Linux系統呼叫流程分析

一直很好奇系統呼叫的詳細過程，只簡單的瞭解系統呼叫是使用者與核心互動的藉口，看了幾天的內容，不知道從何下手開始寫，今天略有頭緒，做以簡單總結。

1，  什麼是系統呼叫。

系統呼叫：系統呼叫是作業系統為使用者提供的一系列API；系統呼叫將使用者的請求發給核心，核心執行完以後，將結果返回給使用者；

2， 一個系統呼叫的流程。

如上圖，是系統呼叫write()函式的呼叫過程，不難看出，在使用者開始呼叫系統呼叫時，觸發了軟中斷Int0X80。到這肯定有人疑問，為什麼中斷號是0X80，因為程式碼中把系統呼叫跟0X80繫結在一起。

中斷向量：一個記憶體單元，存放中斷處理程式入口地址和程式執行時所需處理機狀態字。

這裡不再深入講解向量表的生成，只需要知道每個中斷都有對應的中斷號並對應處理程式。

linux的中斷向量表：

a.0X80中斷號：

/*
 * 我們需要下面這些內嵌語句- 從核心空間建立程序(forking)將導致沒有寫時復
 * 制（COPY ON WRITE）!!!直到一個執行execve 呼叫。這對堆疊可能帶來問題。處
 * 理的方法是在fork()呼叫之後不讓main()使用任何堆疊。因此就不能有函式調
 * 用- 這意味著fork 也要使用內嵌的程式碼，否則我們在從fork()退出時就要使用堆疊了。
 *
 * 實際上只有pause 和fork 需要使用內嵌方式，以保證從main()中不會弄亂堆疊，
 * 但是我們同時還定義了其它一些函式。
 */
 
/*
_syscall0 是unistd.h 中的內嵌巨集程式碼。以嵌入彙編的形式呼叫Linux 的系統呼叫中斷0x80。
Linux 的系統呼叫中斷0x80，該中斷是所有系統呼叫的入口。
syscall0 名稱中最後的0 表示無引數，1 表示1 個引數。
*/
static _inline _syscall0(int,fork)
											
static _inline _syscall0(int,pause)				// int pause()系統呼叫：暫停程序的執行，直到收到一個訊號。
								
static _inline _syscall1(int,setup,void *,BIOS)	// int setup(void * BIOS)系統呼叫，僅用於linux 初始化（僅在這個程式中被呼叫）。
												
static _inline _syscall0(int,sync)				// int sync()系統呼叫：更新檔案系統。

#include <linux/tty.h>	// tty 標頭檔案，定義了有關tty_io，序列通訊方面的
									// 引數、常數。
#include <linux/sched.h>	// 排程程式標頭檔案，定義了任務結構task_struct、第1 個
									// 初始任務的資料。還有一些以巨集的形式定義的有關描述符
									// 引數設定和獲取的嵌入式彙編函式程式。
#include <linux/head.h>	// head 標頭檔案，定義了段描述符的簡單結構，
									// 和幾個選擇符常量。
#include <asm/system.h>	// 系統標頭檔案。以巨集的形式定義了許多有關設定或修改
									// 描述符/中斷門等的嵌入式彙編子程式。
#include <asm/io.h>		// io 標頭檔案。以巨集的嵌入彙編程式形式定義對io 端
									// 口操作的函式。

#include <stddef.h>	// 標準定義標頭檔案。定義了NULL, offsetof(TYPE, MEMBER)。
#include <stdarg.h>	// 標準引數標頭檔案。以巨集的形式定義變數引數列表。主要說
								// 明瞭-個型別(va_list)和三個巨集(va_start, va_arg 和
								// va_end)，vsprintf、vprintf、vfprintf。
#include <fcntl.h>	// 檔案控制標頭檔案。用於檔案及其描述符的操作控制常數
								// 符號的定義。
#include <sys/types.h>// 型別標頭檔案。定義了基本的系統資料型別。

