[yocto] Building kernel backports for ARM with Yocto

[Marlon Smith]

Darcy, thanks for the detailed reply!
Do you remember how you were able to get it to compile in the first
place?  I end up with this error:
./kconf/conf: 1: ./kconf/conf: Syntax error: word unexpected (expecting
")")
..because backports needs to compile conf for x86_64, but instead
compiles it for ARM.  Once that step is done, it needs to compile the
rest of the project for ARM, but this error stops it.
I think I could work around the sysroot arm-wrestle because of the way
our project is built, but haven't made it to that point yet.
Here's the bb file I'm using:
---------------------------
include backports.inc
SRCBRANCH = "linux-4.2.y"
LOCALVERSION = "v4.2.6-1-0-g90118c7"
SRCREV = "90118c7656bb55243620c9dc9cc3f12582b1807f"
DEPENDS += "linux-myproject"do_configure_prepend() {
	export CROSS_COMPILE=${TARGET_PREFIX}
	export ARCH=${TARGET_ARCH}
	export KLIB_BUILD=${STAGING_KERNEL_DIR}
	export KLIB=${STAGING_DIR_TARGET}
	make
}
-----------------------------------
On Wed, 2017-10-18 at 22:53 +0000, Darcy Watkins wrote:
> 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
>  
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>  
> From: yocto-bounces at yoctoproject.org [mailto:yocto-bounces at yoctoproje
> ct.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
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