system_call中断处理过程分析

最新推荐文章于 2022-06-11 23:24:42 发布

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最新推荐文章于 2022-06-11 23:24:42 发布

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分类专栏： linux kernel

本文链接：https://blog.youkuaiyun.com/vincent_up/article/details/44893091

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本文通过一个具体的示例程序，深入分析了Linux内核中的系统调用机制，包括如何从用户空间进入内核空间、系统调用表的使用、系统调用的返回过程等关键技术细节。

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</pre><p></p><p><span style="color:rgb(51,51,51); font-family:'Microsoft YaHei'; font-size:14px; line-height:26px">张磊 + 原创作品转载请注明出处 + 《Linux内核分析》MOOC课程</span><a target=_blank target="_blank" href="http://mooc.study.163.com/course/USTC-1000029000" style="color:rgb(51,102,153); text-decoration:none; font-family:'Microsoft YaHei'; font-size:14px; line-height:26px">http://mooc.study.163.com/course/USTC-1000029000</a></p><p><span style="font-family:Microsoft YaHei; color:#333333"><span style="font-size:14px; line-height:26px">课程调用测试代码如下：</span></span></p><p><span style="font-family:Microsoft YaHei; color:#333333"><span style="font-size:14px; line-height:26px"></span></span></p><pre name="code" class="cpp">#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "menu.h"

#define FONTSIZE 10
int PrintMenuOS()
{
    int i, j;
    char data_M[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "  *    *  ",
        " ***  *** ",
        " * *  * * ",
        " * *  * * ",
        " *  **  * ",
        " *      * ",
        " *      * ",
        " *      * ",
        "          "
    };
    char data_e[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "          ",
        "    **    ",
        "   *  *   ",
        "  *    *  ",
        "  ******  ",
        "  *       ",
        "   *      ",
        "    ***   ",
        "          "
    };
    char data_n[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "          ",
        "    **    ",
        "   *  *   ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "          "
    };
    char data_u[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "          ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "  *    *  ",
        "   *  **  ",
        "    **  * ",
        "          "
    };
    char data_O[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "   ****   ",
        "  *    *  ",
        " *      * ",
        " *      * ",
        " *      * ",
        " *      * ",
        "  *    *  ",
        "   ****   ",
        "          "
    };
    char data_S[FONTSIZE][FONTSIZE] =
    {
        "          ",
        "    ****  ",
        "   **     ",
        "  **      ",
        "   ***    ",
        "     **   ",
        "      **  ",
        "     **   ",
        "  ****    ",
        "          "
    };

    for(i=0; i<FONTSIZE; i++)
    {
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_M[i][j]);
        }
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_e[i][j]);
        }
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_n[i][j]);
        }
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_u[i][j]);
        }
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_O[i][j]);
        }
        for(j=0; j<FONTSIZE; j++)
        {
            printf("%c", data_S[i][j]);
        }
        printf("\n");
    }
    return 0;
}

int Quit(int argc, char *argv[])
{
    /* add XXX clean ops */
}

int Time(int argc, char *argv[])
{
    time_t tt;
    struct tm *t;
    tt = time(NULL);
    t = localtime(&tt);
    printf("time:%d:%d:%d:%d:%d:%d\n",t->tm_year+1900, t->tm_mon, t->tm_mday, t->tm_hour, t->tm_min, t->tm_sec);
    return 0;
}

int TimeAsm(int argc, char *argv[])
{
    time_t tt;
    struct tm *t;
    asm volatile(
        "mov $0,%%ebx\n\t"
        "mov $0xd,%%eax\n\t" 
        "int $0x80\n\t" 
        "mov %%eax,%0\n\t"  
        : "=m" (tt) 
    );
    t = localtime(&tt);
    printf("time:%d:%d:%d:%d:%d:%d\n",t->tm_year+1900, t->tm_mon, t->tm_mday, t->tm_hour, t->tm_min, t->tm_sec);
    return 0;
}
int main()
{
    PrintMenuOS();
    SetPrompt("MenuOS>>");
    MenuConfig("version","MenuOS V1.0(Based on Linux 3.18.6)",NULL);
    MenuConfig("quit","Quit from MenuOS",Quit);
    MenuConfig("time","Show System Time",Time);
    MenuConfig("time-asm","Show System Time(asm)",TimeAsm);
    ExecuteMenu();
}

实验楼编译运行 gdb 调试程序：

1.rm menu -rf

2.git  clone https://github.com/mengning/menu.git

3.cd menu

4.make rootfs

库函数触发中断后，会进入一个ENTRY(system_call)函数中

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_badsys
syscall_call:
call *sys_call_table(,%eax,4)
syscall_after_call:
movl %eax,PT_EAX(%esp)		# store the return value
syscall_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_work

restore_all:
TRACE_IRQS_IRET
restore_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
#endif
restore_nocheck:
RESTORE_REGS 4			# skip orig_eax/error_code
irq_return:
INTERRUPT_RETURN
.section .fixup,"ax"

挑几个重要的分析下：

<pre name="code" class="cpp" style="color: rgb(51, 51, 51); font-size: 14px; line-height: 26px;">SAVE_ALL   //保存中断现场

movl %eax,PT_EAX(%esp)		# store the return value //调用系统函数

syscall_exit_work    //退出前返回状态

irq_return     //结束整个系统调用函数 返回。