#include <linux/fs.h>// 檔案系統標頭檔案。定義檔案表結構
								//（file,buffer_head,m_inode 等）。

static char printbuf[1024];

extern int vsprintf();								// 送格式化輸出到一字串中（在kernel/vsprintf.c）。
extern void init(void);								// 函式原形，初始化（在後面）。
extern void blk_dev_init(void);						// 塊裝置初始化子程式（kernel/blk_drv/ll_rw_blk.c）
extern void chr_dev_init(void);						// 字元裝置初始化（kernel/chr_drv/tty_io.c）
extern void hd_init(void);							// 硬碟初始化程式（kernel/blk_drv/hd.c）
extern void floppy_init(void);						// 軟碟機初始化程式（kernel/blk_drv/floppy.c）
extern void mem_init(long start, long end);			// 記憶體管理初始化（mm/memory.c）
extern long rd_init(long mem_start, int length);	//虛擬盤初始化(kernel/blk_drv/ramdisk.c)
extern long kernel_mktime(struct tm * tm);			// 建立核心時間（秒）。
extern long startup_time;							// 核心啟動時間（開機時間）（秒）。

/*
 * 以下這些資料是由setup.s 程式在引導時間設定的。
 */
#define EXT_MEM_K (*(unsigned short *)0x90002)		// 1M 以後的擴充套件記憶體大小（KB）。
#define DRIVE_INFO (*(struct drive_info *)0x90080)	// 硬碟引數表基址。
#define ORIG_ROOT_DEV (*(unsigned short *)0x901FC)	// 根檔案系統所在裝置號。

/*
 * 是啊，是啊，下面這段程式很差勁，但我不知道如何正確地實現，而且好象
 * 它還能執行。如果有關於實時時鐘更多的資料，那我很感興趣。這些都是試
 * 探出來的，以及看了一些bios 程式，呵！
 */
 
// 這段巨集讀取CMOS 實時時鐘資訊。
// 0x70 是寫埠號，0x80|addr 是要讀取的CMOS 記憶體地址。
// 0x71 是讀埠號。
/*
#define CMOS_READ(addr) ({ \
outb_p(0x80|addr,0x70); \
inb_p(0x71); \
})*/
_inline unsigned char CMOS_READ(unsigned char addr)
{
	outb_p(addr,0x70);
	return inb_p(0x71);
}
 

下面是_system_call的彙編程式碼(asm.S)：

_system_call:
	cmp eax,nr_system_calls-1 ;// 呼叫號如果超出範圍的話就在eax 中置-1 並退出。
	ja bad_sys_call
	push ds ;// 儲存原段暫存器值。
	push es
	push fs
	push edx ;// ebx,ecx,edx 中放著系統呼叫相應的C 語言函式的呼叫引數。
	push ecx ;// push %ebx,%ecx,%edx as parameters
	push ebx ;// to the system call
	mov edx,10h ;// set up ds,es to kernel space
	mov ds,dx ;// ds,es 指向核心資料段(全域性描述符表中資料段描述符)。
	mov es,dx
	mov edx,17h ;// fs points to local data space
	mov fs,dx ;// fs 指向區域性資料段(區域性描述符表中資料段描述符)。
;// 下面這句運算元的含義是：呼叫地址 = _sys_call_table + %eax * 4。參見列表後的說明。
;// 對應的C 程式中的sys_call_table 在include/linux/sys.h 中，其中定義了一個包括72 個
;// 系統呼叫C 處理函式的地址陣列表。
	call [_sys_call_table+eax*4]
	push eax ;// 把系統呼叫號入棧。
	mov eax,_current ;// 取當前任務（程序）資料結構地址??eax。
;// 下面97-100 行檢視當前任務的執行狀態。如果不在就緒狀態(state 不等於0)就去執行排程程式。
;// 如果該任務在就緒狀態但counter[??]值等於0，則也去執行排程程式。
	cmp dword ptr [state+eax],0 ;// state
	jne reschedule
	cmp dword ptr [counter+eax],0 ;// counter
	je reschedule
 

b.現場保護與恢復

因為使用者態和核心態不共用一個堆疊，所以使用者態呼叫系統呼叫時，得先儲存使用者態的資訊到暫存器，然後切入到核心態，將暫存器中的資訊拷貝到核心棧開始執行，執行結束後，還原之前使用者態的狀態讓使用者態繼續往下執行。

