1. 開啟虛擬機，虛擬機運行到 kgdb: Waiting for connection from remote gdb
2. 在Host機上運行： socat tcp-listen:8888 /tmp/vbox2, 其中/tmp/vbox2為管道文件,它是目標機串口的重定向目的文件，socat將這個管道文件又重定向到tcp socket的8888端口。
3. 開啟一個新的虛擬終端，cd path/to/kernel/source/tree, 然後執行gdb ./vmlinux
輸出
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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.
目標機會一直啟動，直到提示輸入用戶名密碼。
4. 進入目標機，輸入用戶名密碼(推薦使用字符界面下的root用戶)，輸入g命令，目標機被斷下，控制移交到Host機中的gdb中。(目標機root的用戶目錄中的.bashrc中添加一行alias g='echo g>/proc/sysrq-trigger')
5. 在Host機中的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. 在目標機中
insmod klogger2.ko
目標機再次斷下，控制權移交Host機中的gdb
7. 在Host機中的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)
你可以調試自己些的LKM模塊了
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
後記：gdb的調試腳本真難寫，簡單的字符串變量連接和等價判斷都顯得十分困難，不知道是我水平太差還是gdb的腳本功能太弱，總之比起Windbg來說，內核調試困難程度上了個等級