This allows us to avoid needing to worry about manipulating stack frames
in individual transformers, which adds lots of complexity. It's much
easier to just make ASM generate them for us.
Signed-off-by: Graham <gpe@openrs2.dev>
Fernflower was previously placing constructors in the middle of instance
methods. They look much nicer at the top.
This commit also ensures static methods appear before instance methods.
The client scrambles static fields and methods - moving each to a
random class where it does not logically belong.
This transformer moves all static methods to a new set of empty classes.
The intention is that the human refactoring the deobfuscated client can
move the static methods around with an IDE to classes where it makes
sense.
In theory we could use heuristics to move some methods around - e.g.
ideas I have include:
* If the method takes no arguments, move it to the same class as its
return type.
* If it's a void method that takes one argument, move it to the same
class as its single argument.
* Group related methods together based on where they are called.
However, some of the heuristics are probably fairly complicated to
implement. Furthermore, as they are heuristics, they will make mistakes.
In the naive approach, the Static* classes generated by this transformer
effectively act as a queue of methods that a human has yet to move to an
appropriate class. If the Static* classes are ever emptied after
refactoring, then we will know that all static methods have been moved
to an appropriate class.
We wouldn't be able to guarantee this if some methods were moved to
Class* classes with heuristics. The heuristics would also be fairly
complicated to implement. Therefore, the transformer does not use
heuristics.
Field scrambling support will be included in a future commit.
The obfuscator (or compiler, potentially?) converts INVOKEVIRTUAL
instructions to INVOKESPECIAL in the following circumstances:
* The owner of the method is the same as the class containing the
INVOKE instruction.
* The owner's ACC_FINAL flag is set.
When those two conditions are met, and when ACC_SUPER is set on the
owner (which is always true in the RuneScape client, and the flag is
ignored in modern JVMs), then INVOKESPECIAL and INVOKEVIRTUAL are
equivalent.
This has not caused problems until now. However, the future static
scrambling transformer will break the first condition in some cases, as
it moves methods between classes.
This transformer reverses the obfuscation, such that INVOKEVIRTUAL is
used again. INVOKEVIRTUAL instructions may be moved between classes
without complication.
In Java 1.4 and earlier, the compiler creates a synthetic method for
invoking Class.forName() and a static field for caching the Class<?>
instance.
This will not interact well with the static scrambling transformer. The
obfuscator strips some synthetic flags. Furthermore, the field and
method need to be moved together with the code that uses them for
decompilers like Fernflower to recognise them and convert them back to
class literals.
If Fernflower misses one, the decompiled Class.forName() helper does not
compile cleanly (as the bytecode is missing a CHECKCAST).
Rather than complicating the future static scrambling transformer, it's
easier to convert these to use LDC and upgrade the .class file version
to Java 5.
Graham