Linux系统内核分析实验——system_call中断处理过程

在linux中，当一个系统调用发生时，linux内核会做什么事？

linux system_call处理代码，该处理函数大量直接操作寄存器

ENTRY(system_call)    RING0_INT_FRAME         # can't unwind into user space anyway    ASM_CLAC    pushl_cfi %eax          # save orig_eax    SAVE_ALL    GET_THREAD_INFO(%ebp)                    # system call tracing in operation / emulation    testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)    jnz syscall_trace_entry    cmpl $(NR_syscalls), %eax    jae syscall_badsyssyscall_call:    call *sys_call_table(,%eax,4)syscall_after_call:    movl %eax,PT_EAX(%esp)      # store the return valuesyscall_exit:    LOCKDEP_SYS_EXIT    DISABLE_INTERRUPTS(CLBR_ANY)    # make sure we don't miss an interrupt                    # setting need_resched or sigpending                    # between sampling and the iret    TRACE_IRQS_OFF    movl TI_flags(%ebp), %ecx    testl $_TIF_ALLWORK_MASK, %ecx # current->work    jne syscall_exit_workrestore_all:    TRACE_IRQS_IRETrestore_all_notrace:#ifdef CONFIG_X86_ESPFIX32    movl PT_EFLAGS(%esp), %eax  # mix EFLAGS, SS and CS    # Warning: PT_OLDSS(%esp) contains the wrong/random values if we    # are returning to the kernel.    # See comments in process.c:copy_thread() for details.    movb PT_OLDSS(%esp), %ah    movb PT_CS(%esp), %al    andl $(X86_EFLAGS_VM | (SEGMENT_TI_MASK << 8) | SEGMENT_RPL_MASK), %eax    cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax    CFI_REMEMBER_STATE    je ldt_ss           # returning to user-space with LDT SS#endifrestore_nocheck:    RESTORE_REGS 4          # skip orig_eax/error_codeirq_return:    INTERRUPT_RETURN

大致流程：
1. 进入system_call
2. 保护现场SAVE_ALL
3. 根据eax中的调用号在系统调用表中调用相应功能
4. 存储返回值
5. 调用syscall_exit_work，进行中断检测与进程调度
6. 回复现场，返回用户态