Debian kernels >= 6.12 fail to build: headers force the `x86_64-linux-gnu-` toolchain prefix, builder images lack the prefixed binutils

[leogr]

Describe the bug

The kmod build fails for every Debian kernel >= 6.12 (trixie and newer), on both x86_64 and aarch64. The kernel headers of these kernels force a triplet-prefixed toolchain, and our builder images only ship the plain binutils names.

The .kernelvariables file shipped in linux-headers-6.12.107+deb13-amd64 has 👇

override CROSS_COMPILE = x86_64-linux-gnu-
CC = $(if $(DEBIAN_KERNEL_USE_CCACHE),$(CCACHE)) $(CROSS_COMPILE)gcc-14

driverkit overrides CC on the make command line, so the compiler is found. However, LD, OBJCOPY, NM, etc. are still derived from CROSS_COMPILE, and x86_64-linux-gnu-ld does not exist in falcosecurity/driverkit-builder:any-x86_64_gcc14.0.0-* (Fedora based, plain binutils). The configure step fails before compiling anything:

/bin/sh: line 1: x86_64-linux-gnu-ld: command not found
make[3]: *** [.../scripts/Makefile.build:430: /tmp/driver/build/driver/src/configure/0__SANITY/testmod.o] Error 127
[configure-kmod] Build system is broken, please see above errors
FATAL error executing driverkit
  └ err: Error response from daemon: Could not find the file /tmp/driver/build/driver/falco.ko in container ...

N.B. This is pre-existing and not related to a specific driver version: the same failure happens with 10.2.0+driver and 11.0.0+driver, and with driverkit v0.23.0 (the version pinned in the DBG jobs) as well as v0.23.2 (latest, identical to master). As a consequence, the Drivers Build Grid has never published a prebuilt kmod for Debian 13.

How to reproduce it

# debian-6.12.yaml
kernelversion: "1"
kernelrelease: 6.12.107-1-amd64
target: debian
architecture: amd64
output:
    module: output/falco_debian_6.12.107-1-amd64_1.ko
kernelurls:
    - http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-headers-6.12.107+deb13-amd64_6.12.107-1_amd64.deb
    - http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-headers-6.12.107+deb13-common_6.12.107-1_all.deb
    - http://security.debian.org/debian-security/pool/updates/main/l/linux/linux-kbuild-6.12.107+deb13_6.12.107-1_amd64.deb

driverkit docker -c debian-6.12.yaml --driverversion 11.0.0+driver --loglevel debug

Expected behaviour

The kmod builds, as it does for the other distros on the same kernel series.

Possible fixes

• add triplet-prefixed symlinks (x86_64-linux-gnu-ld, -objcopy, -nm, -strip, -ar, ... and the aarch64-linux-gnu- equivalents) to the builder-any-* images. IMO this is the least invasive option and fixes both arches
• alternatively, pass LD=ld OBJCOPY=objcopy NM=nm ... on the kmod make line, since those are plain assignments in the kernel Makefile (only CROSS_COMPILE is protected by override)

Either way, the fix needs a driverkit release, then the dbg-go pin and the DBG job image bumps.

Environment

• driverkit v0.23.2 (master) and v0.23.0
• builder image falcosecurity/driverkit-builder:any-x86_64_gcc14.0.0-2b04def
• Debian kernels 6.12.x, 6.16.x up to 7.1.x, both amd64 and arm64

Additional context

Since this is pre-existing, we agreed to postpone the fix after the Falco 0.45.0 release. Keeping this on hold for now 🙏

/kind bug
/area build