How to debug problems in Linux kernel module `init()`?
- by Kimvais
I am using remote (k)gdb to debug a problem in a module that causes a panic when loaded e.g. when init() is called.
The stack trace just shows that do_one_initcall(mod->init) causes the crash. In order to get the symbol file loaded in the gdb, I need to get the address of the module text section, and to get that I need to get the module loaded.
Because the insmod in busybox (1.16.1) doesn't support -m so I'm stuck to grep modulename /proc/modules + adding the offset from nm to figure out the address.
So I'm facing a sort a of a chicken and an egg problem here - to be able to debug the module loading, I need to get the module loaded - but in order to get the module loaded, I need to debug the problem...
So I am currently thinking about two options - is there a way to get the address information either:
by printk() in the module init code
by printk() somewhere in the kernel code
all this prior to calling the mod->init() - so I could place a breakpoint there, load the symbol file, hit c and see it crash and burn...