Compiling for Windows on ARM

[satya-waylit]

I had an itch to get Wezterm native on my Windows arm64 machine. Here's what I had to do:

1. Open developer command prompt with arm64 toolchain selected
2. disable neon related files (see diff below). There may be way to do this with MSVC, but I figured I didn't need it.
3. Replace the opengl32.dll in assets/windows/mesa with the opengl32.dll available on my system at C:\Windows\System32\opengl32.dll
4. Otherwise I followed the build from source for Windows.

Hopefully this will be useful for eventual official Windows on arm binaries.

--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -7,3 +7,6 @@ ar = "x86_64-w64-mingw32-gcc-ar"
 # enabled for the target, so let's turn that on here.
 [target.x86_64-pc-windows-msvc]
 rustflags = ["-C", "target-feature=+crt-static"]
+
+[target.aarch64-pc-windows-msvc]
+rustflags = ["-C", "target-feature=+crt-static"]
diff --git a/assets/windows/mesa/opengl32.dll b/assets/windows/mesa/opengl32.dll
index 61cc5cf65..d1d299478 100644
Binary files a/assets/windows/mesa/opengl32.dll and b/assets/windows/mesa/opengl32.dll differ
diff --git a/deps/freetype/build.rs b/deps/freetype/build.rs
index 356ce0323..3c4578dfe 100644
--- a/deps/freetype/build.rs
+++ b/deps/freetype/build.rs
@@ -75,14 +75,17 @@ fn libpng() {
         .file("libpng/pngwutil.c");

     if let Ok(arch) = env::var("CARGO_CFG_TARGET_ARCH") {
-        match arch.as_str() {
+        let target = env::var("TARGET").unwrap();
+        if !target.contains("windows") {
+            match arch.as_str() {
             "aarch64" | "arm" => {
                 cfg.file("libpng/arm/arm_init.c")
-                    .file("libpng/arm/filter_neon.S")
-                    .file("libpng/arm/filter_neon_intrinsics.c")
-                    .file("libpng/arm/palette_neon_intrinsics.c");
+                .file("libpng/arm/filter_neon.S")
+                .file("libpng/arm/filter_neon_intrinsics.c")
+                .file("libpng/arm/palette_neon_intrinsics.c");
             }
             _ => {}
+            }
         }

[bogorad]

Thanks for writing this up. I used this as the starting point and got a native Windows 11 ARM64 build working locally.

What worked from your notes:

1. Built from an ARM64 Visual Studio developer environment.
2. Added crt-static for aarch64-pc-windows-msvc.
3. Skipped the libpng ARM NEON files on Windows.
4. Replaced assets/windows/mesa/opengl32.dll with C:\Windows\System32\opengl32.dll.

A couple of extra things were needed on my machine (Lenovo X13s):

• The first OpenSSL build failed because my environment had CC=clang and CXX=clang++. OpenSSL was being configured for
  MSVC, then invoking plain clang with MSVC-style flags like /Zi, /MT, and /Fo.... Forcing CC=cl and CXX=cl inside
  the ARM64 VS dev environment fixed that.

• The build completed, but the GUI did not actually start with the default OpenGL frontend. It exited with:

  Failed to create window: The OpenGL implementation is too old to work with glium
  
  

Running with WebGPU/DX12 worked:

wezterm.exe -n --config "front_end='WebGpu'" start --always-new-process --no-auto-connect -- cmd /c exit 0

I changed the default frontend to WebGpu only for windows + aarch64, leaving other targets on the existing OpenGL default.

• The bundled assets/windows/angle/libEGL.dll and libGLESv2.dll were x64. I replaced them with native ARM64 ANGLE DLLs from
  the installed ARM64 Chrome. That made the runtime bundle architecture-consistent.

Validation I ran:

cargo build --release
cargo test --release
target/release/wezterm.exe -n start --always-new-process --no-auto-connect -- cmd /c exit 0

I also checked the PE headers. The main executables are ARM64:

wezterm.exe IMAGE_FILE_MACHINE_ARM64
wezterm-gui.exe IMAGE_FILE_MACHINE_ARM64
wezterm-mux-server.exe IMAGE_FILE_MACHINE_ARM64
strip-ansi-escapes.exe IMAGE_FILE_MACHINE_ARM64

And the runtime graphics DLLs I replaced are ARM64 / ARM64X:

libEGL.dll IMAGE_FILE_MACHINE_ARM64
libGLESv2.dll IMAGE_FILE_MACHINE_ARM64
mesa/opengl32.dll IMAGE_FILE_MACHINE_ARM64X / ARM64EC

My fork with the working commit is here:

https://github.com/bogorad/wezterm

Commit:

bogorad@80c5e6eae