[yocto] Building kernel backports for ARM with Yocto

[Darcy Watkins]

I tried building backports under Yocto a few years back using Yocto daisy branch with kernel 3.4 for x86 and kernel 3.12 for ARM.  After a fair amount of pain I was able to get it to sort of work.  The problem was mainly a sysroot arm-wrestle between kernel and backports because they both generate the same kernel module packages.  It was a last-one-wins arm-wrestle.  It sort of worked OK with daisy branch, but newer yocto versions have stricter management of sysroots and staging areas.

I think what we need is some sort of virtual provider or alternatives scheme to make this work properly.

You can also run into problems related to exports to other out-of-tree modules but IIRC, it would only affect an out-of-tree module with an incompatible license.

I was able to run a few circa kernel 3.18 backports experimentally on a kernel 3.4 and a kernel 3.12.  Eventually we just upgraded the kernel.  Another project I know of used backports to update their kernel source and then created a recipe to build kernel from that source.

The notes/questions I had in the end were:


  *   was building backports as out-of-tree kernel modules
  *   was concerned that this wouldn’t provide updated kernel staging source, particularly with respect to any updated includes
  *   wasn’t sure what would be propagated into the sysroot
  *   should consider the backports use case that patches the kernel source and then perhaps use this to generate patchset to be added to kernel recipe (bbappend)
  *   otherwise need to ensure proper handling of sysroot, staging, (as well as a notion of providers and/or alternatives like I mentioned earlier)

I haven’t touched this in years, but perhaps it may help a bit.

I think your best bet for short term is to use it to patch the kernel and then capture the changes as a patchset to add to a kernel recipe.



Regards,

Darcy

Darcy Watkins ::  Senior Staff Engineer, Firmware

SIERRA WIRELESS
Direct  +1 604 233 7989   ::  Fax  +1 604 231 1109  ::  Main  +1 604 231 1100
13811 Wireless Way  :: Richmond, BC Canada V6V 3A4
[P2]
dwatkins at sierrawireless.com<mailto:dwatkins at sierrawireless.com> :: www.sierrawireless.com<http://www.sierrawireless.com/>

From: yocto-bounces at yoctoproject.org [mailto:yocto-bounces at yoctoproject.org] On Behalf Of Marlon Smith
Sent: October-18-17 3:14 PM
To: yocto at yoctoproject.org
Subject: [yocto] Building kernel backports for ARM with Yocto

Hi everyone,

I'm trying to build the Linux backports project to get updated wifi drivers on an older kernel.  The problem is that when building backports, it first builds several tools that need to be run natively before cross-compiling the rest of the project.

I know how to write a bitbake recipe to compile natively, and how to write one to build for the target, but I can't figure out how to combine the two.  The backports project has steps for LTIB:


 %Build

 export PATH=$UNSPOOF_PATH



 make menuconfig prefix=%{_prefix} \

   CROSS_COMPILE=${TOOLCHAIN_PATH}/bin/${TOOLCHAIN_PREFIX} \

   ARCH=$LINTARCH KLIB=${TOP}/rootfs/lib/modules/%{kversion} \

   KLIB_BUILD=${TOP}/rpm/BUILD/linux



 export PATH=$SPOOF_PATH



 make prefix=%{_prefix} \

   CROSS_COMPILE=${TOOLCHAIN_PATH}/bin/${TOOLCHAIN_PREFIX} \

   ARCH=$LINTARCH KLIB=${TOP}/rootfs/lib/modules/%{kversion} \

   KLIB_BUILD=${TOP}/rpm/BUILD/linux



I believe what I need is an equivalent to the line export PATH=$UNSPOOF_PATH but I can't find anything in the Yocto documentation or mailing lists that would be equivalent to that.



Any help would be much appreciated!



Thanks



Marlon
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.yoctoproject.org/pipermail/yocto/attachments/20171018/adef7e60/attachment.html>