使用者態程式通過ebx,ecx,edx等暫存器，傳遞函式引數給系統呼叫，ebx,ecx,edx等暫存器通過SAVE_ALL巨集壓到核心棧。

系統呼叫結束之後，RESTORE_ALL巨集把SAVE_ALL巨集壓入的暫存器反向彈出，以用於恢復現場。

c.呼叫系統呼叫表

syscall_handler_t *sys_call_table[] = {
	[ __NR_restart_syscall ] = (syscall_handler_t *) sys_restart_syscall,
	[ __NR_exit ] = (syscall_handler_t *) sys_exit,
	[ __NR_fork ] = (syscall_handler_t *) sys_fork,
	[ __NR_read ] = (syscall_handler_t *) sys_read,
	[ __NR_write ] = (syscall_handler_t *) sys_write,

	/* These three are declared differently in asm/unistd.h */
	[ __NR_open ] = (syscall_handler_t *) sys_open,
	[ __NR_close ] = (syscall_handler_t *) sys_close,
	[ __NR_creat ] = (syscall_handler_t *) sys_creat,
	[ __NR_link ] = (syscall_handler_t *) sys_link,
	[ __NR_unlink ] = (syscall_handler_t *) sys_unlink,
	[ __NR_execve ] = (syscall_handler_t *) sys_execve,

	/* declared differently in kern_util.h */
	[ __NR_chdir ] = (syscall_handler_t *) sys_chdir,
	[ __NR_time ] = um_time,
	[ __NR_mknod ] = (syscall_handler_t *) sys_mknod,
	[ __NR_chmod ] = (syscall_handler_t *) sys_chmod,
	[ __NR_lchown ] = (syscall_handler_t *) sys_lchown16,
	[ __NR_lseek ] = (syscall_handler_t *) sys_lseek,
	[ __NR_getpid ] = (syscall_handler_t *) sys_getpid,
	[ __NR_mount ] = um_mount,
	[ __NR_setuid ] = (syscall_handler_t *) sys_setuid16,
	[ __NR_getuid ] = (syscall_handler_t *) sys_getuid16,
 	[ __NR_ptrace ] = (syscall_handler_t *) sys_ptrace,
	[ __NR_alarm ] = (syscall_handler_t *) sys_alarm,
	[ __NR_pause ] = (syscall_handler_t *) sys_pause,
	[ __NR_utime ] = (syscall_handler_t *) sys_utime,
	[ __NR_access ] = (syscall_handler_t *) sys_access,
	[ __NR_sync ] = (syscall_handler_t *) sys_sync,
	[ __NR_kill ] = (syscall_handler_t *) sys_kill,
	[ __NR_rename ] = (syscall_handler_t *) sys_rename,
	[ __NR_mkdir ] = (syscall_handler_t *) sys_mkdir,
	[ __NR_rmdir ] = (syscall_handler_t *) sys_rmdir,

