I cannot run run-as (or ndk-gdb) for the Galaxy S4 running Jellybean 4.2.2.
~ $ adb shell shell@android:/ $ run-as a.b.c ls run-as: Package \'a.b.c\' is un
There is a known issue with the latest version of Nexus 7. Simply downgrade to 4.2 (or get 4.3 without the mini-update) and you should be fine. There's a discussion here about it:
http://code.google.com/p/android/issues/detail?id=58373