INSTALL-LLVM.md

Installing LLVM for ARM64 Windows Builds

Why LLVM is Needed

Some Rust dependencies (like ring, a cryptography library) require LLVM/Clang to build on ARM64 Windows. This is because they contain assembly code or use build tools that depend on Clang.

Installation Options

Option 1: Install LLVM via winget (Recommended - Easiest)

# Install LLVM using Windows Package Manager
winget install LLVM.LLVM

After installation:

1. Restart your terminal
2. Verify installation:

   clang --version

Option 2: Install LLVM Manually

1. Download LLVM from: https://github.com/llvm/llvm-project/releases

2. Get the latest ARM64 Windows installer (e.g., LLVM-<version>-win-arm64.exe)

3. Run the installer

4. Important: During installation, check "Add LLVM to the system PATH"

5. Restart your terminal

6. Verify:

   clang --version

Option 3: Install via Chocolatey

# Install using Chocolatey (if you have it installed)
choco install llvm

Verify Installation

After installing LLVM, verify that clang is available:

Get-Command clang
clang --version

You should see output like:

clang version 18.1.8
Target: aarch64-pc-windows-msvc
...

Build After Installation

Once LLVM is installed and clang is in your PATH:

# Restart PowerShell first!
.\scripts\build-windows.ps1

Troubleshooting

"clang not found" after installation

1. Restart your terminal completely (close and reopen PowerShell)
2. Check if LLVM is in PATH:

   $env:PATH -split ';' | Where-Object { $_ -like '*LLVM*' }

3. Manually add to PATH if needed:

   # Typical installation path
   $env:PATH += ";C:\Program Files\LLVM\bin"

Wrong architecture installed

Make sure you installed the ARM64 version of LLVM, not x64. Check:

clang --version
# Should show: Target: aarch64-pc-windows-msvc

Alternative: Use Different Crypto Backend

If you don't want to install LLVM, you can modify the project to use aws-lc-rs instead of ring:

1. In Cargo.toml, find dependencies that use rustls (like reqwest)
2. Add feature flags to use aws-lc-rs:

   [dependencies]
   reqwest = { version = "...", features = ["rustls-tls-aws-lc-rs"], default-features = false }

This is more involved and requires code changes, so installing LLVM is simpler.

Summary

For ARM64 Windows development with Rust:

• Visual Studio Build Tools (MSVC) → Required for linking
• LLVM/Clang → Required for some dependencies with assembly/native code

Both are free and standard tools for native development on Windows.