tweaks_howto.txt

How to tweak existing classes using ASM and JavaScript
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1. Note the class file you want to change.
2. Compile it in original form, reobfuscate, save that file (orig.class).
3. Make changes, preferably at the beginning or the end of the methods.
4. Compile the changed class file, reobfuscate, save (mod.class).
5. Run Asmifier4JS on both saved files:

java -cp . org.objectweb.asm.util.ASMifier4JS orig.class >orig.asm
java -cp . org.objectweb.asm.util.ASMifier4JS mod.class >mod.asm

6. Run a diff on the "asmified" files to see how bytecode is changed:

diff -U 100 orig.asm mod.asm >changes.diff

7. Note the changes and write JavaScript code that makes such changes.
   You'd want to insert bytecode at notable places that are unlikely to
   change: unique names, constants, beginning or the end of the code.
   Refer to the tweak_*.js files to see how patches should look like.