[yocto] Q on how to keep the debug information for kernel module

[John Rama]

Dear Yocto specialists

I have one question. 
When building the kernel module and install to rootfs with Yocto, I got the kernel module without debug information.
Investigating a little bit revealed that it seems do_package process remove the debug information from binary, 
as the file size indicates as shown below.

-rw-r--r-- 1 atmark atmark    321 12月 14 17:15 ./3.14.28-r0/git/drivers/net/usb/.usbnet.ko.cmd
-rw-r--r-- 1 atmark atmark 278101 12月 14 17:15 ./3.14.28-r0/git/drivers/net/usb/usbnet.ko
-rw-r--r-- 1 atmark atmark 278101 12月 14 20:08 ./3.14.28-r0/image/lib/modules/3.14.28-rt25-1.0.0_ga-avb_1_0_0+g91cf351/kernel/drivers/net/usb/usbnet.ko
-rw-r--r-- 2 atmark atmark  45328 12月 14 20:08 ./3.14.28-r0/package/lib/modules/3.14.28-rt25-1.0.0_ga-avb_1_0_0+g91cf351/kernel/drivers/net/usb/usbnet.ko
-rw-r--r-- 2 atmark atmark  45328 12月 14 20:08 ./3.14.28-r0/packages-split/kernel-module-usbnet/lib/modules/3.14.28-rt25-1.0.0_ga-avb_1_0_0+g91cf351/kernel/drivers/net/usb/usbnet.ko

I would like to kept debug information preserved.
I've check the manual but could not find out how to control this behavior.

Does anyone know how to do that ?
Any information is highly appreciated.

Kind Regars,
John Rama