	/* Declared differently in asm/unistd.h */
	[ __NR_dup ] = (syscall_handler_t *) sys_dup,
	[ __NR_pipe ] = (syscall_handler_t *) sys_pipe,
	[ __NR_times ] = (syscall_handler_t *) sys_times,
	[ __NR_brk ] = (syscall_handler_t *) sys_brk,
	[ __NR_setgid ] = (syscall_handler_t *) sys_setgid16,
	[ __NR_getgid ] = (syscall_handler_t *) sys_getgid16,
	[ __NR_geteuid ] = (syscall_handler_t *) sys_geteuid16,
	[ __NR_getegid ] = (syscall_handler_t *) sys_getegid16,
	[ __NR_acct ] = (syscall_handler_t *) sys_acct,
	[ __NR_umount2 ] = (syscall_handler_t *) sys_umount,
	[ __NR_ioctl ] = (syscall_handler_t *) sys_ioctl,
	[ __NR_fcntl ] = (syscall_handler_t *) sys_fcntl,
	[ __NR_setpgid ] = (syscall_handler_t *) sys_setpgid,
	[ __NR_umask ] = (syscall_handler_t *) sys_umask,
	[ __NR_chroot ] = (syscall_handler_t *) sys_chroot,
	[ __NR_ustat ] = (syscall_handler_t *) sys_ustat,
	[ __NR_dup2 ] = (syscall_handler_t *) sys_dup2,
	[ __NR_getppid ] = (syscall_handler_t *) sys_getppid,
	[ __NR_getpgrp ] = (syscall_handler_t *) sys_getpgrp,
	[ __NR_setsid ] = (syscall_handler_t *) sys_setsid,
	[ __NR_setreuid ] = (syscall_handler_t *) sys_setreuid16,
	[ __NR_setregid ] = (syscall_handler_t *) sys_setregid16,
	[ __NR_sethostname ] = (syscall_handler_t *) sys_sethostname,
	[ __NR_setrlimit ] = (syscall_handler_t *) sys_setrlimit,
	[ __NR_getrlimit ] = (syscall_handler_t *) sys_old_getrlimit,
	[ __NR_getrusage ] = (syscall_handler_t *) sys_getrusage,
	[ __NR_gettimeofday ] = (syscall_handler_t *) sys_gettimeofday,
	[ __NR_settimeofday ] = (syscall_handler_t *) sys_settimeofday,
	[ __NR_getgroups ] = (syscall_handler_t *) sys_getgroups16,
	[ __NR_setgroups ] = (syscall_handler_t *) sys_setgroups16,
	[ __NR_symlink ] = (syscall_handler_t *) sys_symlink,
	[ __NR_readlink ] = (syscall_handler_t *) sys_readlink,
	[ __NR_uselib ] = (syscall_handler_t *) sys_uselib,
	[ __NR_swapon ] = (syscall_handler_t *) sys_swapon,
	[ __NR_reboot ] = (syscall_handler_t *) sys_reboot,
	[ __NR_munmap ] = (syscall_handler_t *) sys_munmap,
	[ __NR_truncate ] = (syscall_handler_t *) sys_truncate,
	[ __NR_ftruncate ] = (syscall_handler_t *) sys_ftruncate,
	[ __NR_fchmod ] = (syscall_handler_t *) sys_fchmod,
	[ __NR_fchown ] = (syscall_handler_t *) sys_fchown16,
	[ __NR_getpriority ] = (syscall_handler_t *) sys_getpriority,
	[ __NR_setpriority ] = (syscall_handler_t *) sys_setpriority,
	[ __NR_statfs ] = (syscall_handler_t *) sys_statfs,
	[ __NR_fstatfs ] = (syscall_handler_t *) sys_fstatfs,
	[ __NR_ioperm ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_syslog ] = (syscall_handler_t *) sys_syslog,
	[ __NR_setitimer ] = (syscall_handler_t *) sys_setitimer,
	[ __NR_getitimer ] = (syscall_handler_t *) sys_getitimer,
