kernel plugin: pick the correct kernel-image-target per architecture

[Paolo Pisati]

Different kernel architecture needs different kernel-image-target:

ARCH=arm:
...
Architecture specific targets (arm):
* zImage - Compressed kernel image (arch/arm/boot/zImage)
  Image - Uncompressed kernel image (arch/arm/boot/Image)
...

ARCH=arm64:
...
Architecture specific targets (arm64):
* Image.gz - Compressed kernel image (arch/arm64/boot/Image.gz)
  Image - Uncompressed kernel image (arch/arm64/boot/Image)
...

ARCH=powerpc:
...
Architecture specific targets (powerpc):
* zImage - Build default images selected by kernel config
  zImage.* - Compressed kernel image (arch/powerpc/boot/zImage.*)
...

etcetc

At the moment snapcraft.yaml::kernel-image-target could be only a string, and to support compiling the kernel for different architectures from the same snapcraft.yaml, we need a dynamic mechanism - either an internal mapping in snapcraft:

case ARCH:
 amd64)
  target=bzImage
 arm)
  target=zImage
 arm64)
  target=Image
...
etcetc
...
esac

or a callback mechanism (as we exploited in kdefconfig to support multiple archs/configs):

...
kdefconfig: ['--makefile=debian/snapcraft.mk', 'branch=master','flavour=generic', 'config']
...

$ cat debian/snapcraft.mk
ifeq ($(ARCH),)
  arch := $(shell uname -m | sed -e s/i.86/i386/ -e s/x86_64/amd64/ \
            -e s/arm.*/armhf/ -e s/s390/s390x/ -e s/ppc.*/powerpc/ \
            -e s/aarch64.*/arm64/ )
else ifeq ($(ARCH),arm)
  arch := armhf
else
  arch := $(ARCH)
endif
config:
        cat debian.$(branch)/config/config.common.ubuntu debian.$(branch)/config/$(arch)/config.common.$(arch) debian.$(branch)/config/$(arch)/config.flavour.$(flavour) >.config

The entire snapcraft.yaml that we would like to ship with the generic Ubuntu kernel, is attached below.

[Sergio Schvezov (sergiusens)]

https://github.com/snapcore/snapcraft/pull/689

[Paolo Pisati (p-pisati)]

With this patch i was able to snap, from the same kernel tree, kernels for amd64, arm64 and armhf - looks good.