如何在Android上使用GDB运行Dalvik可执行文件？

Question

I want to debug an application on Android with GDB, I can hook on it with gdb and the process number but I want to see what it does from the start.

Would there be any way to do that?

Answer 1

On a rooted device or emulator you might be able to attach gdb to zygote and put a breakpoint right where the newly forked process is about to assume the identity of the application being launched.

It would probably be easiest if you modified zygote to wait for the debugger to attach. I believe there's something like this in the Jdwp debugging system that can get you into the Java debugger early in the startup of that code, but I don't know of something comparable for gdb already built in. Though I suppose you could get it waiting for jdwp, and attach gdb before you attach (and then detach) the java debugger.

Update: I tried this, by attaching to zygote with gdb and modifying a single word of code that will be executed early on by the child to go into an infinite loop, then detaching from zygote. I figured I would gdb the new child as soon as it shows up in 'ps' and restore it so that it can continue. The problem is that the child is being killed (presumably for being unresponsive) faster than I can get all the commands entered. So it would have to be done by a program. And there may not be that much you can see early on without stopping and getting it killed - I mean you could presumably get an strace in there, but what do you hope to learn that you can't learn from reading the source?

Answer 2

OMAPpedia's Android Debugging page has a good overview of using gdbclient.

gdbclient <executable name> <port number> <task name>

• executable name: file name in system/bin dir
• port number: default is :5039 (need the colon before the number)
• task name: obtained by running "ps" on the target. GDB uses it to identify the PID internally.

You may need to set up a port forward with adb first, like so:

adb forward tcp:5039 tcp:5039