[System] Wrong compiler version when building extra (out-of-tree) kernel module

[martinb]

Hi all,

I've just made a fresh installation of Kubuntu 25.04, installed gcc as well as linux-headers-$(uname -r) but when I try to build an out-of-tree kernel module, I get this error

warning: the compiler differs from the one used to build the kernel
The kernel was built by: x86_64-linux-gnu-gcc-14 (Ubuntu 14.2.0-19ubuntu2) 14.2.0
You are using: gcc-14 (Ubuntu 14.2.0-19ubuntu2) 14.2.0​

I've seen such errors before if e.g. the kernel was built with gcc-10 and I tried to build a module with gcc-11, but this case looks different because obviously, the compiler versions are identical (gcc-14 (Ubuntu 14.2.0-19ubuntu2) 14.2.0) and it looks like the kernel was simply built using a kind of cross compiler which is effectively the same as the native compiler.

If someone wants to duplicate this, just build the "devel" branch of this git repo:
https://git.meinbergglobal.com/drivers/mbgtools-lx.git/

How can this be fixed?

Martin