Who may read this document?
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1. People who familiar with gdb but not never use kgdb
2. People who like to debug kernel or driver module using the gdb way.
Why to Using KGDB
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1. Want to debug kernel
2. Want to debug driver module
What’s hardware you needed to use KGDB
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1. Target system with have serial port
2. Host system with have serial port
3. Serial line
How to Debug Kernel using KGDB
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1. Download kgdb patch for your kernel at http://kgdb.linsyssoft.com/downloads
2. Host: cd /path/to/kernel/source/
3. Host: patch –p1 –i /path/to/patch/file
4. Host: make menuconfig, to confirm you choose kgdb support in KERNEL_HACKING
5. Host: make dep;make bzImage
6. Copy built bzImage to your target system.
7. Target: boot your target using the built bzImage with gdb gdbttyS=x gdbbaud=38400
you may add these parameters to your grub menu. Here ‘x’ is the index of your serial port used to connect your host such as 0,1 or 2.
8. Host: cd /path/to/kernel/source
9. Host: gdb vmlinux
10. Host gdb: set remotebaud 38400
11. Host gdb: target remote /dev/ttySx. Here ‘x’ is the index of your serial port used to connect your target.
How to Debug Driver Module using KGDB
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1. Host: build your driver module with –g option.
2. Copy your driver.o to your target system.
3. Reboot target with kernel build in kgdb.
4. Host gdb: Set breakpoint before kernel call module’s initialization function so we can debug module’s initialization function.
Kernel call module’s initialization in kernel/module.c: sys_init_module():mod->init().
5. Target: load your driver module using insmod and will stop at breakpoint set by 4.
6. Host gdb: p/x module_list
7. Host gdb: add-symbol-file /path/to/your/driver/module/sourcecode address
where address is the value of module_list+sizeof(module_list).
This command loads symbol file of your module so you can debug it.
8. As 7 have add the symbol file of your module, so you can set breakpoints to your source code such as module’s init function and enjoy the debugging.