building kernel modules for linux differnet version

[Saket Sinha]

On Tue, Mar 11, 2014 at 11:09 PM, Yann Droneaud <ydroneaud at opteya.com> wrote:
> Le mardi 11 mars 2014 à 22:42 +0530, Saket Sinha a écrit :
>> Please find my response inline
>>
>> >>          I have a scenario where I need to build a driver for
>> >> different kernel versions.
>> >> I have kernel-headers of different version in /lib/modules/
>> >> 2.6.32-xxxx
>> >> 2.6.39-xxxx
>> >>
>> >> and currently I am booted into 2.6.32-xxxx(which I find out by uname -r)
>> >>
>> >
>> > You don't need to boot on a specific kernel version to build external
>> > module for it.
>> >
>>
>> I am aware of that. I just need the kernel header of that specific
>> version instead.
>> What I meant was that since I was using the expression "uname -r" in
>> my makefile below-
>>  "make  -C   /lib/modules/$(shell uname -r)/build  M=$(PWD)  modules"
>> so I specified that.
>>
>> >> Now in my driver makefile, I generate .ko of driver
>> >> make  -C   /lib/modules/$(shell uname -r)/build  M=$(PWD)  modules
>> >>
>> >> but I notice that the driver .ko gets generated for 2.6.39-xxxx though
>> >> I am booted into  2.6.32-xxxx. Can anyone help me figure out why this
>> >> is happening?
>> >>
>> >
>> > Could you check that /lib/modules/2.6.32-xxxx/build is not a symbolic
>> > link to linux 2.6.39-xxxx sources ?
>>
>> I am pasting the output for you to check
>>
>> [root at Noi1-502156 ~]# cd /lib/modules
>> [root at Noi1-502156 modules]# ls
>> 2.6.32-220.4.2.el6.x86_64      2.6.39-300.17.1.el6uek.x86_64
>> 2.6.32-358.6.2.el6.x86_64      2.6.39-400.24.1.el6uek.x86_64
>> [root at Noi1-502156 modules]# ll
>> total 16
>> drwxr-xr-x. 8 root root 4096 Feb 28 14:41 2.6.32-220.4.2.el6.x86_64
>> drwxr-xr-x. 7 root root 4096 Jul 15  2013 2.6.32-358.6.2.el6.x86_64
>> drwxr-xr-x  8 root root 4096 Aug 12  2013 2.6.39-300.17.1.el6uek.x86_64
>> drwxr-xr-x. 4 root root 4096 Jul 10  2013 2.6.39-400.24.1.el6uek.x86_64
>> [root at Noi1-502156 modules]#
>>
>
> Now try "ls -dFl  /lib/modules/2.6.3*/build"

[root at Noi1-502156 ~]# ls -dFl  /lib/modules/2.6.3*/build
lrwxrwxrwx. 1 root root 50 Feb 17  2012
/lib/modules/2.6.32-220.4.2.el6.x86_64/build ->
../../../usr/src/kernels/2.6.32-220.4.2.el6.x86_64/
lrwxrwxrwx. 1 root root 50 Jun 11  2013
/lib/modules/2.6.32-358.6.2.el6.x86_64/build ->
../../../usr/src/kernels/2.6.32-358.6.2.el6.x86_64
lrwxrwxrwx  1 root root 54 Jul 10  2013
/lib/modules/2.6.39-300.17.1.el6uek.x86_64/build ->
../../../usr/src/kernels/2.6.39-300.17.1.el6uek.x86_64/

>
> And
>
> grep '^\(\(VERSION\)\|\(PATCHLEVEL\)\|\(SUBLEVEL\)\|\(EXTRAVERSION\)\|
> \(MAKEARGS\)\)' /lib/modules/*/build/Makefile
>

[root at Noi1-502156 ~]# grep
'^\(\(VERSION\)\|\(PATCHLEVEL\)\|\(SUBLEVEL\)\|\(EXTRAVERSION\)\|\(MAKEARGS\)\)'
/lib/modules/*/build/Makefile
/lib/modules/2.6.32-220.4.2.el6.x86_64/build/Makefile:VERSION = 2
/lib/modules/2.6.32-220.4.2.el6.x86_64/build/Makefile:PATCHLEVEL = 6
/lib/modules/2.6.32-220.4.2.el6.x86_64/build/Makefile:SUBLEVEL = 32
/lib/modules/2.6.32-220.4.2.el6.x86_64/build/Makefile:EXTRAVERSION =
-220.4.2.el6.x86_64
/lib/modules/2.6.39-300.17.1.el6uek.x86_64/build/Makefile:VERSION = 3
/lib/modules/2.6.39-300.17.1.el6uek.x86_64/build/Makefile:PATCHLEVEL = 0
/lib/modules/2.6.39-300.17.1.el6uek.x86_64/build/Makefile:SUBLEVEL = 36
/lib/modules/2.6.39-300.17.1.el6uek.x86_64/build/Makefile:EXTRAVERSION
= -300.17.1.el6uek.x86_64

> Check that matches the expected version.

As already mentioned, driver .ko gets generated for 2.6.39-xxxx.

Kindly let me know what you could make out of above outputs and why
exactly I am getting a   2.6.39-xxxx .ko file when I am specifying a
2.6.32-xxxx kernel header.

Regards,
Saket Sinha