swi   #val   //val: bit[23:0]立即数,该val用来判断用户函数需要调用哪个内核函数

ENTRY(vector_swi)
           /*保护用户态的现场*/
sub  sp, sp, #S_FRAME_SIZEstmia      sp, {r0 - r12}                 @ Calling r0 - r12add r8, sp, #S_PCstmdb     r8, {sp, lr}^                   @ Calling sp, lrmrs  r8, spsr                 @ called from non-FIQ mode, so ok.str   lr, [sp, #S_PC]                @ Save calling PCstr   r8, [sp, #S_PSR]             @ Save CPSRstr   r0, [sp, #S_OLD_R0]              @ Save OLD_R0zero_fp... ...ldr   scno, [lr, #-4]                 @ get SWI instruction  //获取SWI值A710(       and  ip, scno, #0x0f000000 @ check for SWI)A710(       teq  ip, #0x0f000000)                               //校验SWI的bit[27:24]是否为0xfA710(       bne  .Larm710bug)... ...enable_irq                           //调用enable_irq()函数get_thread_info tskadr  tbl, sys_call_table            @ load syscall table pointer  // tbl等于数组表基地址ldr   ip, [tsk, #TI_FLAGS]          @ check for syscall tracing  ... ...bic  scno, scno, #0xff000000              @ mask off SWI op-code //只保留SWI的bit[23:0],也就是val值
eor  scno, scno, #__NR_SYSCALL_BASE @ check OS number
//对于2440而讲,__NR_SYSCALL_BASE基地址等于0x900000,也就是说val值为0x900000时,异或后,scno则等于0,表示数组表的基地址(第一个函数位置)
... ...ldrcc pc, [tbl, scno, lsl #2]             @ call sys_* routine          //pc=(tbl+scno)<<2,实现调用sys_write()//tbl:数组表基地址,  scno:要调用的sys_write()的索引值     lsl #2:左移2位,一个函数指针占据4个字节

swi  #0x900000

.equ NR_syscalls,0     //将NR_syscalls=0#define CALL(x) .equ NR_syscalls,NR_syscalls+1   //将CALL(x) 定义为：NR_syscalls=NR_syscalls+1 ,也就是每有一个CALL(),则该CALL值则+1#include "calls.S"              //将calls.S的内容包进来，CALL(x)上面已经有了定义,就会将calls.S里面的所有CALL(sys_xx)排列起来#undef CALL                    //撤销CALL定义#define CALL(x) .long x        //然后再将排列起来的sys_xx以long(4字节)对齐,一个函数指针占据4字节

asmlinkage void sys_hello(const char __user * buf, size_t count)     //打印count长数据
{char ker_buf[100];if(buf){ copy_from_user(ker_buf, buf, (count<100)? count : 100);ker_buf[99]='\0';printk("sys_hello:%s\n",ker_buf);}
}

asmlinkage void sys_hello(const char __user * buf, size_t count);

#include <errno.h>
#include <unistd.h>
#define __NR_SYSCALL_BASE       0x900000void hello(char *buf, int count)
{/* swi */asm ("mov r0, %0\n"   /* save the argment in r0 */  //%0等于buf "mov r1, %1\n"   /* save the argment in r0 */   //%1等于count"swi %2\n"   /* do the system call */        //%2等于0x900352:                                                       //输出部: "r"(buf), "r"(count), "i" (__NR_SYSCALL_BASE + 352)  //输入部: "r0", "r1");                     　　　　　　　　　　   //损坏部,指原有的数据会被破坏
}
int main(int argc, char **argv)
{printf("in app, call hello\n");hello("www.100ask.net", 15);//这个函数会调用内核的sys_hello()return 0;
}

int num=5,val;asm("mov %0,%1\n":"=r"(val)                //指定val是一个输出部,执行mov后,val便等于5:"i"(num)                // "i"约束条件字母,表示num是一个立即数:      );                

task_pt_regs(current);          //获取当前应用程序的各个寄存器内容,会返回一个pt_regs结构体