Yes, absolutely! In the case of Arm, it would need to be a pure macro (i.e. no external __defer function) since ARM ABI uses a register to store the return addr

Yes, absolutely! In the case of Arm, it would need to be a pure macro (i.e. no external __defer function) since ARM ABI uses a register to store the return address. Then the unwind code would need to save the return registers x0 to x7 each time it calls free() or whatever function is being deferred. I'd write it for you, but I don't use ARM.