principle of QEMU CPU emulation

Question

In QEMU, an operating system can run above software emulated CPU. How can be a CPU emulated by software? I want to know about detail.

If CPU is

Answer 1

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;