Avoid undefined behaviour after realloc()
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result and the old allocation to update pointers into the new allocation is undefined behaviour: the old pointers are no longer valid after realloc() according to the C standard.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 value_list 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
xev over SSH on a CHERI-RISC-V system. With these two
realloc changes, and xorg/proto/xorgproto!41 (merged)
I am able to succesfully run
xev compiled for CHERI-RISC-V.
Signed-off-by: Alex Richardson Alexander.Richardson@cl.cam.ac.uk