Re: custom-kernel headers: scripts are wrong architecture

[Jan Kiszka <jan.kiszka@siemens.com>]

On 17.01.24 21:37, Moessbauer, Felix (T CED OES-DE) wrote:
> Dear devs,
> 
> while debugging a broken non-cross kernel module build, I found that
> there is a more generic issue about our linux-headers-${KERNEL_NAME}
> package: It might contain the kernel scripts (ELF binaries) in the
> wrong architecture. This only happens if the kernel itself is cross-
> compiled.
> 
> Let's consider the following example, where we compile for a debian
> bookworm arm64 target. We further look at the 'fixdeps' script from the
> kernel tools (required during kmod builds).
> 
> Example 1 (stock kernel):
> 
> The script is located in package linux-kbuild-6.1 (dependency of linux-
> headers-<...>).
> - file /usr/lib/linux-kbuild-6.1/scripts/basic/fixdep: ELF 64-bit LSB
> pie executable, ARM aarch64, ...
> - linux-headers-arm64 : arm64
> - linux-kbuild-6.1 : arm64
> 
> Example 2 (custom kernel):
> 
> - file /usr/src/linux-headers-6.1.54-cip6-rt3/scripts/basic/fixdep: ELF
> 64-bit LSB pie executable, x86-64
> - linux-headers-iot2050-rt : arm64
> 
> In example 2, the kmod build is obviously broken, as the emulated build
> will not be able to execute the x64 binary. Also, in an :arm64 package,
> there must be no foreign architecture binaries.
> 
> This behavior can also be reproduced, by cross-compiling a target with
> a custom kernel and disabling the cross-build for a module, using
> ISAR_CROSS_COMPILE="0" in the module build recipe.
> 
> It would be great, if someone could have a look there. At a first
> glance, this issue looks closely related to "linux-custom: Split up
> binaries from kernel headers to kbuild packages". Maybe Stefan can
> comment on this as well.

That is exactly what that patch is addressing. Stefan told me recently
that he rebased and refreshed that, and I hope we will see an update
soon. His aim is also resolving the issue that we currently build the
header and later on the kbuild package for the builder arch, rather than
for the target. But such an improvement needs more work as it requires
multiple kernel build runs for multiple archs while not all should
generate full kernels, obviously, only the needed kbuild packages.

Jan

> 
> PS: This bug was uncovered today, as the cross-build of a kernel module
> on debian bookworm arm64 is currently broken in upstream debian. I
> already reported this bug in [1].
> 
> [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1061075
> 
> Best regards,
> Felix
> 

-- 
Siemens AG, Technology
Linux Expert Center