android调用号和libc

　　调用号(以arm平台为例)在/bionic/libc/kernel/uapi/asm-arm/asm/unistd.h：

/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define __NR_restart_syscall (__NR_SYSCALL_BASE+ 0)
#define __NR_exit (__NR_SYSCALL_BASE+ 1)
#define __NR_fork (__NR_SYSCALL_BASE+ 2)
#define __NR_read (__NR_SYSCALL_BASE+ 3)
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define __NR_write (__NR_SYSCALL_BASE+ 4)
#define __NR_open (__NR_SYSCALL_BASE+ 5)
#define __NR_close (__NR_SYSCALL_BASE+ 6)
#define __NR_creat (__NR_SYSCALL_BASE+ 8)
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define __NR_link (__NR_SYSCALL_BASE+ 9)
#define __NR_unlink (__NR_SYSCALL_BASE+ 10)
#define __NR_execve (__NR_SYSCALL_BASE+ 11)
#define __NR_chdir (__NR_SYSCALL_BASE+ 12)
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define __NR_time (__NR_SYSCALL_BASE+ 13)
#define __NR_mknod (__NR_SYSCALL_BASE+ 14)
#define __NR_chmod (__NR_SYSCALL_BASE+ 15)
#define __NR_lchown (__NR_SYSCALL_BASE+ 16)
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define __NR_lseek (__NR_SYSCALL_BASE+ 19)
#define __NR_getpid (__NR_SYSCALL_BASE+ 20)
#define __NR_mount (__NR_SYSCALL_BASE+ 21)
#define __NR_umount (__NR_SYSCALL_BASE+ 22)
......

 　如何使用呢，以android5.0源码中的关机代码为例： /system/core/libcutils/android_reboot.c

#include <unistd.h>
#include <sys/reboot.h>
#include <sys/syscall.h>　　　　　　　　　　　　//　　bionic/libc/include/sys/syscall.h
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
......
int android_reboot(int cmd, int flags UNUSED, char *arg)
108{
        ......
    switch (cmd) {
        ......
       case ANDROID_RB_RESTART2:
        ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,　　　　//   /bionic/libc/arch-arm/bionic/syscall.S
                           LINUX_REBOOT_CMD_RESTART2, arg);
        ......
}

 　　代码中直接syscall(_NR_reboot)来调用系统reboot函数，注意上面红色标注的代码。

　　(dannerWorking:要分析/bionic/libc/tools/gensyscalls.py这个文件啊还没做)

参考资料：

　1 android 系统调用