init: add sigstop option for debugging services from their start
Test: the examples in README.md
Change-Id: Idb528ea4017f8f4ce62911928c040f4bc558d196
diff --git a/init/README.md b/init/README.md
index 59ddd77..b14521c 100644
--- a/init/README.md
+++ b/init/README.md
@@ -282,6 +282,10 @@
"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 @@
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).
+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.
-For example
-service akmd /system/bin/logwrapper /sbin/akmd
+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.
-For quicker turnaround when working on init itself, use:
+This flag can also be dynamically controled via the ctl.sigstop_on and ctl.sigstop_off properties.
- mm -j &&
- m ramdisk-nodeps &&
- m bootimage-nodeps &&
- adb reboot bootloader &&
- fastboot boot $ANDROID_PRODUCT_OUT/boot.img
+Below is an example of dynamically debugging logd via the above:
-Alternatively, use the emulator:
+ 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
- emulator -partition-size 1024 \
- -verbose -show-kernel -no-window
+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
diff --git a/init/init.cpp b/init/init.cpp
index 2f3b28a..0e019b0 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -238,6 +238,10 @@
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}},
diff --git a/init/service.cpp b/init/service.cpp
index 694e5e7..0227161 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -155,7 +155,7 @@
}
}
-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 @@
}
c_strings.push_back(nullptr);
+ if (sigstop) {
+ kill(getpid(), SIGSTOP);
+ }
+
return execv(c_strings[0], c_strings.data()) == 0;
}
@@ -578,6 +582,11 @@
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();
@@ -700,6 +709,7 @@
{"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}},
@@ -858,7 +868,7 @@
// priority. Aborts on failure.
SetProcessAttributes();
- if (!ExpandArgsAndExecv(args_)) {
+ if (!ExpandArgsAndExecv(args_, sigstop_)) {
PLOG(ERROR) << "cannot execve('" << args_[0] << "')";
}
diff --git a/init/service.h b/init/service.h
index d46a413..9b916c8 100644
--- a/init/service.h
+++ b/init/service.h
@@ -114,6 +114,7 @@
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:
@@ -149,6 +150,7 @@
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);
@@ -209,6 +211,8 @@
std::vector<std::pair<int, rlimit>> rlimits_;
+ bool sigstop_ = false;
+
std::vector<std::string> args_;
};
