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This article will explain in detail how to debug the linux kernel module. The content of the article is of high quality, so the editor shares it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

1. Start the virtual machine and run it to kgdb: Waiting for connection from remote gdb

two。 Run on the host machine: socat tcp-listen:8888 / tmp/vbox2, where / tmp/vbox2 is the pipe file, which is the redirect destination file for the serial port of the target machine, and socat redirects the pipe file to port 8888 of tcp socket.

3. Open a new virtual terminal, cd path/to/kernel/source/tree, and execute gdb. / vmlinux

Output

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.

The target machine starts until you are prompted for a user name and password.

4. Enter the target machine, enter the user name and password (it is recommended to use the root user under the character interface), enter the g command, the target machine is cut off, and control is transferred to the gdb in the host machine. (add a line alias g='echo g > / proc/sysrq-trigger' to .bashrc in the user directory of the target machine root)

5. In the gdb in the host machine

(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. In the target machine

Insmod klogger2.ko

The target machine is cut off again, and control is transferred to the gdb in the host machine.

7. In the gdb in the host machine

[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)

You can debug your own LKM modules.

The initialization configuration file of gdb is attached ~ / .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_attrs- > attrs [$cur]-> name,mod- > sect_attrs- > attrs [$cur]-> address

Set $cur=$cur+1

End

End

Postscript: gdb debugging script is really difficult to write, simple string variable connection and equivalence judgment are very difficult, I do not know if my level is too poor or the script function of gdb is too weak, in short, kernel debugging is more difficult than Windbg.

On how to debug the linux kernel module to share here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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