Hi all, I just tried compiling the latest wireguard-linux-compat kernel module v1.0.20211208 for kernel 4.4 [1] and encountered the following error: "net/wireguard/compat/siphash/siphash.c:112:36: error: ‘fallthrough’ undeclared (first use in this function)" The previous version v1.0.20210606 compiles and runs fine.
Some (inexpert) digging suggests that this is because a recent patch [2] modified siphash.c to use 'fallthrough', which is a Linux kernel compiler macro that was only added in kernel 5.4 [3]. In which case, presumably, either 'fallthrough' needs to be removed again, or the macro added in wireguard-linux-compat somewhere. I'm happy to submit a patch for either (although would appreciate some guidance if the second option), or someone with more experience can. In my immediate case, removing all instances of 'fallthrough' from siphash.c has fixed compilation. Thanks, Dan. [1] Specifically, in case this becomes relevant, cross-compiling for the Synology RT2600AC router (armv7l, kernel 4.4.60) from Ubuntu 20.04.4 x64 using gcc 4.9.3 according to the steps at https://gitlab.com/Kendek/syno-router-scripts/-/issues/3 [2] https://git.zx2c4.com/wireguard-linux-compat/commit/?id=ea6b8e7be5072553b37df4b0b8ee6e0a37134738 [3] https://github.com/torvalds/linux/commit/294f69e662d1570703e9b56e95be37a9fd3afba5
