line numbers in debugging kernel module

Hello,
I build kernel module with these line in Makefile:
CFLAGS:=$(CFLAGS) -DDEBUG -DMKDEBUG=yes -DMKCTF=yes -Wno-multichar -O0 -g

and when I loaded crash dump into gdb and use
add-symbol-file path_to_module.kmod <address of .text>

then after bt I see function names but not line numbers.
I tried to switch off CTF with -DMKCTF=no, add -gdwarf-4 and another 
variants, still I have no line numbers and I dont see section named .debug.
when I use compiler switch -v still I am seeing that ctfconvert is 
called on every compiled object file.

How to change Makefile to see line numbers in gdb ?