本文主要是介绍arm linux vector_swi分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
linux 4.9 aarch32如下图中断、异常和系统调用的flow，中断一般是异步的硬件请求，异常通常是应用程序的错误触发，系统调用是应用程序对内核的功能请求
发生swi后进入系统中断向量然后执行vector_swi,源代码分析如下（CONFIG_AEABI）:
/*=============================================================================* SWI handler*-----------------------------------------------------------------------------*/
/*只保留一部分代码*/.align 5
ENTRY(vector_swi)sub sp, sp, #PT_REGS_SIZE stmia sp, {r0 - r12} @ Calling r0 - r12 ARM( add r8, sp, #S_PC ) ARM( stmdb r8, {sp, lr}^ ) @ Calling sp, lrTHUMB( mov r8, sp )THUMB( store_user_sp_lr r8, r10, S_SP ) @ calling sp, lrmrs r8, spsr @ called from non-FIQ mode, so ok.str lr, [sp, #S_PC] @ Save calling PCstr r8, [sp, #S_PSR] @ Save CPSRstr r0, [sp, #S_OLD_R0] @ Save OLD_R0zero_fpalignment_trap r10, ip, __cr_alignment /*对齐检查*/enable_irq /*使能中断*/ct_user_exitget_thread_info tsk /*进程的内核栈与thread_info放在相邻的两页*//** Get the system call number.*/uaccess_disable tbladr tbl, sys_call_table @ load syscall table pointerlocal_restart:ldr r10, [tsk, #TI_FLAGS] @ check for syscall tracingstmdb sp!, {r4, r5} @ push fifth and sixth argstst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls?bne __sys_tracecmp scno, #NR_syscalls @ check upper syscall limitbadr lr, ret_fast_syscall @ return address /*手动设置sys_*返回到ret_fast_syscall */ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine
/*Pure EABI user space always put syscall number into scno (r7). table是4字节对齐所以要用lsl把scno左移两位作table偏移,跳到对应的syscall 对应表项*/ENDPROC(vector_swi)执行sys_*函数后返回到ret_fast_syscall函数
/** This is the fast syscall return path. We do as little as possible here,* such as avoiding writing r0 to the stack. We only use this path if we* have tracing and context tracking disabled - the overheads from those* features make this path too inefficient.*/
ret_fast_syscall:UNWIND(.fnstart )UNWIND(.cantunwind )disable_irq_notrace @ disable interruptsldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracingtst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASKbne fast_work_pending /*检查是否有事情要做，比如signal处理 schedule处理等*//* perform architecture specific actions before user return */arch_ret_to_user r1, lr /*arch 相关返回用户空间要做的事*/restore_user_regs fast = 1, offset = S_OFF /*恢复用户空间现场，执行MOVS pc, lr时，CPSR会被SPSR覆盖，这条命令就cpu就恢复了user模式*/UNWIND(.fnend )
ENDPROC(ret_fast_syscall)/* Ok, we need to do extra processing, enter the slow path. */
fast_work_pending:str r0, [sp, #S_R0+S_OFF]! @ returned r0/* fall through to work_pending */tst r1, #_TIF_SYSCALL_WORKbne __sys_trace_return_nosave
slow_work_pending:mov r0, sp @ 'regs'mov r2, why @ 'syscall'bl do_work_pendingcmp r0, #0beq no_work_pendingmovlt scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE)ldmia sp, {r0 - r6} @ have to reload r0 - r6b local_restart @ ... and off we go
ENDPROC(ret_fast_syscall)system call 返回用户空间要做的事情_TIF_SYSCALL_WORK | _TIF_WORK_MASK 定义在thread_info.h中
/** thread information flags:* TIF_USEDFPU - FPU was used by this task this quantum (SMP)* TIF_POLLING_NRFLAG - true if poll_idle() is polling TIF_NEED_RESCHED*/
#define TIF_SIGPENDING 0 /* signal pending */
#define TIF_NEED_RESCHED 1 /* rescheduling necessary */
#define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
#define TIF_UPROBE 3 /* breakpointed or singlestepping */
#define TIF_SYSCALL_TRACE 4 /* syscall trace active */
#define TIF_SYSCALL_AUDIT 5 /* syscall auditing active */
#define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */
#define TIF_SECCOMP 7 /* seccomp syscall filtering active */#define TIF_NOHZ 12 /* in adaptive nohz mode */
#define TIF_USING_IWMMXT 17
#define TIF_MEMDIE 18 /* is terminating due to OOM killer */
#define TIF_RESTORE_SIGMASK 20#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_USING_IWMMXT (1 << TIF_USING_IWMMXT)/* Checks for any syscall work in entry-common.S */
#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP)/** Change these and you break ASM code in entry-common.S*/
#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \_TIF_NOTIFY_RESUME | _TIF_UPROBE)
以signal处理为例
do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
{/** The assembly code enters us with IRQs off, but it hasn't* informed the tracing code of that for efficiency reasons.* Update the trace code with the current status.*/trace_hardirqs_off();do {if (likely(thread_flags & _TIF_NEED_RESCHED)) {schedule(); /*schedule 当前进程出去*/} else {if (unlikely(!user_mode(regs)))return 0;local_irq_enable();if (thread_flags & _TIF_SIGPENDING) {int restart = do_signal(regs, syscall);/*处理当前进程挂起的信号*/if (unlikely(restart)) {/** Restart without handlers.* Deal with it without leaving* the kernel space.*/return restart;}syscall = 0;} else if (thread_flags & _TIF_UPROBE) {uprobe_notify_resume(regs);} else {clear_thread_flag(TIF_NOTIFY_RESUME);tracehook_notify_resume(regs);}}local_irq_disable();thread_flags = current_thread_info()->flags;} while (thread_flags & _TIF_WORK_MASK); /*事情做完才会继续返回用户空间*/return 0;
}
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