参考：Linux异常处理体系结构

linux系统调用表(system call table)

　　  Arm Linux系统调用流程详细解析-SWI

ARM系统调用是通过SWI异常处理函数实现的，这里简要概述系统调用流程。

arch/arm/kernel/entry-armv.S中定义的vector_swi负责处理系统调用，代码如下

ENTRY(vector_swi)

    sub    sp, sp, #S_FRAME_SIZE

    stmia    sp, {r0 - r12}            @ Calling r0 - r12

    add    r8, sp, #S_PC

    stmdb    r8, {sp, lr}^            @ Calling sp, lr

    mrs    r8, spsr            @ called from non-FIQ mode, so ok.

    str    lr, [sp, #S_PC]            @ Save calling PC

    str    r8, [sp, #S_PSR]        @ Save CPSR

    str    r0, [sp, #S_OLD_R0]        @ Save OLD_R0

    zero_fp

    /*

     * Get the system call number.

     */

#if defined(CONFIG_OABI_COMPAT)

    /*

     * If we have CONFIG_OABI_COMPAT then we need to look at the swi

     * value to determine if it is an EABI or an old ABI call.

     */

#ifdef CONFIG_ARM_THUMB

    tst    r8, #PSR_T_BIT

    movne    r10, #                @ no thumb OABI emulation

    ldreq    r10, [lr, #-]            @ get SWI instruction

#else

    ldr    r10, [lr, #-]            @ get SWI instruction

  A710(    and    ip, r10, #0x0f000000        @ check for SWI        )

  A710(    teq    ip, #0x0f000000                        )

  A710(    bne    .Larm710bug                        )

#endif

#elif defined(CONFIG_AEABI)

    /*

     * Pure EABI user space always put syscall number into scno (r7).

     */

  A710(    ldr    ip, [lr, #-]            @ get SWI instruction    )

  A710(    and    ip, ip, #0x0f000000        @ check for SWI        )

  A710(    teq    ip, #0x0f000000                        )

  A710(    bne    .Larm710bug                        )

#elif defined(CONFIG_ARM_THUMB)

    /* Legacy ABI only, possibly thumb mode. */

    tst    r8, #PSR_T_BIT            @ this is SPSR from save_user_regs

    addne    scno, r7, #__NR_SYSCALL_BASE    @ put OS number in

    ldreq    scno, [lr, #-]

#else

    /* Legacy ABI only. */

    ldr    scno, [lr, #-]            @ get SWI instruction

  A710(    and    ip, scno, #0x0f000000        @ check for SWI        )

  A710(    teq    ip, #0x0f000000                        )

  A710(    bne    .Larm710bug                        )

#endif

#ifdef CONFIG_ALIGNMENT_TRAP

    ldr    ip, __cr_alignment

    ldr    ip, [ip]

    mcr    p15, , ip, c1, c0        @ update control register

#endif

    enable_irq

    get_thread_info tsk

    adr    tbl, sys_call_table        @ load syscall table pointer

    ldr    ip, [tsk, #TI_FLAGS]        @ check for syscall tracing

#if defined(CONFIG_OABI_COMPAT)

    /*

     * If the swi argument is zero, this is an EABI call and we do nothing.

     *

     * If this is an old ABI call, get the syscall number into scno and

     * get the old ABI syscall table address.

     */

    bics    r10, r10, #0xff000000

    eorne    scno, r10, #__NR_OABI_SYSCALL_BASE

    ldrne    tbl, =sys_oabi_call_table

#elif !defined(CONFIG_AEABI)

    bic    scno, scno, #0xff000000        @ mask off SWI op-code

    eor    scno, scno, #__NR_SYSCALL_BASE    @ check OS number

#endif

    stmdb    sp!, {r4, r5}            @ push fifth and sixth args

    tst    ip, #_TIF_SYSCALL_TRACE        @ are we tracing syscalls?

