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Add cross-compilation support to Makefile #461

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c71a088
Makefile: cross-compile init.c on macOS with clang, lld and an auto-g…
nohajc Nov 10, 2025
f658fd5
README.md: document build and installation steps of macOS generic var…
nohajc Nov 29, 2025
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1 change: 1 addition & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
Expand Up @@ -17,3 +17,4 @@ examples/nitro
examples/consoles
examples/rootfs_fedora
test-prefix
/linux-sysroot
59 changes: 56 additions & 3 deletions Makefile
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Expand Up @@ -82,6 +82,9 @@ ifeq ($(TIMESYNC),1)
endif

OS = $(shell uname -s)
ARCH = $(shell uname -m)
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@nohajc nohajc Nov 11, 2025 •
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This can return arm64 on macOS or aarch64 on Linux but clang seems happy with either in the target triple.

DEBIAN_DIST ?= bookworm
ROOTFS_DIR = linux-sysroot

KRUN_BINARY_Linux = libkrun$(VARIANT).so.$(FULL_VERSION)
KRUN_SONAME_Linux = libkrun$(VARIANT).so.$(ABI_VERSION)
Expand All @@ -103,22 +106,70 @@ ifeq ($(PREFIX),)
PREFIX := /usr/local
endif

.PHONY: install clean test test-prefix $(LIBRARY_RELEASE_$(OS)) $(LIBRARY_DEBUG_$(OS)) libkrun.pc
.PHONY: install clean test test-prefix $(LIBRARY_RELEASE_$(OS)) $(LIBRARY_DEBUG_$(OS)) libkrun.pc clean-sysroot clean-all

all: $(LIBRARY_RELEASE_$(OS)) libkrun.pc

debug: $(LIBRARY_DEBUG_$(OS)) libkrun.pc

ifeq ($(OS),Darwin)
# If SYSROOT_LINUX is not set and we're on macOS, generate sysroot automatically
ifeq ($(SYSROOT_LINUX),)
SYSROOT_LINUX = $(ROOTFS_DIR)
SYSROOT_TARGET = $(ROOTFS_DIR)/.sysroot_ready
else
SYSROOT_TARGET =
endif
# Cross-compile on macOS with the LLVM linker (brew install lld)
CC_LINUX=/usr/bin/clang -target $(ARCH)-linux-gnu -fuse-ld=lld -Wl,-strip-debug --sysroot $(SYSROOT_LINUX) -Wno-c23-extensions
else
# Build on Linux host
CC_LINUX=$(CC)
SYSROOT_TARGET =
endif

ifeq ($(BUILD_INIT),1)
INIT_BINARY = init/init
$(INIT_BINARY): $(INIT_SRC)
$(CC) -O2 -static -Wall $(INIT_DEFS) -o $@ $(INIT_SRC) $(INIT_DEFS)
$(INIT_BINARY): $(INIT_SRC) $(SYSROOT_TARGET)
$(CC_LINUX) -O2 -static -Wall $(INIT_DEFS) -o $@ $(INIT_SRC) $(INIT_DEFS)
endif

NITRO_INIT_BINARY= init/nitro/init
$(NITRO_INIT_BINARY): $(NITRO_INIT_SRC)
$(CC) -O2 -static -Wall $(NITRO_INIT_LD_FLAGS) -o $@ $(NITRO_INIT_SRC) $(NITRO_INIT_LD_FLAGS)

# Sysroot preparation rules for cross-compilation on macOS
DEBIAN_PACKAGES = libc6 libc6-dev libgcc-12-dev linux-libc-dev
ROOTFS_TMP = $(ROOTFS_DIR)/.tmp
PACKAGES_FILE = $(ROOTFS_TMP)/Packages.xz

.INTERMEDIATE: $(PACKAGES_FILE)

$(ROOTFS_DIR)/.sysroot_ready: $(PACKAGES_FILE)
@echo "Extracting Debian packages to $(ROOTFS_DIR)..."
@for pkg in $(DEBIAN_PACKAGES); do \
DEB_PATH=$$(xzcat $(PACKAGES_FILE) | sed '1,/Package: '$$pkg'$$/d' | grep Filename: | sed 's/^Filename: //' | head -n1); \
DEB_URL="https://deb.debian.org/debian/$$DEB_PATH"; \
DEB_NAME=$$(basename "$$DEB_PATH"); \
if [ ! -f "$(ROOTFS_TMP)/$$DEB_NAME" ]; then \
echo "Downloading $$DEB_URL"; \
curl -fL -o "$(ROOTFS_TMP)/$$DEB_NAME" "$$DEB_URL"; \
fi; \
cd $(ROOTFS_TMP) && ar x "$$DEB_NAME" && cd ../..; \
tar xf $(ROOTFS_TMP)/data.tar.* -C $(ROOTFS_DIR); \
rm -f $(ROOTFS_TMP)/*.deb $(ROOTFS_TMP)/data.tar.* $(ROOTFS_TMP)/control.tar.* $(ROOTFS_TMP)/debian-binary; \
done
@touch $@

$(PACKAGES_FILE):
@echo "Downloading Debian package index for $(DEBIAN_DIST)/$(ARCH)..."
@mkdir -p $(ROOTFS_TMP)
@curl -fL -o $@ https://deb.debian.org/debian/dists/$(DEBIAN_DIST)/main/binary-$(ARCH)/Packages.xz

clean-sysroot:
rm -rf $(ROOTFS_DIR)


$(LIBRARY_RELEASE_$(OS)): $(INIT_BINARY)
cargo build --release $(FEATURE_FLAGS)
ifeq ($(SEV),1)
Expand Down Expand Up @@ -175,6 +226,8 @@ clean:
rm -rf test-prefix
cd tests; cargo clean

clean-all: clean clean-sysroot

test-prefix/lib64/libkrun.pc: $(LIBRARY_RELEASE_$(OS))
mkdir -p test-prefix
PREFIX="$$(realpath test-prefix)" make install
Expand Down
23 changes: 23 additions & 0 deletions README.md
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Expand Up @@ -202,6 +202,29 @@ sudo make EFI=1 install

```

### macOS (generic variant)

#### Requirements

* A working [Rust](https://www.rust-lang.org/) toolchain
* A host running macOS 14 or newer
* Homebrew packages `lld` and `xz`

#### Compiling

```
make [FEATURE_OPTIONS]
```

The [init](init/init.c) binary is cross-compiled using clang and lld.
A suitable sysroot is automatically generated by the Makefile from Debian repository.

#### Installing

```
sudo make [FEATURE_OPTIONS] install
```

## Using the library

Despite being written in Rust, this library provides a simple C API defined in [include/libkrun.h](include/libkrun.h)
Expand Down