	[ __NR_stat ] = (syscall_handler_t *) sys_newstat,
	[ __NR_lstat ] = (syscall_handler_t *) sys_newlstat,
	[ __NR_fstat ] = (syscall_handler_t *) sys_newfstat,
	[ __NR_vhangup ] = (syscall_handler_t *) sys_vhangup,
	[ __NR_wait4 ] = (syscall_handler_t *) sys_wait4,
	[ __NR_swapoff ] = (syscall_handler_t *) sys_swapoff,
	[ __NR_sysinfo ] = (syscall_handler_t *) sys_sysinfo,
	[ __NR_fsync ] = (syscall_handler_t *) sys_fsync,
	[ __NR_clone ] = (syscall_handler_t *) sys_clone,
	[ __NR_setdomainname ] = (syscall_handler_t *) sys_setdomainname,
	[ __NR_uname ] = (syscall_handler_t *) sys_newuname,
	[ __NR_adjtimex ] = (syscall_handler_t *) sys_adjtimex,
	[ __NR_mprotect ] = (syscall_handler_t *) sys_mprotect,
	[ __NR_create_module ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_init_module ] = (syscall_handler_t *) sys_init_module,
	[ __NR_delete_module ] = (syscall_handler_t *) sys_delete_module,
	[ __NR_get_kernel_syms ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_quotactl ] = (syscall_handler_t *) sys_quotactl,
	[ __NR_getpgid ] = (syscall_handler_t *) sys_getpgid,
	[ __NR_fchdir ] = (syscall_handler_t *) sys_fchdir,
	[ __NR_sysfs ] = (syscall_handler_t *) sys_sysfs,
	[ __NR_personality ] = (syscall_handler_t *) sys_personality,
	[ __NR_afs_syscall ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_setfsuid ] = (syscall_handler_t *) sys_setfsuid16,
	[ __NR_setfsgid ] = (syscall_handler_t *) sys_setfsgid16,
	[ __NR_getdents ] = (syscall_handler_t *) sys_getdents,
	[ __NR_flock ] = (syscall_handler_t *) sys_flock,
	[ __NR_msync ] = (syscall_handler_t *) sys_msync,
	[ __NR_readv ] = (syscall_handler_t *) sys_readv,
	[ __NR_writev ] = (syscall_handler_t *) sys_writev,
	[ __NR_getsid ] = (syscall_handler_t *) sys_getsid,
	[ __NR_fdatasync ] = (syscall_handler_t *) sys_fdatasync,
	[ __NR__sysctl ] = (syscall_handler_t *) sys_sysctl,
	[ __NR_mlock ] = (syscall_handler_t *) sys_mlock,
	[ __NR_munlock ] = (syscall_handler_t *) sys_munlock,
	[ __NR_mlockall ] = (syscall_handler_t *) sys_mlockall,
	[ __NR_munlockall ] = (syscall_handler_t *) sys_munlockall,
	[ __NR_sched_setparam ] = (syscall_handler_t *) sys_sched_setparam,
	[ __NR_sched_getparam ] = (syscall_handler_t *) sys_sched_getparam,
	[ __NR_sched_setscheduler ] = (syscall_handler_t *) sys_sched_setscheduler,
	[ __NR_sched_getscheduler ] = (syscall_handler_t *) sys_sched_getscheduler,
	[ __NR_sched_yield ] = (syscall_handler_t *) yield,
	[ __NR_sched_get_priority_max ] = (syscall_handler_t *) sys_sched_get_priority_max,
	[ __NR_sched_get_priority_min ] = (syscall_handler_t *) sys_sched_get_priority_min,
	[ __NR_sched_rr_get_interval ] = (syscall_handler_t *) sys_sched_rr_get_interval,
