The kmod tools, most importantly depmod are needed when cross-compiling a Linux kernel on macOS (Darwin). Currently depmod will just segfault and I diagnosed the problem as follows:

• all kmod tools are symlinked to one binary
• this binary uses basename(argv[0]) to determine its personality
• basename() requires the libgen.h header on Darwin, which is not included
• the return type is thus assumed to be int
• this causes the resulting char * (the actual return type) to be truncated to 32 bit
• depmod crashes

The fix is to include libgen.h at a prominent location so that all invocations of basename() are covered.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.