ldd3-chapter5-syscall

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說明System Call

更新記錄

item note
20160613 第一版

目錄

system call

  • 通過library使用方式如下圖
  • Invoking the system call handler and executing a system call,來源

system call

  • 一般app都是通過library來呼叫kernl的system call
  • 也可以直接呼叫kernl的system call
    • ex.使用ioctl

linux kernel system call

於kernel, arch/arm/include/asm/unistd.h內有定義system call number

system call number

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#define __NR_OABI_SYSCALL_BASE  0x900000 

#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)                      
#define __NR_write          (__NR_SYSCALL_BASE+  4)                      
#define __NR_open           (__NR_SYSCALL_BASE+  5)                      
#define __NR_close          (__NR_SYSCALL_BASE+  6)                      
                     /* 7 was sys_waitpid */                              
#define __NR_creat          (__NR_SYSCALL_BASE+  8)                      
#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)                      
#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)

cpu system table">比對cpu system table

name register r7
restart_syscall 0x900000
exit 0x900001
fork 0x900002
read 0x900003
write 0x900004

通過ioctl的參數傳遞

  • 來源 ldd3 chapter5
  • 系統呼叫需檢查所有的參數，以確保它們是有效且合法的

  • 系統提供了兩個方法來進行必要的檢查，及在kernel space及user space之間進行所需要的複製

  • copy_to_user: Copy a block of data into user space. 

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unsigned long copy_to_user (	void __user *  	to,
	const void *  	from,
	unsigned long  	n);
parameter description
to Destination address,in user space
from Source address, in kernel space
n Number of bytes to copy.
  • copy_from_user: Copy a block of data from user space. 
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unsigned long copy_from_user (	void *  	to,
 	const void __user *  	from,
 	unsigned long  	n);
parameter description
to Destination address, in kernel space
from Source address, in user space
n Number of bytes to copy.

參考來源