');
+			break;
+		} else if (*it == '"') {
+			ret.append(2 * back + 1, '\\');
+		} else {
+			ret.append(back, '\\');
+		}
+		ret.push_back(*it);
+	}
+	ret.push_back('"');
+	return ret;
+}
+#endif
+
 int mt_snprintf(char *buf, const size_t buf_size, const char *fmt, ...)
 {
 	// https://msdn.microsoft.com/en-us/library/bt7tawza.aspx
diff --git a/src/porting.h b/src/porting.h
index 93932e1d9..cc23e3c62 100644
--- a/src/porting.h
+++ b/src/porting.h
@@ -156,6 +156,11 @@ extern std::string path_locale;
 extern std::string path_cache;
 
 /*
+	Gets the path of our executable.
+*/
+bool getCurrentExecPath(char *buf, size_t len);
+
+/*
 	Get full path of stuff in data directory.
 	Example: "stone.png" -> "../data/stone.png"
 */
@@ -330,6 +335,11 @@ bool secure_rand_fill_buf(void *buf, size_t len);
 // This attaches to the parents process console, or creates a new one if it doesnt exist.
 void attachOrCreateConsole();
 
+#ifdef _WIN32
+// Quotes an argument for use in a CreateProcess() commandline (not cmd.exe!!)
+std::string QuoteArgv(const std::string &arg);
+#endif
+
 int mt_snprintf(char *buf, const size_t buf_size, const char *fmt, ...);
 
 /**