    bne    __sys_trace

    cmp    scno, #NR_syscalls        @ check upper syscall limit

    adr    lr, ret_fast_syscall        @ return address

    ldrcc    pc, [tbl, scno, lsl #]        @ call sys_* routine

    add    r1, sp, #S_OFF

:    mov    why, #                @ no longer a real syscall

    cmp    scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE)

    eor    r0, scno, #__NR_SYSCALL_BASE    @ put OS number back

    bcs    arm_syscall

    b    sys_ni_syscall            @ not private func

ENDPROC(vector_swi)

vector_swi

1.第一次包含linux/arch/arm/kernel/calls.S，计算系统调用接口的个数，包存在NR_syscalls中，对齐到4的倍数。

/*

 *  linux/arch/arm/kernel/calls.S

 *

 *  Copyright (C) 1995-2005 Russell King

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 *  This file is included thrice in entry-common.S

 */

/* 0 */        CALL(sys_restart_syscall)

        CALL(sys_exit)

        CALL(sys_fork_wrapper)

        CALL(sys_read)

        CALL(sys_write)

/* 5 */        CALL(sys_open)

        CALL(sys_close)

        CALL(sys_ni_syscall)        /* was sys_waitpid */

        CALL(sys_creat)

        CALL(sys_link)

/* 10 */    CALL(sys_unlink)

        CALL(sys_execve_wrapper)

        CALL(sys_chdir)

        CALL(OBSOLETE(sys_time))    /* used by libc4 */

        CALL(sys_mknod)

/* 15 */    CALL(sys_chmod)

        CALL(sys_lchown16)

        CALL(sys_ni_syscall)        /* was sys_break */

        CALL(sys_ni_syscall)        /* was sys_stat */

        CALL(sys_lseek)

/* 20 */    CALL(sys_getpid)

        CALL(sys_mount)

        CALL(OBSOLETE(sys_oldumount))    /* used by libc4 */

        CALL(sys_setuid16)

        CALL(sys_getuid16)

/* 25 */    CALL(OBSOLETE(sys_stime))

        CALL(sys_ptrace)

        CALL(OBSOLETE(sys_alarm))    /* used by libc4 */

        CALL(sys_ni_syscall)        /* was sys_fstat */

        CALL(sys_pause)

/* 30 */    CALL(OBSOLETE(sys_utime))    /* used by libc4 */

        CALL(sys_ni_syscall)        /* was sys_stty */

        CALL(sys_ni_syscall)        /* was sys_getty */

        CALL(sys_access)

        CALL(sys_nice)

/* 35 */    CALL(sys_ni_syscall)        /* was sys_ftime */

        CALL(sys_sync)

        CALL(sys_kill)

        CALL(sys_rename)

        CALL(sys_mkdir)

/* 40 */    CALL(sys_rmdir)

        CALL(sys_dup)

        CALL(sys_pipe)

        CALL(sys_times)

        CALL(sys_ni_syscall)        /* was sys_prof */

/* 45 */    CALL(sys_brk)

        CALL(sys_setgid16)

        CALL(sys_getgid16)

        CALL(sys_ni_syscall)        /* was sys_signal */

        CALL(sys_geteuid16)

/* 50 */    CALL(sys_getegid16)

        CALL(sys_acct)

        CALL(sys_umount)

        CALL(sys_ni_syscall)        /* was sys_lock */

        CALL(sys_ioctl)

/* 55 */    CALL(sys_fcntl)

        CALL(sys_ni_syscall)        /* was sys_mpx */

        CALL(sys_setpgid)

        CALL(sys_ni_syscall)        /* was sys_ulimit */

        CALL(sys_ni_syscall)        /* was sys_olduname */

/* 60 */    CALL(sys_umask)

        CALL(sys_chroot)

        CALL(sys_ustat)

        CALL(sys_dup2)

        CALL(sys_getppid)

/* 65 */    CALL(sys_getpgrp)

        CALL(sys_setsid)

        CALL(sys_sigaction)

        CALL(sys_ni_syscall)        /* was sys_sgetmask */

        CALL(sys_ni_syscall)        /* was sys_ssetmask */

/* 70 */    CALL(sys_setreuid16)

