Hi All,

I got the linux kernel and LKM to get debugged using KGDB. To debug the module I use add-symbol-file with the virtual address where the module is loaded in target machine. But with this approach I am unable to debug the init module because the virtual address can be found only after the module is loaded.

So please can I know how to debug the init module?!?

Thanks.

You could try using printk at various levels or creating proc entry that gives you the relevant info.

You can do one thing. You put a break point at sys_init_module() function and
run the program step by step until you reach the following code in the sys_init_module().

/* Start the module */
if (mod->init != NULL)
ret = do_one_initcall(mod->init);

Before the if condition is executed, you can check the value of mod->init and load the symobol file like this in the gdb.

add-symbol-file <module.ko> 000000 -s .init.text <mod->init>

This only works for init. Please let me know if it works.

1 members found this post helpful.

@vedasolutions

Perfect works like a charm but with little modification.

I set a breakpoint at do_one_initcall function. The argument address was 0xe0892850 (in my case). Using objdump I found that my init module was 850 bytes away from the beginning of my text segment. Hence I loaded the symbol file as follows

add-symbol-file <module.ko> 0xe0892000

which allowed me to set a breakpoint to any of my module functions including init.

Thanks a lot!!!!