Statically determing unused code path in Android apk [closed]

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I want to statically determine unused code path in Android apk i.e. I want to find out all paths in .dex file that my code will never reach. What are the possible ways to do so ?

Answer 1

Generally speaking, the javac compiler doesn't generate dead code. If something can be statically determined to be unreachable, the compile will fail. For example:

void foo() {
    throw new RuntimeException();

    doStuff();
}

This results in an "unreachable statement" failure. You can "hint" to the compiler that you want to do this anyway:

void foo() {
    if (true) throw new RuntimeException();

    doStuff();
}

However, the compiler still knows that the call to doStuff() is unreachable, and discards it.

If you did manage to get dead code into a DEX file, the bytecode verifier will optionally tell you about it -- look for DEAD_CODE_SCAN in the verifier source.

All of that is for dead code inside a method. For identifying whole methods that are never actually called, you can use ProGuard (which is an optional but officially supported part of Android app builds). This can false-positive and remove methods that are never called directly but may be called through reflection, so manual overrides are sometimes required.