        CALL(sys_setregid16)

        CALL(sys_sigsuspend_wrapper)

        CALL(sys_sigpending)

        CALL(sys_sethostname)

/* 75 */    CALL(sys_setrlimit)

        CALL(OBSOLETE(sys_old_getrlimit)) /* used by libc4 */

        CALL(sys_getrusage)

        CALL(sys_gettimeofday)

        CALL(sys_settimeofday)

/* 80 */    CALL(sys_getgroups16)

        CALL(sys_setgroups16)

        CALL(OBSOLETE(old_select))    /* used by libc4 */

        CALL(sys_symlink)

        CALL(sys_ni_syscall)        /* was sys_lstat */

/* 85 */    CALL(sys_readlink)

        CALL(sys_uselib)

        CALL(sys_swapon)

        CALL(sys_reboot)

        CALL(OBSOLETE(sys_old_readdir))    /* used by libc4 */

/* 90 */    CALL(OBSOLETE(old_mmap))    /* used by libc4 */

        CALL(sys_munmap)

        CALL(sys_truncate)

        CALL(sys_ftruncate)

        CALL(sys_fchmod)

/* 95 */    CALL(sys_fchown16)

        CALL(sys_getpriority)

        CALL(sys_setpriority)

        CALL(sys_ni_syscall)        /* was sys_profil */

        CALL(sys_statfs)

/* 100 */    CALL(sys_fstatfs)

        CALL(sys_ni_syscall)        /* sys_ioperm */

        CALL(OBSOLETE(ABI(sys_socketcall, sys_oabi_socketcall)))

        CALL(sys_syslog)

        CALL(sys_setitimer)

/* 105 */    CALL(sys_getitimer)

        CALL(sys_newstat)

        CALL(sys_newlstat)

        CALL(sys_newfstat)

        CALL(sys_ni_syscall)        /* was sys_uname */

/* 110 */    CALL(sys_ni_syscall)        /* was sys_iopl */

        CALL(sys_vhangup)

        CALL(sys_ni_syscall)

        CALL(OBSOLETE(sys_syscall))    /* call a syscall */

        CALL(sys_wait4)

/* 115 */    CALL(sys_swapoff)

        CALL(sys_sysinfo)

        CALL(OBSOLETE(ABI(sys_ipc, sys_oabi_ipc)))

        CALL(sys_fsync)

        CALL(sys_sigreturn_wrapper)

/* 120 */    CALL(sys_clone_wrapper)

        CALL(sys_setdomainname)

        CALL(sys_newuname)

        CALL(sys_ni_syscall)        /* modify_ldt */

        CALL(sys_adjtimex)

/* 125 */    CALL(sys_mprotect)

        CALL(sys_sigprocmask)

        CALL(sys_ni_syscall)        /* was sys_create_module */

        CALL(sys_init_module)

        CALL(sys_delete_module)

/* 130 */    CALL(sys_ni_syscall)        /* was sys_get_kernel_syms */

        CALL(sys_quotactl)

        CALL(sys_getpgid)

        CALL(sys_fchdir)

        CALL(sys_bdflush)

/* 135 */    CALL(sys_sysfs)

        CALL(sys_personality)

        CALL(sys_ni_syscall)        /* reserved for afs_syscall */

        CALL(sys_setfsuid16)

        CALL(sys_setfsgid16)

/* 140 */    CALL(sys_llseek)

        CALL(sys_getdents)

        CALL(sys_select)

        CALL(sys_flock)

        CALL(sys_msync)

/* 145 */    CALL(sys_readv)

        CALL(sys_writev)

        CALL(sys_getsid)

        CALL(sys_fdatasync)

        CALL(sys_sysctl)

/* 150 */    CALL(sys_mlock)

        CALL(sys_munlock)

        CALL(sys_mlockall)

        CALL(sys_munlockall)

        CALL(sys_sched_setparam)

/* 155 */    CALL(sys_sched_getparam)

        CALL(sys_sched_setscheduler)

