principle of QEMU CPU emulation
Please see this file for the C-level modelling of the state of an ARM CPU as done by QEMU.
It's pretty straight-forward, and (of course) as you suspect the registers (and all other state) are modelled as C variables.
The core structure begins:
typedef struct CPUARMState { /* Regs for current mode. */ uint32_t regs[16]; /* Frequently accessed CPSR bits are stored separately for efficiency. This contains all the other bits. Use cpsr_{read,write} to access the whole CPSR. */ uint32_t uncached_cpsr; uint32_t spsr;