Merge "init: add sigstop option for debugging services from their start" (b4187911) · Commits · e / os / android_system_core

init/README.md

+40 −20

Original line number	Diff line number	Diff line
		@@ -282,6 +282,10 @@ runs the service.
		"shutdown critical" will be killed. When the service tagged with "shutdown critical"
		is not running when shut down starts, it will be started.

		`sigstop`
		> Send SIGSTOP to the service immediately before exec is called. This is intended for debugging.
		See the below section on debugging for how this can be used.

		`socket <name> <type> <perm> [ <user> [ <group> [ <seclabel> ] ] ]`
		> Create a unix domain socket named /dev/socket/_name_ and pass its fd to the
		launched process. _type_ must be "dgram", "stream" or "seqpacket". User and
		@@ -708,23 +712,39 @@ affected.

		Debugging init
		--------------
		By default, programs executed by init will drop stdout and stderr into
		/dev/null. To help with debugging, you can execute your program via the
		Android program logwrapper. This will redirect stdout/stderr into the
		Android logging system (accessed via logcat).

		For example
		service akmd /system/bin/logwrapper /sbin/akmd

		For quicker turnaround when working on init itself, use:

		mm -j &&
		m ramdisk-nodeps &&
		m bootimage-nodeps &&
		adb reboot bootloader &&
		fastboot boot $ANDROID_PRODUCT_OUT/boot.img

		Alternatively, use the emulator:

		emulator -partition-size 1024 \
		-verbose -show-kernel -no-window
		Launching init services without init is not recommended as init sets up a significant amount of
		environment (user, groups, security label, capabilities, etc) that is hard to replicate manually.

		If it is required to debug a service from its very start, the `sigstop` service option is added.
		This option will send SIGSTOP to a service immediately before calling exec. This gives a window
		where developers can attach a debugger, strace, etc before continuing the service with SIGCONT.

		This flag can also be dynamically controled via the ctl.sigstop_on and ctl.sigstop_off properties.

		Below is an example of dynamically debugging logd via the above:

		stop logd
		setprop ctl.sigstop_on logd
		start logd
		ps -e \| grep logd
		> logd 4343 1 18156 1684 do_signal_stop 538280 T init
		gdbclient.py -p 4343
		b main
		c
		c
		c
		> Breakpoint 1, main (argc=1, argv=0x7ff8c9a488) at system/core/logd/main.cpp:427

		Below is an example of doing the same but with strace

		stop logd
		setprop ctl.sigstop_on logd
		start logd
		ps -e \| grep logd
		> logd 4343 1 18156 1684 do_signal_stop 538280 T init
		strace -p 4343

		(From a different shell)
		kill -SIGCONT 4343

		> strace runs

init/init.cpp

+4 −0

Original line number	Diff line number	Diff line
		@@ -238,6 +238,10 @@ struct ControlMessageFunction {
		static const std::map<std::string, ControlMessageFunction>& get_control_message_map() {
		// clang-format off
		static const std::map<std::string, ControlMessageFunction> control_message_functions = {
		{"sigstop_on", {ControlTarget::SERVICE,
		[](auto* service) { service->set_sigstop(true); return Success(); }}},
		{"sigstop_off", {ControlTarget::SERVICE,
		[](auto* service) { service->set_sigstop(false); return Success(); }}},
		{"start", {ControlTarget::SERVICE, DoControlStart}},
		{"stop", {ControlTarget::SERVICE, DoControlStop}},
		{"restart", {ControlTarget::SERVICE, DoControlRestart}},

init/service.cpp

+12 −2

Original line number	Diff line number	Diff line
		@@ -155,7 +155,7 @@ static void SetUpPidNamespace(const std::string& service_name) {
		}
		}

		static bool ExpandArgsAndExecv(const std::vector<std::string>& args) {
		static bool ExpandArgsAndExecv(const std::vector<std::string>& args, bool sigstop) {
		std::vector<std::string> expanded_args;
		std::vector<char*> c_strings;

		@@ -169,6 +169,10 @@ static bool ExpandArgsAndExecv(const std::vector<std::string>& args) {
		}
		c_strings.push_back(nullptr);

		if (sigstop) {
		kill(getpid(), SIGSTOP);
		}

		return execv(c_strings[0], c_strings.data()) == 0;
		}

		@@ -582,6 +586,11 @@ Result<Success> Service::ParseSeclabel(const std::vector<std::string>& args) {
		return Success();
		}

		Result<Success> Service::ParseSigstop(const std::vector<std::string>& args) {
		sigstop_ = true;
		return Success();
		}

		Result<Success> Service::ParseSetenv(const std::vector<std::string>& args) {
		environment_vars_.emplace_back(args[1], args[2]);
		return Success();
		@@ -704,6 +713,7 @@ const Service::OptionParserMap::Map& Service::OptionParserMap::map() const {
		{"seclabel", {1, 1, &Service::ParseSeclabel}},
		{"setenv", {2, 2, &Service::ParseSetenv}},
		{"shutdown", {1, 1, &Service::ParseShutdown}},
		{"sigstop", {0, 0, &Service::ParseSigstop}},
		{"socket", {3, 6, &Service::ParseSocket}},
		{"user", {1, 1, &Service::ParseUser}},
		{"writepid", {1, kMax, &Service::ParseWritepid}},
		@@ -862,7 +872,7 @@ Result<Success> Service::Start() {
		// priority. Aborts on failure.
		SetProcessAttributes();

		if (!ExpandArgsAndExecv(args_)) {
		if (!ExpandArgsAndExecv(args_, sigstop_)) {
		PLOG(ERROR) << "cannot execve('" << args_[0] << "')";
		}

init/service.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -118,6 +118,7 @@ class Service {
		bool is_override() const { return override_; }
		bool process_cgroup_empty() const { return process_cgroup_empty_; }
		unsigned long start_order() const { return start_order_; }
		void set_sigstop(bool value) { sigstop_ = value; }
		const std::vector<std::string>& args() const { return args_; }

		private:
		@@ -153,6 +154,7 @@ class Service {
		Result<Success> ParseSeclabel(const std::vector<std::string>& args);
		Result<Success> ParseSetenv(const std::vector<std::string>& args);
		Result<Success> ParseShutdown(const std::vector<std::string>& args);
		Result<Success> ParseSigstop(const std::vector<std::string>& args);
		Result<Success> ParseSocket(const std::vector<std::string>& args);
		Result<Success> ParseFile(const std::vector<std::string>& args);
		Result<Success> ParseUser(const std::vector<std::string>& args);
		@@ -213,6 +215,8 @@ class Service {

		std::vector<std::pair<int, rlimit>> rlimits_;

		bool sigstop_ = false;

		std::vector<std::string> args_;

		std::vector<std::function<void(const siginfo_t& siginfo)>> reap_callbacks_;