module: nvidia: Unknown rela relocation: 4

[Andreas Beckmann]

I just managed to reproduce this error:

  # insmod /lib/modules/4.9.0-6-amd64/nvidia/nvidia-current.ko
  insmod: ERROR: could not insert module /lib/modules/4.9.0-6-amd64/nvidia/nvidia-current.ko: Invalid module format

with dmesg reporting

  module: nvidia: Unknown rela relocation: 4

since I wanted to try something with CUDA 9.2 (and therefore
driver 396.45).

The kernel headers were exactly matching the running kernel
(which is not the latest stable kernel due to some long-running
experiments on the machine) ... but the gcc-6 versions were different:
while stable has 6.3.0-18+deb9u1, I had 6.4.0-19 installed.

Building the module in a stretch chroot with gcc-6/stretch
produced a loadable variant of the module ...

Hopefully we remember to check the compiler version the next time
someone reports a similar spurious error :-)


Andreas