[WireGuard] Error building against grsec-enabled kernel

[Toke Høiland-Jørgensen]

Toke Høiland-Jørgensen <toke at toke.dk> writes:

> I'm getting build errors when building WireGuard against a grsec-enabled
> kernel (on Arch linux):
>
> DKMS make.log for wireguard-0.0.20161014 for kernel 4.7.8.201610161720-1-grsec (x86_64)
> Wed 19 Oct 14:59:25 CEST 2016
> make: Entering directory '/usr/lib/modules/4.7.8.201610161720-1-grsec/build'
>   LD      /var/lib/dkms/wireguard/0.0.20161014/build/built-in.o
>   CC [M]  /var/lib/dkms/wireguard/0.0.20161014/build/main.o
> /var/lib/dkms/wireguard/0.0.20161014/build/main.o: warning: objtool: mod_exit(): can't find starting instruction
>   CC [M]  /var/lib/dkms/wireguard/0.0.20161014/build/noise.o
>   CC [M]  /var/lib/dkms/wireguard/0.0.20161014/build/device.o
> /var/lib/dkms/wireguard/0.0.20161014/build/device.c:330:29: error: constified variable ‘link_ops’ placed into writable section ".data..read_mostly"
>  static struct rtnl_link_ops link_ops __read_mostly = {
>                              ^~~~~~~~
> make[1]: *** [scripts/Makefile.build:290: /var/lib/dkms/wireguard/0.0.20161014/build/device.o] Error 1
> make: *** [Makefile:1465: _module_/var/lib/dkms/wireguard/0.0.20161014/build] Error 2
> make: Leaving directory '/usr/lib/modules/4.7.8.201610161720-1-grsec/build'
>
> Any idea how to fix this?

OK, so turns out just getting rid of the __read_mostly fixes things.
This could conceivably be conditioned on CONSTIFY_PLUGIN in the upstream
source? :)

-Toke