struct pt_regs的作用

pt_regs结构：
这个结构封装了需要在内核入口中保存的最少的状态信息。比如说每一次的系统调用、中断、陷阱、故障时，pt_regs结构中保存了最少的状态信息。
/*
 * This struct defines the way the registers are stored on the
 * stack during a system call.  Note that sizeof(struct pt_regs)
 * has to be a multiple of 8.
 */
#ifndef __KERNEL__
struct pt_regs {
        long uregs[18];
};
#else /* __KERNEL__ */
struct pt_regs {
        unsigned long uregs[18];
};
#endif /* __KERNEL__ */


#define ARM_cpsr        uregs[16]
#define ARM_pc          uregs[15]
#define ARM_lr          uregs[14]
#define ARM_sp          uregs[13]
#define ARM_ip          uregs[12]
#define ARM_fp          uregs[11]
#define ARM_r10         uregs[10]
#define ARM_r9          uregs[9]
#define ARM_r8          uregs[8]
#define ARM_r7          uregs[7]
#define ARM_r6          uregs[6]
#define ARM_r5          uregs[5]
#define ARM_r4          uregs[4]
#define ARM_r3          uregs[3]
#define ARM_r2          uregs[2]
#define ARM_r1          uregs[1]
#define ARM_r0          uregs[0]
#define ARM_ORIG_r0     uregs[17]

(S_FRAME_SIZE, sizeof(struct ));

 166/* 

 * These are the registers used in the syscall handler, and allow us to  * have in theory up to 7 arguments to a function - r0 to r6.  *  * r7 is reserved for the system call number for thumb mode.  *  * Note that tbl == why is intentional.  *  * We must set at least "tsk" and "why" when calling ret_with_reschedule. 

 */ 

 scno .req    r7 @ syscall number 

 tbl .req    r8 @ syscall table pointer 

 why .req    r8 @ Linux syscall (!= 0) 

 tsk .req    r9 @ current thread_info