CommonLibF4 Linux cross build

Builds a CommonLibF4 plugin on Linux. An F4SE plugin is a 64-bit Windows DLL that has to be built the way Microsoft's compiler builds it, even on Linux. So this is a cross build, which means the DLL is built on Linux for Windows. It uses clang-cl, a version of the clang compiler that works like Microsoft's, and F4SE then loads the DLL into Fallout 4 running under Proton.

Adding it to a plugin

A plugin laid out like the CommonLibF4 template adds this repository as a git submodule, which is a repository kept inside another one:

git submodule add https://github.com/hxef/commonlibf4-linux-cross.git contrib/linux-cross

Then the plugin's xmake.lua includes it right after CommonLibF4, and only when it builds on Linux:

-- include subprojects
includes("lib/commonlibf4")

if is_host("linux") then
    includes("contrib/linux-cross")
end

A Windows build never reads this repository, so it stays exactly like the template's build. A Linux build needs the submodule downloaded, which git clone --recurse-submodules does. Without it, xmake warns that includes("contrib/linux-cross") finds no files, and the build fails.

Setup

Install LLVM 19 or newer and make sure clang-cl, lld-link, llvm-ar and llvm-rc are on PATH. The Microsoft C++ standard library that xwin downloads stops the build with an error on an older clang.

Then download the Microsoft headers and libraries once with xwin. They are Microsoft's C and C++ standard libraries (the CRT) and the Windows SDK. --accept-license says that you accept the Visual Studio license they come with:

xwin --accept-license --arch x86_64 splat --output ~/.xwin

This fills ~/.xwin, the xwin folder. If you put it somewhere else, set XWIN_ROOT to that folder.

Building

From the plugin's top folder:

xmake f -p windows -a x64 -m releasedbg --toolchain=xwin-clang-cl
xmake build

Pass the same flags whenever you run xmake f again. Without them, xmake sets the build up for Linux instead.

What is in here

xmake.lua is the file the plugin includes. It loads the xwin-clang-cl toolchain and adds repo/ as a package repository, a folder where xmake looks for packages.

xwin-clang-cl.lua is the xwin-clang-cl toolchain, which tells xmake what compiler, linker and flags to use. It points clang-cl and lld-link at the Microsoft headers and libraries in the xwin folder, because xmake's own clang-cl toolchain looks for a Visual Studio install, which never exists on Linux.

repo/ holds 1 package, spdlog, which xmake uses in place of the one from xmake-repo, xmake's official package collection. CommonLibF4 needs spdlog as a compiled library. The xmake-repo package compiles it with cmake, and xmake's cmake support stops with an error whenever it builds for Windows and finds no Visual Studio:

-- xmake/modules/package/tools/cmake.lua
local msvc = package:toolchain("msvc")
assert(msvc:check(), "vs not found!")

Linux never has Visual Studio, so this check always fails there. Using spdlog as header only, where all of its code sits in the header files, does not work either. In that mode, spdlog's os.h includes os-inl.h, which includes <windows.h>. That file defines MAX_PATH and ERROR as macros, which are names the compiler swaps for a value before it reads the code. They break REX::W32::MAX_PATH and REX::ERROR all over CommonLibF4.

So the spdlog package in repo/ compiles spdlog's few source files with xmake instead of cmake. It is adapted from the spdlog package of xmake-repo, and its versions, options and defines match that package.

License

Apache-2.0, the same license as xmake-repo, because the spdlog package in repo/ is adapted from xmake-repo's. See LICENSE and NOTICE.