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Adding the offset between the realloc result and the old allocation to update pointers into the new allocation is undefined behaviour: the old pointers are no longer valid after realloc() according to the C standard. While this works on almost all architectures and compilers, it causes problems on architectures that track pointer bounds (e.g. CHERI or Arm's Morello): the DevPrivateKey pointers will still have the bounds of the previous allocation and therefore any dereference will result in a run-time trap. I found this due to a crash (dereferencing an invalid capability) while trying to run `XVnc` on a CHERI-RISC-V system. With this commit I can successfully connect to the XVnc instance running inside a QEMU with a VNC viewer on my host. This also changes the check whether the allocation was moved to use uintptr_t instead of a pointer since according to the C standard: "The value of a pointer becomes indeterminate when the object it points to (or just past) reaches the end of its lifetime." Casting to an integer type avoids this undefined behaviour. Signed-off-by: Alex Richardson <Alexander.Richardson@cl.cam.ac.uk>