        CALL(sys_sched_getscheduler)

        CALL(sys_sched_yield)

        CALL(sys_sched_get_priority_max)

/* 160 */    CALL(sys_sched_get_priority_min)

        CALL(sys_sched_rr_get_interval)

        CALL(sys_nanosleep)

        CALL(sys_arm_mremap)

        CALL(sys_setresuid16)

/* 165 */    CALL(sys_getresuid16)

        CALL(sys_ni_syscall)        /* vm86 */

        CALL(sys_ni_syscall)        /* was sys_query_module */

        CALL(sys_poll)

        CALL(sys_nfsservctl)

/* 170 */    CALL(sys_setresgid16)

        CALL(sys_getresgid16)

        CALL(sys_prctl)

        CALL(sys_rt_sigreturn_wrapper)

        CALL(sys_rt_sigaction)

/* 175 */    CALL(sys_rt_sigprocmask)

        CALL(sys_rt_sigpending)

        CALL(sys_rt_sigtimedwait)

        CALL(sys_rt_sigqueueinfo)

        CALL(sys_rt_sigsuspend_wrapper)

/* 180 */    CALL(ABI(sys_pread64, sys_oabi_pread64))

        CALL(ABI(sys_pwrite64, sys_oabi_pwrite64))

        CALL(sys_chown16)

        CALL(sys_getcwd)

        CALL(sys_capget)

/* 185 */    CALL(sys_capset)

        CALL(sys_sigaltstack_wrapper)

        CALL(sys_sendfile)

        CALL(sys_ni_syscall)        /* getpmsg */

        CALL(sys_ni_syscall)        /* putpmsg */

/* 190 */    CALL(sys_vfork_wrapper)

        CALL(sys_getrlimit)

        CALL(sys_mmap2)

        CALL(ABI(sys_truncate64, sys_oabi_truncate64))

        CALL(ABI(sys_ftruncate64, sys_oabi_ftruncate64))

/* 195 */    CALL(ABI(sys_stat64, sys_oabi_stat64))

        CALL(ABI(sys_lstat64, sys_oabi_lstat64))

        CALL(ABI(sys_fstat64, sys_oabi_fstat64))

        CALL(sys_lchown)

        CALL(sys_getuid)

/* 200 */    CALL(sys_getgid)

        CALL(sys_geteuid)

        CALL(sys_getegid)

        CALL(sys_setreuid)

        CALL(sys_setregid)

/* 205 */    CALL(sys_getgroups)

        CALL(sys_setgroups)

        CALL(sys_fchown)

        CALL(sys_setresuid)

        CALL(sys_getresuid)

/* 210 */    CALL(sys_setresgid)

        CALL(sys_getresgid)

        CALL(sys_chown)

        CALL(sys_setuid)

        CALL(sys_setgid)

/* 215 */    CALL(sys_setfsuid)

        CALL(sys_setfsgid)

        CALL(sys_getdents64)

        CALL(sys_pivot_root)

        CALL(sys_mincore)

/* 220 */    CALL(sys_madvise)

        CALL(ABI(sys_fcntl64, sys_oabi_fcntl64))

        CALL(sys_ni_syscall) /* TUX */

        CALL(sys_ni_syscall)

        CALL(sys_gettid)

/* 225 */    CALL(ABI(sys_readahead, sys_oabi_readahead))

        CALL(sys_setxattr)

        CALL(sys_lsetxattr)

        CALL(sys_fsetxattr)

        CALL(sys_getxattr)

/* 230 */    CALL(sys_lgetxattr)

        CALL(sys_fgetxattr)

        CALL(sys_listxattr)

        CALL(sys_llistxattr)

        CALL(sys_flistxattr)

/* 235 */    CALL(sys_removexattr)

        CALL(sys_lremovexattr)

        CALL(sys_fremovexattr)

        CALL(sys_tkill)

        CALL(sys_sendfile64)

/* 240 */    CALL(sys_futex)

        CALL(sys_sched_setaffinity)