	[ __NR_nanosleep ] = (syscall_handler_t *) sys_nanosleep,
	[ __NR_mremap ] = (syscall_handler_t *) sys_mremap,
	[ __NR_setresuid ] = (syscall_handler_t *) sys_setresuid16,
	[ __NR_getresuid ] = (syscall_handler_t *) sys_getresuid16,
	[ __NR_query_module ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_poll ] = (syscall_handler_t *) sys_poll,
	[ __NR_nfsservctl ] = (syscall_handler_t *) NFSSERVCTL,
	[ __NR_setresgid ] = (syscall_handler_t *) sys_setresgid16,
	[ __NR_getresgid ] = (syscall_handler_t *) sys_getresgid16,
	[ __NR_prctl ] = (syscall_handler_t *) sys_prctl,
	[ __NR_rt_sigreturn ] = (syscall_handler_t *) sys_rt_sigreturn,
	[ __NR_rt_sigaction ] = (syscall_handler_t *) sys_rt_sigaction,
	[ __NR_rt_sigprocmask ] = (syscall_handler_t *) sys_rt_sigprocmask,
	[ __NR_rt_sigpending ] = (syscall_handler_t *) sys_rt_sigpending,
	[ __NR_rt_sigtimedwait ] = (syscall_handler_t *) sys_rt_sigtimedwait,
	[ __NR_rt_sigqueueinfo ] = (syscall_handler_t *) sys_rt_sigqueueinfo,
	[ __NR_rt_sigsuspend ] = (syscall_handler_t *) sys_rt_sigsuspend,
	[ __NR_pread64 ] = (syscall_handler_t *) sys_pread64,
	[ __NR_pwrite64 ] = (syscall_handler_t *) sys_pwrite64,
	[ __NR_chown ] = (syscall_handler_t *) sys_chown16,
	[ __NR_getcwd ] = (syscall_handler_t *) sys_getcwd,
	[ __NR_capget ] = (syscall_handler_t *) sys_capget,
	[ __NR_capset ] = (syscall_handler_t *) sys_capset,
	[ __NR_sigaltstack ] = (syscall_handler_t *) sys_sigaltstack,
	[ __NR_sendfile ] = (syscall_handler_t *) sys_sendfile,
	[ __NR_getpmsg ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_putpmsg ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_vfork ] = (syscall_handler_t *) sys_vfork,
	[ __NR_getdents64 ] = (syscall_handler_t *) sys_getdents64,
	[ __NR_gettid ] = (syscall_handler_t *) sys_gettid,
	[ __NR_readahead ] = (syscall_handler_t *) sys_readahead,
	[ __NR_setxattr ] = (syscall_handler_t *) sys_setxattr,
	[ __NR_lsetxattr ] = (syscall_handler_t *) sys_lsetxattr,
	[ __NR_fsetxattr ] = (syscall_handler_t *) sys_fsetxattr,
	[ __NR_getxattr ] = (syscall_handler_t *) sys_getxattr,
	[ __NR_lgetxattr ] = (syscall_handler_t *) sys_lgetxattr,
	[ __NR_fgetxattr ] = (syscall_handler_t *) sys_fgetxattr,
	[ __NR_listxattr ] = (syscall_handler_t *) sys_listxattr,
	[ __NR_llistxattr ] = (syscall_handler_t *) sys_llistxattr,
	[ __NR_flistxattr ] = (syscall_handler_t *) sys_flistxattr,
	[ __NR_removexattr ] = (syscall_handler_t *) sys_removexattr,
	[ __NR_lremovexattr ] = (syscall_handler_t *) sys_lremovexattr,
	[ __NR_fremovexattr ] = (syscall_handler_t *) sys_fremovexattr,
	[ __NR_tkill ] = (syscall_handler_t *) sys_tkill,
	[ __NR_futex ] = (syscall_handler_t *) sys_futex,
