[monodroid] Add debug.mono.log=debugger-log-level=LEVEL option (#3969)

The mono debugger infrastructure code supports a `loglevel` option,
which the mono debugger team would like to set.

In theory we have code to allow setting set it: the `debug.mono.extra`
system property can contain a `loglevel=LEVEL` option, which is
parsed by `mono_runtime_init()`/`parse_runtime_args()` when
constructing the options for use with `mono_jit_parse_options()`.

In practice, we don't: [all codepaths][0] which set `debug.mono.extra`
always hardcode `loglevel=0`, with no way to override it.

To allow the mono debugger team to *actually* set the `loglevel`
value, add a new `debugger-log-level=LEVEL` option for use with the
`debug.mono.log` system property:

	adb shell setprop debug.mono.log debugger-log-level=10

The `debug.mono.log` system property is comma-separated, so it can be
used with other options as well:

	adb shell setprop debug.mono.log timing,gref,debugger-log-level=10

The `LEVEL` value is a positive 32-bit signed integer or `0`.  This
option will take precedence when the level is set in both the
`debug.mono.extra` and `debug.mono.log` system properties.

[0]: https://github.com/xamarin/androidtools/blob/master/Xamarin.AndroidTools/Debugging/DebuggingExtensions.cs#L92-L102

src/monodroid/jni/debug.cc

@@ -134,6 +134,29 @@ Debug::load_profiler_from_handle (void *dso_handle, const char *desc, const char
 }
 
 #if defined (DEBUG) && !defined (WINDOWS)
+void
+Debug::set_debugger_log_level (const char *level)
+{
+	if (level == nullptr || *level == '\0') {
+		got_debugger_log_level = false;
+		return;
+	}
+
+	unsigned long v = strtoul (level, nullptr, 0);
+	if (v == ULONG_MAX && errno == ERANGE) {
+		log_error (LOG_DEFAULT, "Invalid debugger log level value '%s', expecting a positive integer or zero", level);
+		return;
+	}
+
+	if (v > INT_MAX) {
+		log_warn (LOG_DEFAULT, "Debugger log level value is higher than the maximum of %u, resetting to the maximum value.", INT_MAX);
+		v = INT_MAX;
+	}
+
+	got_debugger_log_level = true;
+	debugger_log_level = static_cast<int>(v);
+}
+
 inline void
 Debug::parse_options (char *options, ConnOptions *opts)
 {

src/monodroid/jni/debug.hh

@@ -58,6 +58,17 @@ namespace xamarin::android
 	public:
 		bool         enable_soft_breakpoints ();
 		void         start_debugging_and_profiling ();
+		void         set_debugger_log_level (const char *level);
+
+		bool         have_debugger_log_level () const
+		{
+			return got_debugger_log_level;
+		}
+
+		int          get_debugger_log_level () const
+		{
+			return debugger_log_level;
+		}
 
 	private:
 		DebuggerConnectionStatus start_connection (char *options);
@@ -67,6 +78,7 @@ namespace xamarin::android
 		bool         process_cmd (int fd, char *cmd);
 		void         start_debugging ();
 		void         start_profiling ();
+
 		friend void* conn_thread (void *arg);
 
 	private:
@@ -82,6 +94,8 @@ namespace xamarin::android
 		bool             config_timedout;
 		timeval          wait_tv;
 		timespec         wait_ts;
+		bool             got_debugger_log_level = false;
+		int              debugger_log_level = 0;
 #endif
 	};
 }

src/monodroid/jni/logger.cc

@@ -190,11 +190,14 @@ init_logging_categories ()
 		} else if (!strncmp (arg, "lref-", 5)) {
 			log_categories  |= LOG_LREF;
 			light_lref       = 1;
-		}
-
-		if (!strncmp (arg, "timing=bare", 11)) {
+		} else if (!strncmp (arg, "timing=bare", 11)) {
 			log_timing_categories |= LOG_TIMING_BARE;
 		}
+#if !defined (WINDOWS) && defined (DEBUG)
+		else if (!strncmp (arg, "debugger-log-level=", 19)) {
+			debug.set_debugger_log_level (arg + 19);
+		}
+#endif
 	}
 
 	utils.monodroid_strfreev (args);

src/monodroid/jni/monodroid-glue.cc

@@ -623,9 +623,15 @@ MonodroidRuntime::mono_runtime_init (char *runtime_args)
 	} else if (options.debug && cur_time <= options.timeout_time) {
 		embeddedAssemblies.set_register_debug_symbols (true);
 
+		int loglevel;
+		if (debug.have_debugger_log_level ())
+			loglevel = debug.get_debugger_log_level ();
+		else
+			loglevel = options.loglevel;
+
 		char *debug_arg = utils.monodroid_strdup_printf (
 			"--debugger-agent=transport=dt_socket,loglevel=%d,address=%s:%d,%sembedding=1",
-			options.loglevel,
+			loglevel,
 			options.host,
 			options.sdb_port,
 			options.server ? "server=y," : ""