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Buildroot

Run two commands, get a Linux distro built from source.

  1. Examples
    1. Add a new package in tree
    2. Package with a Kernel module in tree
    3. Out of tree package

Introduction

Takes care of:

  • cross compilation. In other words, compiles GCC for you. Several archs supported.
  • bootloading. Several bootloaders supported.
  • root filesystem generation.
  • tons of packages, e.g. X.org. Packages have a dependency system, but no versioning.

Lots of software supported.

QEMU example

Tested on Ubuntu 16.04.

git clone git://git.buildroot.net/buildroot
cd buildroot
git checkout 2016.05
make qemu_x86_64_defconfig
# Can't use -jN, use `BR2_JLEVEL=2` instead.
make BR2_JLEVEL=2
# Wait.
# cat board/qemu/x86_64/readme.txt
qemu-system-x86_64 -M pc -kernel output/images/bzImage -drive file=output/images/rootfs.ext2,if=virtio,format=raw -append root=/dev/vda -net nic,model=virtio -net user

QEMU x86 nographic

https://www.hiroom2.com/2016/05/20/ubuntu-16-04-build-buildroot-and-run-qemu/

qemu -nographic -append 'console=ttyS0'

At Buildroot 7e85734709e0da78cc399c1b85655528e2d5f209 requires:

sed -i -e 's/BR2_TARGET_GENERIC_GETTY_PORT="tty1"/BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"/g' .config

TODO: but why does it work on: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/b8f190cc24b4f7474894b68a5510a8f3d767843d even without changing it? Buildroot version difference?

ARM

Full QEMU command documented under board/qemu/*/readme.txt.

The obvious x86 analog just works, beauty.

The only thing is that you have to move the x86 output away if you have one:

mv output output.x86~
make qemu_arm_versatile_defconfig
make
qemu-system-arm -M versatilepb -kernel output/images/zImage -dtb output/images/versatile-pb.dtb -drive file=output/images/rootfs.ext2,if=scsi,format=raw -append "root=/dev/sda console=ttyAMA0,115200" -serial stdio -net nic,model=rtl8139 -net user -nographic

Then in QEMU:

cat /proc/cpuinfo

Vexpress requires a more recent QEMU, 2.0.0 does not work, but the 2.7.0 built with QEMU did.

TODO: Ctrl + C kills the emulator itself. Why? Not like that in X86.

Don't ask for password at login

http://unix.stackexchange.com/questions/299408/how-to-login-automatically-without-typing-root-in-buildroot-x86-64-qemu

config

All options are stored in .config before build. The .config file fully specifies the entire system.

Make and environment variables don't in general override options:

# Does not work.
#make defconfig BR2_SOME_OPT=y

Whenever you do make, make oldconfig gets run. make oldconfig removes any new options you've added to the file, unless they are specified under package/Config.in.

Some configs are not put on the .config, while others are commented out. TODO: commented out means dependencies and have been met, removed not?

Important configurations

LINUX_KERNEL_VERSION="4.5.3"
BR2_GCC_VERSION_4_9_X=y

Add a file to the distro

mkdir a
mkdir a/b
date >a/b/c
make BR2_ROOTFS_OVERLAY='a'

Outcome: the root of the generated filesystem now contains /b/c.

Permanent storage filesystem

TODO

Remove package

Currently impossible.

For simple cases, just remove the files from:

rm output/target/usr/bin/hello

random: nonblocking pool is initialized

TODO how to stop printing that

Projects that use Buildroot:

Games

Placed under /usr/bin and /usr/games.

Grouped under packages/Config.in:

menu "Games"

Many / all are SDL based. It seems that SDL has an fbdev mode that dispenses X11.

prdoom

chocolate-doom

Doom clones.

This shows one running on uclinux blackfin SDL DirectFB: https://www.youtube.com/watch?v=fKyQOntPEFs

ltris

lbreakout2

From: http://lgames.sourceforge.net/about.php

Simple SDL based games L stands for Linux.

Should be able to run on framebuffer? But both on TTY and X11 they fail with:

set_video_mode: cannot allocate screen: Couldn't set console screen info

Looks like this is caused by the call: https://www.libsdl.org/release/SDL-1.2.15/docs/html/sdlsetvideomode.html

fbset seems to do the same calls, and fails in the same way.

opentyrian

Takes over screen and hangs.

sl

Classic steam locomotive sl typo corrector. Text only.

gnuchess

CLI chess.

X11

http://unix.stackexchange.com/questions/70931/install-x11-on-my-own-linux-system

GUI

SDL without X11

Web browser

Debugging tools

The basics: always compile with:

  • debugging symbols
  • gdb and gdbserver on target. Requires toolchain with thread support, e.g. glibc.
  • host cross gdb
  • strace
  • QEMU: buildroot can even compile QEMU!

sshd

http://stackoverflow.com/a/39301480/895245

nc

netcat

Not enabled on BusyBox by default, see: package/busybox/default.config

But we have ping (TODO from where?), so whatever.

Boards

Raspberry pi

TODO: how to emulate with QEMU? aarch procedure did no work, no dtb file.

Just worked on a PI2 via UART. No sshd daemon though.

Firefly

UML

User mode Linux

TODO: supported or not?

Direct linux in rootfs failed.

Contributing

CI: http://autobuild.buildroot.net/