	[ __NR_sched_setaffinity ] = (syscall_handler_t *) sys_sched_setaffinity,
	[ __NR_sched_getaffinity ] = (syscall_handler_t *) sys_sched_getaffinity,
	[ __NR_io_setup ] = (syscall_handler_t *) sys_io_setup,
	[ __NR_io_destroy ] = (syscall_handler_t *) sys_io_destroy,
	[ __NR_io_getevents ] = (syscall_handler_t *) sys_io_getevents,
	[ __NR_io_submit ] = (syscall_handler_t *) sys_io_submit,
	[ __NR_io_cancel ] = (syscall_handler_t *) sys_io_cancel,
	[ __NR_exit_group ] = (syscall_handler_t *) sys_exit_group,
	[ __NR_lookup_dcookie ] = (syscall_handler_t *) sys_lookup_dcookie,
	[ __NR_epoll_create ] = (syscall_handler_t *) sys_epoll_create,
	[ __NR_epoll_ctl ] = (syscall_handler_t *) sys_epoll_ctl,
	[ __NR_epoll_wait ] = (syscall_handler_t *) sys_epoll_wait,
        [ __NR_set_tid_address ] = (syscall_handler_t *) sys_set_tid_address,
	[ __NR_timer_create ] = (syscall_handler_t *) sys_timer_create,
	[ __NR_timer_settime ] = (syscall_handler_t *) sys_timer_settime,
	[ __NR_timer_gettime ] = (syscall_handler_t *) sys_timer_gettime,
	[ __NR_timer_getoverrun ] = (syscall_handler_t *) sys_timer_getoverrun,
	[ __NR_timer_delete ] = (syscall_handler_t *) sys_timer_delete,
	[ __NR_clock_settime ] = (syscall_handler_t *) sys_clock_settime,
	[ __NR_clock_gettime ] = (syscall_handler_t *) sys_clock_gettime,
	[ __NR_clock_getres ] = (syscall_handler_t *) sys_clock_getres,
	[ __NR_clock_nanosleep ] = (syscall_handler_t *) sys_clock_nanosleep,
	[ __NR_statfs64 ] = (syscall_handler_t *) sys_statfs64,
	[ __NR_fstatfs64 ] = (syscall_handler_t *) sys_fstatfs64,
	[ __NR_tgkill ] = (syscall_handler_t *) sys_tgkill,
	[ __NR_utimes ] = (syscall_handler_t *) sys_utimes,
	[ __NR_fadvise64_64 ] = (syscall_handler_t *) sys_fadvise64_64,
	[ __NR_vserver ] = (syscall_handler_t *) sys_vserver,
	[ __NR_mbind ] = (syscall_handler_t *) sys_mbind,
	[ __NR_get_mempolicy ] = (syscall_handler_t *) sys_get_mempolicy,
	[ __NR_set_mempolicy ] = (syscall_handler_t *) sys_set_mempolicy,
	[ __NR_mq_open ] = (syscall_handler_t *) sys_mq_open,
	[ __NR_mq_unlink ] = (syscall_handler_t *) sys_mq_unlink,
	[ __NR_mq_timedsend ] = (syscall_handler_t *) sys_mq_timedsend,
	[ __NR_mq_timedreceive ] = (syscall_handler_t *) sys_mq_timedreceive,
	[ __NR_mq_notify ] = (syscall_handler_t *) sys_mq_notify,
	[ __NR_mq_getsetattr ] = (syscall_handler_t *) sys_mq_getsetattr,
	[ __NR_sys_kexec_load ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_waitid ] = (syscall_handler_t *) sys_waitid,
	[ 285 ] = (syscall_handler_t *) sys_ni_syscall,
	[ __NR_add_key ] = (syscall_handler_t *) sys_add_key,
	[ __NR_request_key ] = (syscall_handler_t *) sys_request_key,
	[ __NR_keyctl ] = (syscall_handler_t *) sys_keyctl,

