README

On OS X we don't have some headers from a Linux world which seems to be essential for building a Linux kernel. This small project aims to provide the missing headers and a short readme for those who (like me) wants to work with Linux on Mac as native as possible.

Building a Linux kernel

1. Install libelf with

brew install libelf

2. Clone the repository and copy its files into /usr/local/include:

git clone git@github.com:vgribov/mac-linux-headers.git
cp -r mac-linux-headers/* /usr/local/include

3. Install some GNU stuff to make feel kernel's Makefiles at home:

brew install --with-default-names coreutils gnu-sed grep

To make Linux ELF binaries you'll need a cross compiler. I found a nice one at https://github.com/richfelker/musl-cross-make.

Now you should be able to build the kernel with

make x86_64_defconfig
make CROSS_COMPILE='x86_64-linux-musl-'

To be able to use a menuconfig you should also install gettext and ncurses and link them:

brew install gettext ncurses
brew link --force gettext
brew link --force ncurses

Build and run a minimal Linux in Qemu

This part is based on https://gitlab.eurecom.fr/snippets/23, so all credits go to mailto:renaud.pacalet@telecom-paristech.fr.

1. Download and unpack your preferred Linux kernel version:

wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.1.51.tar.xz
tar xvf linux-4.1.51.tar.xz

2. Prepare a basic Linux kernel configuration:

cd linux-4.1.51
mkdir build
make O=./build allnoconfig
cd ./build
make menuconfig

3. Configure the kernel according to the following:

64-bit kernel ---> yes
General setup ---> Initial RAM filesystem and RAM disk (initramfs/initrd) support ---> yes
General setup ---> Configure standard kernel features ---> Enable support for printk ---> yes
Executable file formats / Emulations ---> Kernel support for ELF binaries ---> yes
Executable file formats / Emulations ---> Kernel support for scripts starting with #! ---> yes
Device Drivers ---> Generic Driver Options ---> Maintain a devtmpfs filesystem to mount at /dev ---> yes
Device Drivers ---> Generic Driver Options ---> Automount devtmpfs at /dev, after the kernel mounted the rootfs ---> yes
Device Drivers ---> Character devices ---> Enable TTY ---> yes
Device Drivers ---> Character devices ---> Serial drivers ---> 8250/16550 and compatible serial support ---> yes
Device Drivers ---> Character devices ---> Serial drivers ---> Console on 8250/16550 and compatible serial port ---> yes
File systems ---> Pseudo filesystems ---> /proc file system support ---> yes
File systems ---> Pseudo filesystems ---> sysfs file system support ---> yes

4. Build the kernel:

make -j8
cd ..

5. Download and unpack your preferred Busybox version:

wget http://busybox.net/downloads/busybox-1.28.3.tar.bz2
tar xvf busybox-1.28.3.tar.bz2

6. Prepare a basic Busybox configuration:

cd busybox-1.28.3
mkdir build
make O=./build defconfig
cd ./build
make menuconfig

7. Configure Busybox according the following:

Busybox Settings ---> Build Options ---> Build BusyBox as a static binary (no shared libs) ---> yes

8. Build and install Busybox:

make -j8
make install
cd ../..

9. Create an initramfs:

mkdir initramfs
cd initramfs
mkdir -p bin sbin etc proc sys usr/bin usr/sbin
cp -a ../busybox-1.28.3/_install/* .

10. Add an init script to the initramfs with the following content:

#!/bin/sh

mount -t proc none /proc
mount -t sysfs none /sys

printf "\nBoot took %s seconds\n\n" $(awk '{ print $1 }' < /proc/uptime)

exec /bin/sh

11. Create the initramfs archive:

chmod +x init
find . | cpio -ov --format=newc | gzip > ../initramfs.cpio.gz
cd ..

12. Install Qemu

brew install qemu

Now you should be able to run and test your minimal Linux with:

qemu-system-x86_64 -kernel $PWD/linux-4.1.51/build/arch/x86_64/boot/bzImage \
                   -initrd $PWD/initramfs.cpio.gz \
                   -nographic -serial mon:stdio \
                   -append 'console=ttyS0 earlyprintk=ttyS0'

Press Ctrl-a x to quit.