earlyprintk

This is the information I have.

http://developer.android.com/guide/developing/debugging/index.html
http://developer.android.com/guide/developing/tools/logcat.html
and one important point logcat can provide different log sources
http://developer.android.com/guide/developing/debugging/debugging-log.html

some links about logcat and log related
Android Zygote Startup - eLinux.orgZygote
http://elinux.org/Android_Zygote_Startup
http://elinux.org/Android_Logging_System

the next comment i found in main_runtime.cpp not sure where it could go, init.rc or other system file you can read next link for Android boot sequence, but all must be covered by logwrappers to use in init.rc described in previous link.

I tried to find this file in JB or ICS but it is not there only up to GB.

/mydroid/frameworks/base/cmds/runtime/main_runtime.cpp

static void usage(const char* argv0)
{
    fprintf(stderr,
        "Usage: runtime [-g gamma] [-l logfile] [-n] [-s]\n"
        "               [-j app-component] [-v app-verb] [-d app-data]\n"
        "\n"
        "-l: File to send log messages to\n"
        "-n: Don't print to stdout/stderr\n"
        "-s: Force single-process mode\n"
        "-j: Custom home app component name\n"
        "-v: Custom home app intent verb\n"
        "-d: Custom home app intent data\n"
    );
    exit(1);
}

Just to complement my previous post.

You can use loggers or logcat to send the output of a binary to logcat, it is needed to run logcat from inside init.rc.

One thing about init files is that they have debug logs but they are disabled, it is needed to open the file and enable the debug flag.

for example,

/GB/mydroid/frameworks/base/services/jni/com_android_server_InputManager.cpp

to enable debug it can be selected at the beginning of first file and recompiling, uncomment it or set to 1, try using logcat *:* to enable all options
there are other options

#define LOG_TAG "InputManager-JNI"
//#define LOG_NDEBUG 0
// Log debug messages about InputReaderPolicy
#define DEBUG_INPUT_READER_POLICY 0
// Log debug messages about InputDispatcherPolicy
#define DEBUG_INPUT_DISPATCHER_POLICY 0