	ARCH_SYSCALLS
	[ LAST_SYSCALL + 1 ... NR_syscalls ] = 
	        (syscall_handler_t *) sys_ni_syscall
};

從這裡會跳轉到具體的系統呼叫。

每個系統呼叫對應一個呼叫號（unistd.h）

#ifndef _ALPHA_UNISTD_H
#define _ALPHA_UNISTD_H

#define __NR_osf_syscall	  0	/* not implemented */
#define __NR_exit		  1
#define __NR_fork		  2
#define __NR_read		  3
#define __NR_write		  4
#define __NR_osf_old_open	  5	/* not implemented */
#define __NR_close		  6
#define __NR_osf_wait4		  7
#define __NR_osf_old_creat	  8	/* not implemented */
#define __NR_link		  9
#define __NR_unlink		 10
#define __NR_osf_execve		 11	/* not implemented */
#define __NR_chdir		 12
#define __NR_fchdir		 13
#define __NR_mknod		 14
#define __NR_chmod		 15
#define __NR_chown		 16
#define __NR_brk		 17
#define __NR_osf_getfsstat	 18	/* not implemented */
#define __NR_lseek		 19
#define __NR_getxpid		 20
#define __NR_osf_mount		 21
#define __NR_umount		 22
#define __NR_setuid		 23
#define __NR_getxuid		 24
#define __NR_exec_with_loader	 25	/* not implemented */
#define __NR_ptrace		 26
#define __NR_osf_nrecvmsg	 27	/* not implemented */
#define __NR_osf_nsendmsg	 28	/* not implemented */
#define __NR_osf_nrecvfrom	 29	/* not implemented */
#define __NR_osf_naccept	 30	/* not implemented */
#define __NR_osf_ngetpeername	 31	/* not implemented */
#define __NR_osf_ngetsockname	 32	/* not implemented */
#define __NR_access		 33
#define __NR_osf_chflags	 34	/* not implemented */
#define __NR_osf_fchflags	 35	/* not implemented */
#define __NR_sync		 36
#define __NR_kill		 37
#define __NR_osf_old_stat	 38	/* not implemented */
#define __NR_setpgid		 39
#define __NR_osf_old_lstat	 40	/* not implemented */
#define __NR_dup		 41
#define __NR_pipe		 42
#define __NR_osf_set_program_attributes	43
#define __NR_osf_profil		 44	/* not implemented */
#define __NR_open		 45
#define __NR_osf_old_sigaction	 46	/* not implemented */
#define __NR_getxgid		 47
#define __NR_osf_sigprocmask	 48
#define __NR_osf_getlogin	 49	/* not implemented */
#define __NR_osf_setlogin	 50	/* not implemented */
#define __NR_acct		 51
#define __NR_sigpending		 52

#define __NR_ioctl		 54
#define __NR_osf_reboot		 55	/* not implemented */
#define __NR_osf_revoke		 56	/* not implemented */
#define __NR_symlink		 57
#define __NR_readlink		 58
#define __NR_execve		 59
#define __NR_umask		 60
#define __NR_chroot		 61
#define __NR_osf_old_fstat	 62	/* not implemented */
#define __NR_getpgrp		 63
#define __NR_getpagesize	 64
#define __NR_osf_mremap		 65	/* not implemented */
#define __NR_vfork		 66
#define __NR_stat		 67
#define __NR_lstat		 68
#define __NR_osf_sbrk		 69	/* not implemented */
#define __NR_osf_sstk		 70	/* not implemented */
#define __NR_mmap		 71	/* OSF/1 mmap is superset of Linux */
#define __NR_osf_old_vadvise	 72	/* not implemented */
#define __NR_munmap		 73
#define __NR_mprotect		 74
#define __NR_madvise		 75
#define __NR_vhangup		 76
#define __NR_osf_kmodcall	 77	/* not implemented */
#define __NR_osf_mincore	 78	/* not implemented */
#define __NR_getgroups		 79
#define __NR_setgroups		 80
#define __NR_osf_old_getpgrp	 81	/* not implemented */
#define __NR_setpgrp		 82	/* BSD alias for setpgid */
#define __NR_osf_setitimer	 83
#define __NR_osf_old_wait	 84	/* not implemented */
#define __NR_osf_table		 85	/* not implemented */
#define __NR_osf_getitimer	 86
#define __NR_gethostname	 87
#define __NR_sethostname	 88
#define __NR_getdtablesize	 89
#define __NR_dup2		 90
#define __NR_fstat		 91
#define __NR_fcntl		 92
#define __NR_osf_select		 93
#define __NR_poll		 94
#define __NR_fsync		 95
#define __NR_setpriority	 96
#define __NR_socket		 97
#define __NR_connect		 98
#define __NR_accept		 99
#define __NR_getpriority	100

..........