如何进行linux内核模块调试

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1. 开启虚拟机，虚拟机运行到 kgdb: Waiting for connection from remote gdb

2. 在Host机上运行： socat tcp-listen:8888 /tmp/vbox2, 其中/tmp/vbox2为管道文件,它是目标机串口的重定向目的文件，socat将这个管道文件又重定向到tcp socket的8888端口。

3. 开启一个新的虚拟终端，cd path/to/kernel/source/tree, 然后执行gdb ./vmlinux

输出

GNU gdb 6.8-debian

Copyright (C) 2008 Free Software Foundation, Inc.

License GPLv3+: GNU GPL version 3 or later

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.  Type "show copying"

and "show warranty" for details.

This GDB was configured as "i486-linux-gnu"...

(gdb) set-remote

set remote baud rate to 115200c/s

set remote target to local tcp socket

kgdb_breakpoint () at kernel/kgdb.c:1721

1721        wmb(); /* Sync point after breakpoint */

(gdb) c

Continuing.

目标机会一直启动，直到提示输入用户名密码。

4. 进入目标机，输入用户名密码(推荐使用字符界面下的root用户)，输入g命令，目标机被断下，控制移交到Host机中的gdb中。(目标机root的用户目录中的.bashrc中添加一行alias g='echo g>/proc/sysrq-trigger')

5. 在Host机中的gdb中

(gdb) set-mod-break

set breakpoint in system module init function

Breakpoint 1 at 0xc014bac5: file kernel/module.c, line 2288.

(gdb) c

Continuing.

6. 在目标机中

insmod klogger2.ko

目标机再次断下，控制权移交Host机中的gdb

7. 在Host机中的gdb中

[New Thread 4693]

[Switching to Thread 4693]

Breakpoint 1, sys_init_module (umod=0x0, len=0, uargs=0x0)

at kernel/module.c:2288

2288        if (mod->init != NULL)

(gdb) print-mod-segment

Name:.note.gnu.build-id Address:0xdf977058

Name:.text Address:0xdf975000

Name:.rodata Address:0xdf977080

Name:.rodata.str1.4 Address:0xdf9774b4

Name:.rodata.str1.1 Address:0xdf977522

Name:.parainstructions Address:0xdf977a00

Name:.data Address:0xdf978440

Name:.gnu.linkonce.this_module Address:0xdf978480

Name:.bss Address:0xdf978a00

Name:.symtab Address:0xdf977a08

Name:.strtab Address:0xdf978078

(gdb) add-symbol-file /home/done/programs/linux-kernel/vlogger/klogger2.ko 0xdf975000 -s .data 0xdf978440 -s .bss 0xdf978a00

add symbol table from file "/home/done/programs/linux-kernel/vlogger/klogger2.ko" at

.text_addr = 0xdf975000

.data_addr = 0xdf978440

.bss_addr = 0xdf978a00

(y or n) y

Reading symbols from /home/done/programs/linux-kernel/vlogger/klogger2.ko...done.

(gdb) b hook_init

Breakpoint 2 at 0xdf976d19: file /home/done/programs/linux-kernel/vlogger/hook.c, line 255.

(gdb)

你可以调试自己些的LKM模块了

附gdb的初始化配置文件~/.gdbinit

define set-remote

echo set remote baud rate to 115200c/s\n

set remotebaud 115200

echo set remote target to local tcp socket\n

target remote tcp:localhost:8888

end

define set-mod-break

echo set breakpoint in system module init function\n

break kernel/module.c:2288

end

define print-mod-segment

set $sect_num=mod->sect_attrs->nsections

set $cur=0

while $cur < $sect_num

printf "Name:%-s Address:0x%x\n",mod->sect_attrs->attrs[$cur]->name,mod->sect_attrs->attrs[$cur]->address

set $cur=$cur+1

end

end

后记：gdb的调试脚本真难写，简单的字符串变量连接和等价判断都显得十分困难，不知道是我水平太差还是gdb的脚本功能太弱，总之比起Windbg来说，内核调试困难程度上了个等级。

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