        CALL(sys_sched_getaffinity)

        CALL(sys_io_setup)

        CALL(sys_io_destroy)

/* 245 */    CALL(sys_io_getevents)

        CALL(sys_io_submit)

        CALL(sys_io_cancel)

        CALL(sys_exit_group)

        CALL(sys_lookup_dcookie)

/* 250 */    CALL(sys_epoll_create)

        CALL(ABI(sys_epoll_ctl, sys_oabi_epoll_ctl))

        CALL(ABI(sys_epoll_wait, sys_oabi_epoll_wait))

        CALL(sys_remap_file_pages)

        CALL(sys_ni_syscall)    /* sys_set_thread_area */

/* 255 */    CALL(sys_ni_syscall)    /* sys_get_thread_area */

        CALL(sys_set_tid_address)

        CALL(sys_timer_create)

        CALL(sys_timer_settime)

        CALL(sys_timer_gettime)

/* 260 */    CALL(sys_timer_getoverrun)

        CALL(sys_timer_delete)

        CALL(sys_clock_settime)

        CALL(sys_clock_gettime)

        CALL(sys_clock_getres)

/* 265 */    CALL(sys_clock_nanosleep)

        CALL(sys_statfs64_wrapper)

        CALL(sys_fstatfs64_wrapper)

        CALL(sys_tgkill)

        CALL(sys_utimes)

/* 270 */    CALL(sys_arm_fadvise64_64)

        CALL(sys_pciconfig_iobase)

        CALL(sys_pciconfig_read)

        CALL(sys_pciconfig_write)

        CALL(sys_mq_open)

/* 275 */    CALL(sys_mq_unlink)

        CALL(sys_mq_timedsend)

        CALL(sys_mq_timedreceive)

        CALL(sys_mq_notify)

        CALL(sys_mq_getsetattr)

/* 280 */    CALL(sys_waitid)

        CALL(sys_socket)

        CALL(ABI(sys_bind, sys_oabi_bind))

        CALL(ABI(sys_connect, sys_oabi_connect))

        CALL(sys_listen)

/* 285 */    CALL(sys_accept)

        CALL(sys_getsockname)

        CALL(sys_getpeername)

        CALL(sys_socketpair)

        CALL(sys_send)

/* 290 */    CALL(ABI(sys_sendto, sys_oabi_sendto))

        CALL(sys_recv)

        CALL(sys_recvfrom)

        CALL(sys_shutdown)

        CALL(sys_setsockopt)

/* 295 */    CALL(sys_getsockopt)

        CALL(ABI(sys_sendmsg, sys_oabi_sendmsg))

        CALL(sys_recvmsg)

        CALL(ABI(sys_semop, sys_oabi_semop))

        CALL(sys_semget)

/* 300 */    CALL(sys_semctl)

        CALL(sys_msgsnd)

        CALL(sys_msgrcv)

        CALL(sys_msgget)

        CALL(sys_msgctl)

/* 305 */    CALL(sys_shmat)

        CALL(sys_shmdt)

        CALL(sys_shmget)

        CALL(sys_shmctl)

        CALL(sys_add_key)

/* 310 */    CALL(sys_request_key)

        CALL(sys_keyctl)

        CALL(ABI(sys_semtimedop, sys_oabi_semtimedop))

/* vserver */    CALL(sys_ni_syscall)

        CALL(sys_ioprio_set)

/* 315 */    CALL(sys_ioprio_get)

        CALL(sys_inotify_init)

        CALL(sys_inotify_add_watch)

        CALL(sys_inotify_rm_watch)

        CALL(sys_mbind)

/* 320 */    CALL(sys_get_mempolicy)

        CALL(sys_set_mempolicy)

        CALL(sys_openat)

        CALL(sys_mkdirat)

        CALL(sys_mknodat)

/* 325 */    CALL(sys_fchownat)

        CALL(sys_futimesat)

        CALL(ABI(sys_fstatat64,  sys_oabi_fstatat64))

        CALL(sys_unlinkat)

