Hook individual objects #15
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| Class clazz = object_getClass(obj); | ||
| Class superclazz = class_getSuperclass(clazz); | ||
| do { | ||
| let superclassMethod = class_getInstanceMethod(superclazz, _cmd); | ||
| let sameMethods = class_getInstanceMethod(clazz, _cmd) == superclassMethod; | ||
| if (!sameMethods && !ITKMethodIsSuperTrampoline(superclassMethod)) { | ||
| break; | ||
| } | ||
| clazz = superclazz; | ||
| superclazz = class_getSuperclass(clazz); | ||
| }while (1); |
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This is not going to work. Let's consider the same situation as in the description above, but now Level3 and Level4 classes override the -sayHello method.
Also, there is no way to determine if Method uses our trampoline or not, since Method can contain user-defined IMP which can call our trampoline IMP.
Seems like the only correct and efficient way to implement this is to use vm_remap() and PC-relative addressing in the same way as this does original imp_implementationWithBlock.
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You're right - this is not a situation the current logic supports. It would be a fun challenge to try how complex a solution with real trampolines work. Happy to take PRs! I add this limitation to the readme for now.
This enables hooking on a per-object instance base, similar to https://github.com/steipete/Aspects.
The strategy here is:
This can be made fully reversible, we can unregister the dynamically created subclass; potentially also reuse. Since we - unlike Aspects - don't use
_objc_msgForward, no boxing happens, and this approach is fast + safe.I ran into a few Swift compiler crashers:
TODO:
_objc_msgSendSuper2_stretfor non-arm64