ARM系统调用
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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