反汇编调试

在linux环境下编写at24c02的驱动程序时，出现segmentation fault的错误提示，具体提示如下图

从后往前看发现调用关系是sys_ioctl->do_vfs_ioctl->at24c02_ioctl，将问题定位至at24c02_ioctl函数处，该函数源码如下，该函数被at24c02_drv.c文件包含，生成的驱动文件是at24c02_drv.ko

static long at24c02_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	unsigned char addr;
	unsigned char data;
	unsigned int ker_buf[2];
	unsigned int *usr_buf = (unsigned int *)arg;
	unsigned char byte_buf[2];
	
	struct i2c_msg msgs[2];

	copy_from_user(ker_buf, usr_buf, 8);

	addr = ker_buf[0];
	
	switch (cmd)
	{
		case IOC_AT24C02_READ:
		{
			/* 璇籄T24C02 */
			msgs[0].addr  = at24c02_client.addr;
			msgs[0].flags = 0; /* 鍐?*/
			msgs[0].len   = 1;
			msgs[0].buf   = &addr;

			msgs[1].addr  = at24c02_client.addr;
			msgs[1].flags = I2C_M_RD; /* 璇?*/
			msgs[1].len   = 1;
			msgs[1].buf   = &data;
		
			i2c_transfer(at24c02_client->adapter, msgs, 2);

			ker_buf[1] = data;
			copy_from_user(usr_buf, ker_buf, 8);
			
			break;
		}
		case IOC_AT24C02_WRITE:
		{
			/* 鍐橝T24C02 */
			byte_buf[0] = addr;
			byte_buf[1] = ker_buf[1];
			
			msgs[0].addr  = at24c02_client.addr;
			msgs[0].flags = 0; /* 鍐?*/
			msgs[0].len   = 2;
			msgs[0].buf   = byte_buf;

			i2c_transfer(at24c02_client->adapter, msgs, 1);

			mdelay(20);
			
			break;
		}
	}
}

想要定位问题现将驱动文件反汇编，具体命令是arm-linux-objdump -D at24c02_drv.ko > at24c02.dis，再使用vim at24c02.dis查看具体内容，在反汇编文件中直接查找at24c02_ioctl,发现起始机器码是0074，图一中LR指向ioctl+0x1dc,则0x74+0x1dc=250,说明错误发生处是机器码为250的地方，

结合250上下处的汇编语句，判断copy_from_user使用错误，应该为copy_to_user