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Example project using Rust for Xen unikernels

This is an example build of Rust building a full unikernel for Xen.

Building for x86_64:

# cargo build --target x86_64-xen-pv.json -Zbuild-std=core -Zbuild-std-features=compiler-builtins-mem

And to generate assember files in target/x86_64-xen-pv/{release|debug}/deps/

# RUSTFLAGS="--emit asm -C llvm-args=-x86-asm-syntax=intel" cargo build --target x86_64-xen-pv.json -Zbuild-std=core -Zbuild-std-features=compiler-builtins-mem

Building for aarch64:

# cargo build --target aarch64-xen-hvm.json -Zbuild-std=core -Zbuild-std-features=compiler-builtins-mem

And to generate assember files in target/aarch64-xen-hvm/{release|debug}/deps/

# RUSTFLAGS="--emit asm" cargo build --target aarch64-xen-hvm.json -Zbuild-std=core -Zbuild-std-features=compiler-builtins-mem

On aarch64 Xen accept a binary type unikernel and as such the ELF resulting from the cargo builds needs to be converted as follow:

# aarch64-linux-gnu-objcopy target/aarch64-xen-hvm/release/oxerun -O binary target/aarch64-xen-hvm/release/oxerun.bin

Running the unikernel on QEMU:

$ qemu-system-aarch64 --version
QEMU emulator version 6.0.94 (v6.1.0-rc4-2-gecf5e5ec1f44)
Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developers
$
$ qemu-system-aarch64 \
	-machine virt,virtualization=on \
	-cpu cortex-a57 -serial mon:stdio \
	-device virtio-net-pci,netdev=net0				\
	-netdev user,id=net0,hostfwd=tcp::8022-:22			\
	-device virtio-scsi-pci \
	-drive file=debian-buster-arm64,index=0,id=hd0,if=none,format=raw \
	-device scsi-hd,drive=hd0 \
	-display none \
	-m 8192 -smp 4\
	-kernel $(PATH_TO_XEN)/xen/xen \
	-device guest-loader,addr=0x80000000,kernel=$(PATH_TO_XEN_SYS)/xen-sys/target/aarch64-xen-hvm/release/oxerun.bin

In the above the unikernel is loaded at address 0x80000000, which means that Xen will relocate the binary image to 0x60000000 before jumping to it. The aarch64 LD script for the unikernel, i.e aarch64-xen-hvm.ld, links the image at address 0x60000000. At this time the unikernel is run on a flat memory model without MMU support.