GNU/Linux Tips
来自Jack's Lab
1 Mounting partition from VDI image
$ od -j344 -N4 -td4 /work/FreeDos.vdi | awk 'NR==1{print $2;}' 8192 $ sudo losetup -f --show -o 8192 /work/FreeDos.vdi /dev/loop0 $ sudo fdisk -lu /dev/loop0 Disk /dev/loop0: 113 MB, 113246208 bytes 16 heads, 63 sectors/track, 219 cylinders, total 221184 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Device Boot Start End Blocks Id System /dev/loop0p1 * 63 1023119 511528+ 6 FAT16 $ sudo mount -o loop,offset=$((512*63)) /dev/loop0 /mnt $ ls /mnt/ AUTOEXEC.BAT BOOTSECT.BIN COMMAND.COM FDCONFIG.SYS FDOS KERNEL.SYS $ sudo umount /mnt $ sudo losetup -d /dev/loop0 $ VBoxManage clonehd /work/FreeDos.vdi /work/freedos.vdi --format VDI --variant Fixe
2 GDB Tips
1. 查看寄存器
(gdb) i r (gdb) i r a # 查看所有寄存器(包括浮点、多媒体) (gdb) i r esp (gdb) i r pc
2. 查看内存
(gdb) x /wx 0x80040000 # 以16进制显示指定地址处的数据 (gdb) x /8x $esp (gdb) x /16x $esp+12 (gdb) x /16s 0x86468700 # 以字符串形式显示指定地址处的数据 (gdb) x /24i 0x8048a51 # 以指令形式显示指定地址处的数据(24条)
3. 修改寄存器的值
(gdb) set $v0 = 0x004000000 (gdb) set $epc = 0xbfc00000
4. 修改内存的值
(gdb) set {unsigned int}0x8048a51=0x0 (gdb) set *(unsigned int*)0x8048a54=0x55aa55aa
5. 内存搜索
Usage: find <start> <end> <count> <value> (gdb) define find set $ptr = $arg0 set $cnt = 0 while ( ($ptr<=$arg1) && ($cnt<$arg2) ) if ( *(unsigned int *)$ptr == $arg3 ) x /wx $ptr set $cnt = $cnt + 1 end set $ptr = $ptr + 4 end end
6. 断点、监测点
(gdb) b *0x80400000 (gdb) watch *(unsigned int *)0xbffff400==0x90909090