Question

I am working with IJVM and trying to use the GOTO instruction using a local variable in place of a static offset (or label). It won’t work. I suppose it is simply treating the variable name as a label and trying to branch to it, but no such label exists. Is there any way I can force it to read the contents of the variable (which contains an offset), or some other solution?

Thanks in advance.

Answer 1

For security reasons, JVM bytecode doesn’t let you jump to arbitrary instructions based on the contents of a variable. This restriction makes it possible for the JVM to verify various security properties of the bytecode by statically enumerating all control paths through a particular method. If you were able to jump anywhere, the static analyzer couldn’t prove that all necessary program invariants held.

If you do need to jump to an arbitrary index, consider looking into the tableswitch or lookupswitch instructions, which would let you enumerate possible destinations in advance. It’s not exactly what you’re looking for, but to the best of my knowledge the sort of arbitrary jump you’re trying to make isn’t possible in JVM bytecode.

Hope this helps!