        CALL(sys_renameat)

/* 330 */    CALL(sys_linkat)

        CALL(sys_symlinkat)

        CALL(sys_readlinkat)

        CALL(sys_fchmodat)

        CALL(sys_faccessat)

/* 335 */    CALL(sys_ni_syscall)        /* eventually pselect6 */

        CALL(sys_ni_syscall)        /* eventually ppoll */

        CALL(sys_unshare)

        CALL(sys_set_robust_list)

        CALL(sys_get_robust_list)

/* 340 */    CALL(sys_splice)

        CALL(sys_sync_file_range2)

        CALL(sys_tee)

        CALL(sys_vmsplice)

        CALL(sys_move_pages)

/* 345 */    CALL(sys_getcpu)

        CALL(sys_ni_syscall)        /* eventually epoll_pwait */

        CALL(sys_kexec_load)

        CALL(sys_utimensat)

        CALL(sys_signalfd)

/* 350 */    CALL(sys_timerfd_create)

        CALL(sys_eventfd)

        CALL(sys_fallocate)

        CALL(sys_timerfd_settime)

        CALL(sys_timerfd_gettime)

/* 355 */    CALL(sys_signalfd4)

        CALL(sys_eventfd2)

        CALL(sys_epoll_create1)

        CALL(sys_dup3)

        CALL(sys_pipe2)

/* 360 */    CALL(sys_inotify_init1)

        CALL(sys_preadv)

        CALL(sys_pwritev)

#ifndef syscalls_counted

.equ syscalls_padding, ((NR_syscalls + ) & ~) - NR_syscalls

#define syscalls_counted

#endif

.rept syscalls_padding

        CALL(sys_ni_syscall)

.endr

calls.S

in arch/arm/kernel/entry-common.S  line102--106

    .equ NR_syscalls,

#define CALL(x) .equ NR_syscalls,NR_syscalls+1

#include "calls.S"

#undef CALL

#define CALL(x) .long x

2.第2次包含linux/arch/arm/kernel/calls.S，基于#define CALL(x) .long x。

in arch/arm/kernel/entry-common.S  line328--330

    .type    sys_call_table, #object

ENTRY(sys_call_table)

#include "calls.S"

在linux/arch/arm/kernel/entry_header.S中定义了几个特殊的寄存器变量，scno 用r7存储系统调用号 tbl 用r8存储系统调用表入口。

scno    .req    r7        @ syscall number

tbl    .req    r8        @ syscall table pointer

why    .req    r8        @ Linux syscall (!= )

tsk    .req    r9        @ current thread_info

swi异常处理函数中调用,tbl即r8中保存系统调用表的入口地址，

ENTRY(vector_swi)

    -->adr    tbl, sys_call_table        @ load syscall table pointer

sys_call_table即系统调用表入口地址，定义如下

    .type    sys_call_table, #object

ENTRY(sys_call_table)

#include "calls.S"

/*

此处calls.S展开如下：

.long sys_restart_syscall

.long sys_exit

.long sys_fork_wrapper

.long sys_read

.long sys_write

.long sys_open

......

*/

#undef ABI

#undef OBSOLETE

3.第3次包含linux/arch/arm/kernel/calls.S，基于#define CALL(x) .long x。构造sys_oabi_call_table

in arch/arm/kernel/entry-common.S  line477--479

    .type    sys_oabi_call_table, #object

ENTRY(sys_oabi_call_table)

#include "calls.S"

4.最终的系统调用

ENTRY(vector_swi)

    -->ldrcc    pc, [tbl, scno, lsl #]        @ call sys_* routine

最后的问题是系统调用表中的系统调用函数怎么定义的?这里以fs/open.c中的sys_open为例,概述系统调用函数的定义

SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, int, mode)

{

    long ret;

    if (force_o_largefile())

        flags |= O_LARGEFILE;

    ret = do_sys_open(AT_FDCWD, filename, flags, mode);

    /* avoid REGPARM breakage on x86: */

    asmlinkage_protect(, ret, filename, flags, mode);

    return ret;

