Building the Xen compiler

Xen’s compiler is an OCaml executable. Its host architecture is independent of the architecture of programs generated by Xen.

To use a released compiler, follow installation for .deb and tar.gz packages. This guide covers building the compiler from source.

Build environment	OCaml needed
Linux x86_64, building an x86_64 compiler	Native x86_64 OCaml
Linux AArch64, building an AArch64 compiler	Native AArch64 OCaml
Linux x86_64, building an AArch64 compiler	Native x86_64 OCaml and an AArch64 cross OCaml toolchain

Cross OCaml runs on the build host and emits code for another CPU. Installing an AArch64-native OCaml executable on x86_64 does not provide that cross toolchain. See AArch64 cross compilation.

Prerequisites

• Native OCaml with ocamlc and ocamlopt on PATH; OCaml 5.5.0 is the reference toolchain.
• Dune 3.18 or later; Dune 3.24.2 is the reference build version.
• GNU Make for the repository’s build commands.
• Python 3.10 or later for packaging and test scripts; dpkg-dev for .deb creation.

The cross toolchain must match the native OCaml version exactly. Compiler tests also require Python 3.10 or later and binutils; see the test guide. Generated Xen programs use a static runtime and do not require a C compiler, assembler, linker or libc. Building OCaml itself requires a native C toolchain.

Installing native OCaml

With an initialized opam installation, create a native switch and install Dune:

opam switch create xen-native 5.5.0
eval "$(opam env --switch=xen-native)"
opam install 'dune>=3.18'

Alternatively, build native OCaml from the official sources. On Ubuntu/Debian, the following packages provide the native build tools:

sudo apt install build-essential pkg-config libzstd-dev curl

Use a fresh source directory and a persistent, user-owned installation prefix:

XEN_OCAML_SOURCE_ROOT="$HOME/.local/src/xen-ocaml-5.5.0"
XEN_OCAML_NATIVE_PREFIX="$HOME/.local/opt/ocaml-native-5.5.0"
mkdir -p "$XEN_OCAML_SOURCE_ROOT/native"
curl --fail --location https://github.com/ocaml/ocaml/archive/refs/tags/5.5.0.tar.gz \
  --output "$XEN_OCAML_SOURCE_ROOT/ocaml-5.5.0.tar.gz"
tar -xzf "$XEN_OCAML_SOURCE_ROOT/ocaml-5.5.0.tar.gz" \
  -C "$XEN_OCAML_SOURCE_ROOT/native" --strip-components=1
cd "$XEN_OCAML_SOURCE_ROOT/native"
./configure --prefix="$XEN_OCAML_NATIVE_PREFIX"
make -j2
make install
export PATH="$XEN_OCAML_NATIVE_PREFIX/bin:$PATH"

Install Dune separately using its official installation instructions. Check the tools selected by PATH before building Xen:

ocamlc -version
ocamlopt -version
dune --version

The native OCaml source procedure follows OCaml’s installation guide. Use matching sources when selecting a different OCaml version.

Building Xen

Run from the Xen repository root:

make build
compiler/dist/xen version
compiler/dist/xen check examples/demo.xen
compiler/dist/xen run examples/demo.xen

make build runs dune build @release. Dune builds _build/default/compiler/main.exe and promotes the release executable to compiler/dist/xen. Native Linux AArch64 uses the same commands without a cross workspace. The CLI default target follows the compiler’s OCaml build architecture; both Linux targets use scoped AOT optimization.

Compiler version

VERSION declares the default compiler version. Make embeds a supplied override:

make build VERSION=0.1.0-demo.2
compiler/dist/xen version

Direct Dune builds use VERSION or XEN_BUILD_VERSION. Binary and source package version handling is described in packaging.

Testing and packaging

Use the test guide for make test and focused host suites. Native AArch64 host validation uses python3 scripts/test.py --suite host and --suite arm64; the full suite also includes x86_64 execution/scoped AOT checks. Select the current host CPU when packaging a native build:

make package-deb PACKAGE_ARCHS=x86_64
make release-package PACKAGE_ARCHS=x86_64

Use PACKAGE_ARCHS=aarch64 on a native AArch64 host. The first command creates only .deb; the second creates .deb and tar.gz. Without a CPU selection, make package, make package-deb and make release-package request both CPUs and need the other CPU’s cross toolchain. Debian cross packaging also needs target library metadata. See packaging for the directory layout, version mapping, glibc baseline and GitHub release procedure.