Thanks a lot for the answer!

It seems like using `KCONFIG_MODE = "--alldefconfig"` with
`KBUILD_DEFCONFIG = "msm8909_defconfig"` now ends up with the same kind of
errors as when I use the defconfig from the downstream kernel [1], i.e.:

```
| /tmp/ccz8jKgm.s: Assembler messages:
| /tmp/ccz8jKgm.s:985: Error: .err encountered
```

Could it be related to the tuning, e.g. I'm somehow defining a wrong
toolchain in my machine configuration [2] and it fails to build? I was
thinking about the tune-cortexa7.inc include, though it seems to me that
the apq8009 is a cortexa7 [3]:

> The Qualcomm Snapdragon 212 APQ8009 is an entry level SoC for Android
based tablets and smartphones. It contains four ARM Cortex-A7 CPU cores
(quad core)

[1]:
https://github.com/parrot-opensource/skycontroller3-opensource/blob/master/sources/linux-3.18.31/linux.config
[2]:
https://github.com/JonasVautherin/meta-skycontroller3/blob/main/conf/machine/skycontroller3.conf#L32
[3]:
https://www.notebookcheck.net/Qualcomm-Snapdragon-212-APQ8009-SoC-Benchmarks-and-Specs.169859.0.html

Best,

On Sat, Jan 23, 2021 at 11:06 AM Paul Barker <pbarker@konsulko.com> wrote:

> On Sat, 23 Jan 2021 at 02:29, Jonas Vautherin <jonas.vautherin@gmail.com>
> wrote:
> >
> > As a learning experience, I am trying to create a BSP for a device I own
> and whose downstream kernel is published. The device in question is the
> Parrot Skycontroller3, and the sources are available here.
> >
> > Let me start by sharing my issue. When I build the kernel with `bitbake
> virtual/kernel`, it fails with errors like:
> >
> > ```
> > |   AS      arch/arm/lib/backtrace.o
> > |   AS      arch/arm/lib/bswapsdi2.o
> > |   AS      arch/arm/lib/call_with_stack.o
> > | /tmp/ccz8jKgm.s: Assembler messages:
> > | /tmp/ccz8jKgm.s:985: Error: .err encountered
> > | /tmp/ccz8jKgm.s:1033: Error: .err encountered
> > | /tmp/ccz8jKgm.s:6812: Error: .err encountered
> > ```
> >
> > My layer is available here.
> >
> > I created it getting inspiration from meta-raspberrypi and meta-qti-bsp,
> which seems to have the same CPU: apq8009. According to the Parrot sources,
> my device runs a Qualcomm apq8009/msm89090 cpu. In my repo, I use as a
> defconfig file the linux.config that is available in the Parrot sources (I
> copied it in my kernel recipe under `files/defconfig` and added it to
> SRC_URI).
> >
> > The Parrot sources also refer to `LINUX_DEFAULT_CONFIG_TARGET :=
> msm8909_defconfig`, so I tried to set `KBUILD_DEFCONFIG =
> "msm8909_defconfig"`, but that is failing with different errors, such as:
> >
> > ```
> > error: 'VM_ARM_DMA_CONSISTENT' undeclared (first use in this function);
> did you mean 'DMA_ATTR_NON_CONSISTENT'?
> > ```
> >
> > or
> >
> > ```
> > error: 'L_PTE_YOUNG' undeclared
> > ```
> >
> > As a side note, their `drivers/Kconfig` seemed invalid, so I patched it.
> >
> > I am a bit lost now, not completely sure where my issues come from. I
> realize that changing the defconfig has quite some impact (I get different
> errors), and also that my machine configuration may be completely wrong (I
> am essentially guessing from the fact that it is an apq8009/msm8909, but
> for instance the tuning I just copied from meta-qti-bsp, which may be
> invalid).
> >
> > I would be glad if I could get hints about debugging this. Again, it is
> really a learning project: I would like to learn how to create a BSP from a
> downstream kernel.
>
> I think setting `KBUILD_DEFCONFIG = "msm8909_defconfig"` is likely the
> correct approach here. What you may be missing though is the correct
> value for KCONFIG_MODE. By default, the supplied defconfig file is
> copied to .config but dependencies between config options aren't
> resolved. You need to set `KCONFIG_MODE = "--alldefconfig"` to get the
> equivalent of `make msm8909_defconfig` to occur. See
>
> https://github.com/agherzan/meta-raspberrypi/blob/master/recipes-kernel/linux/linux-raspberrypi.inc#L19
> for an idea of how this is done for Raspberry Pi.
>
> Thanks,
>
> --
> Paul Barker
> Konsulko Group
>