}

SYSCALL_DEFINES宏定义如下：

SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, int, mode)

/*include/linux/syscalls.h*/

#define SYSCALL_DEFINE3(name, ...)          SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)

#define SYSCALL_DEFINEx(x, sname, ...)        __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)

#define __SYSCALL_DEFINEx(x, name, ...)        asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__))

#define __SC_DECL1(t1, a1)    t1 a1

#define __SC_DECL2(t2, a2, ...) t2 a2, __SC_DECL1(__VA_ARGS__)

#define __SC_DECL3(t3, a3, ...) t3 a3, __SC_DECL2(__VA_ARGS__)

#define __SC_DECL4(t4, a4, ...) t4 a4, __SC_DECL3(__VA_ARGS__)

#define __SC_DECL5(t5, a5, ...) t5 a5, __SC_DECL4(__VA_ARGS__)

#define __SC_DECL6(t6, a6, ...) t6 a6, __SC_DECL5(__VA_ARGS__)

按照以上的宏定义展开，最终为

asmlinkage long sys_open(const char __user * filename,int flags,int mode)

{

    long ret;

    if (force_o_largefile())

        flags |= O_LARGEFILE;

    ret = do_sys_open(AT_FDCWD, filename, flags, mode);

    /* avoid REGPARM breakage on x86: */

    asmlinkage_protect(, ret, filename, flags, mode);

    return ret;

}

5.简化的系统调用流程

    .align

ENTRY(vector_swi)

    /*1.入栈*/

    sub    sp, sp, #S_FRAME_SIZE

    stmia    sp, {r0 - r12}            @ Calling r0 - r12

    add    r8, sp, #S_PC

    stmdb    r8, {sp, lr}^            @ Calling sp, lr

    mrs    r8, spsr            @ called from non-FIQ mode, so ok.

    str    lr, [sp, #S_PC]            @ Save calling PC

    str    r8, [sp, #S_PSR]        @ Save CPSR

    str    r0, [sp, #S_OLD_R0]        @ Save OLD_R0

    zero_fp

    /*2.Get the system call number. */

    ldreq    r10, [lr, #-]            @ get SWI instruction

    enable_irq

    /*

     * If the swi argument is zero, this is an EABI call and we do nothing.

     *

     * If this is an old ABI call, get the syscall number into scno and

     * get the old ABI syscall table address.

     */

    bics    r10, r10, #0xff000000

    eorne    scno, r10, #__NR_OABI_SYSCALL_BASE  //

    /*3.系统调用函数指针数组*/

    ldrne    tbl, =sys_oabi_call_table

    stmdb    sp!, {r4, r5}            @ push fifth and sixth args

    cmp    scno, #NR_syscalls        @ check upper syscall limit

    /*swi异常处理返回*/

    adr    lr, ret_fast_syscall        @ return address

    /*4.跳转到具体的系统调用函数*/

    ldrcc    pc, [tbl, scno, lsl #]        @ call sys_* routine

ENDPROC(vector_swi)

6.swi异常返回

in arch/arm/kernel/entry-common.S

ret_fast_syscall:

 UNWIND(.fnstart    )

 UNWIND(.cantunwind    )

    disable_irq                @ disable interrupts

    ldr    r1, [tsk, #TI_FLAGS]

    tst    r1, #_TIF_WORK_MASK

    bne    fast_work_pending

    /* perform architecture specific actions before user return */

    arch_ret_to_user r1, lr

    @ fast_restore_user_regs

    ldr    r1, [sp, #S_OFF + S_PSR]    @ get calling cpsr

    ldr    lr, [sp, #S_OFF + S_PC]!    @ get pc

    msr    spsr_cxsf, r1            @ save in spsr_svc

    ldmdb    sp, {r1 - lr}^            @ get calling r1 - lr

    mov    r0, r0

    add    sp, sp, #S_FRAME_SIZE - S_PC

    movs    pc, lr                @ return & move spsr_svc into cpsr

 UNWIND(.fnend        )

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