AntiClassDump

AntiClassDump is a pass designed to defeat class-dump for targets using Modern ObjC Runtime. In short, it cleans up traces of ObjC classes in IR so neither ObjC runtime or class-dump to extract them. Then it generates code to dynamically create and register classes.

By design acd uses a two-stage pattern to solve the issue of class dependency calculation while not forcing LTO. Traditionally LTO is enforced for the pass to calculate class dependency correctly

Stage 1(Implemented)

Most of the ObjC structs are left intact, the exception being method lists.Only +initialize is kept (Or created from scratch if there isn't one). And +initialize is where all Stage1 magic take place. Note in order to save ourselves from the trouble of deallocating and re-allocating class pairs, we only handle methods at stage 1.

Stage 2(Unimplemented)

Stage 2 takes place at LTO stage where we can, and did, calculate the dependency graph. During this stage existing ObjC structures are wiped out completely, we create completely new initialize routines from scratch and use llvm.global_ctors to mark our initializer as constructors for the backend/linker to handle

Options

-enable-acdobf

Enable AntiClassDump

acd-use-initialize

By default AntiClassDump used +initialize as insert point, adding this flag to false uses +load . This is mainly for adjusting bootstrapping sequence. For example there is a binary linking to a framework. Both obfuscated with ACD. If you send message to class in the framework in binary's +load, ObjC runtime will throw an exception since framework's +load is not called yet. In this case you should change framework's flags to use +initialize instead of +load

Issues

Various System Libraries, for example storyboard depends on methods/setters/getters, which is wiped by Anti-ClassDump, try per file CFLAGS instead of global CFLAGS, and turn off ACD for this kind of classes