I am looking to do an experiment where in I can reserve ARM CPU register, say X25 to be not used by the compiler. Looking at the armclang reference document that says,
Syntax -ffixed-rN
Parameters N specifies the register number, which can be any number from 5 to 11. This enables you to reserve core registers R5 to R11.
Restrictions This feature is only available for AArch32 state.
Does that mean I cannot use this option in 64-bit architecture ? In that case how can i reserve a particular CPU register with armclang compiler ?