HOSTCC set incorrectly for x86-64 environments

[AmrikSadhra]

Hey folks,

I was bumping into issues compiling the kernel on x86-64, using the Dev Container plugin in VSCode as specified in your docs:

make -C "src" -j16 ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTCC=aarch64-linux-gnu-gcc KDEB_COMPRESS="xz" KDEB_CHANGELOG_DIST="unstable" DPKG_FLAGS=-d LOCALVERSION=-3-qcom KERNELRELEASE=6.17.1-3-qcom KDEB_PKGVERSION=6.17.1-3 defconfig qcom_module_defconfig radxa.config radxa_custom.config
make[2]: Entering directory '/workspaces/linux-qcom/src'
HOSTCC scripts/basic/fixdep
/bin/sh: 1: ./scripts/basic/fixdep: Exec format error
make[5]: *** [scripts/Makefile.host:114: scripts/basic/fixdep] Error 126
make[5]: *** Deleting file 'scripts/basic/fixdep'
make[4]: *** [Makefile:655: scripts_basic] Error 2
make[3]: *** [/workspaces/linux-qcom/src/Makefile:369: __build_one_by_one] Error 2
make[2]: *** [Makefile:248: __sub-make] Error 2
make[2]: Leaving directory '/workspaces/linux-qcom/src'
make[1]: *** [Makefile.extra:32: build-defconfig] Error 2
make[1]: Leaving directory '/workspaces/linux-qcom'
dh_auto_build: error: make -j1 "INSTALL=install --strip-program=true" returned exit code 2
make: *** [debian/rules:12: build] Error 25
dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2
debuild: fatal error at line 1182:
dpkg-buildpackage -us -uc -ui -b failed
make: *** [Makefile:103: debuild] Error 29

The problem seems to be HOSTCC=aarch64-linux-gnu-gcc:

linux-qcom/Makefile.extra

Line 16 in 1409513

ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) HOSTCC=$(CROSS_COMPILE)gcc \

I believe we're telling the build system to compile host tools (like fixdep) with the ARM64 cross-compiler. I was under the impression that host tools need to run on the build machine (which for me is x86_64) and not the target. Patching HOSTCC to just "gcc" seems to have resolved things. Perhaps this wasn't hit as you compile from an Arm64 host directly? Equally likely I'm just doing something wrong.

[csvke]

Yes, I can confirm the issue. Perhaps someone used an aarch64 to compile, so the error went unnoticed, especially the Radxa documentation explicitly mentioned in their documentation to use x86_64.

Could also be an unintentional bug or misconfiguration in rsdk infra-package-update as the Makefile.extra is generated through rsdk infra-package-update

@RadxaYuntian you may want to have a look.

[RadxaYuntian]

First, don't feed stuff to ChatGPT.

Second, Linux will copy host tools to the final kernel header package, even when you are cross compiling. This results in broken header package as it contains x86_64 binary in arm64 header. Instead of seeing fixdep error on your build machine, you now see this error on your target machine.

This is a long standing issue as described here (p66), that you either have to native build on ARM64, or cross build but set HOSTCC to build ARM64 binaries. I'm not aware if the situation changed recently, but after we retool our build infrastructure it has been working fine.

You can see this exact issue biting our competitor's product:

And here is the kernel header from this repo, cross compiled on x86_64 machine with GitHub public runner:

---

I will admit that the documentation currently did not do a good job to point this out. You need to set up binfmt and qemu-user-static to run ARM64 binaries on x86_64 machines, and it is easy to overlook this if you have configured it before, which is probably what happened when my team was writing the build documentation.

Since we already have a central documentation site, I did not include enough documentation in the repo, especially for Linux repos under radxa-pkg, where majority uses the same boilerplate structure.

You can see here for how to configure Debian to use qemu-user-static to build with devcontainer. I'll also see how the documentation can be improved on this area.