Buildroot-Linux-with-gcc_cross_compilation

This repository documents my process of building a minimal Linux image for Raspberry Pi 3 using Buildroot.
The goal is to understand Linux system components like BusyBox, rootfs, and bootloaders through hands-on experimentation.

The system includes:

• A minimal Linux kernel
• BusyBox utilities
• SSH for remote access
• Basic networking setup

Project Details

Item	Description
Target Board	Raspberry Pi 3
Build System	Buildroot
Filesystem Type	ext4
Default Config Used	raspberrypi3_defconfig
Access Method	SSH

Boot Flow

Power On ⇨ Bootloader (loads kernel +dtb) ⇨ Kernel (initiates hardware) ⇨ Mounts (rootfs) ⇨ Runs (BusyBox) ⇨ You get a shell

Installation Steps

Install Prerequisites

$ sudo apt update
$ sudo apt install which sed make binutils build-essential \ diffutils gcc g++ bash patch gzip bzip2 perl tar cpio \ unzip rsync file bc findutils wget python3 libncurses5-dev \ libncursesw5-dev git

Download Buildroot

$ git clone https://github.com/buildroot/buildroot.git

Select the Board

$ make raspberrypi3_defconfig

Customize the Build

$ make menuconfig
$ make linux-menuconfig
$ make busybox-menuconfig

Enable the Root Password

Build the system

$ make

Flash the image to SD Card using

$ sudo dd if=output/images/sdcard.img of=/dev/sdX bc=4M

Booted on Raspberry Pi 3 and accessed via SSH

$ ssh root@10.247.xx.xx

Output Terminal

$ root@10.247.xx.xx's password:

# uname -a
Linux buildroot 6.12.41-v7 #1 SMP Fri Oct 10 20:03:22 IST 2025 armv7l GNU/Linux

# hostname
buildroot

# busybox
BusyBox v1.37.0 (2025-10-10 19:54:00 IST) multi-call binary.
BusyBox is copyrighted by many authors between 1998-2015.
Licensed under GPLv2. See source distribution for detailed
copyright notices.

Usage: busybox [function [arguments]...]
   or: busybox --list[-full]
   or: busybox --show SCRIPT
   or: busybox --install [-s] [DIR]
   or: function [arguments]...

	BusyBox is a multi-call binary that combines many common Unix
	utilities into a single executable.  Most people will create a
	link to busybox for each function they wish to use and BusyBox
	will act like whatever it was invoked as.

Currently defined functions:
	[, [[, addgroup, adduser, ar, arch, arp, arping, ascii, ash, awk, base32, base64, basename, bc, blkid, bunzip2, bzcat, cat, chattr,
	chgrp, chmod, chown, chroot, chrt, chvt, cksum, clear, cmp, cp, cpio, crc32, crond, crontab, cut, date, dc, dd, deallocvt, delgroup,
	deluser, devmem, df, diff, dirname, dmesg, dnsd, dnsdomainname, dos2unix, du, dumpkmap, echo, egrep, eject, env, ether-wake, expr,
	factor, fallocate, false, fbset, fdflush, fdformat, fdisk, fgrep, find, flock, fold, free, freeramdisk, fsck, fsfreeze, fstrim, fuser,
	getfattr, getopt, getty, grep, gunzip, gzip, halt, hdparm, head, hexdump, hexedit, hostid, hostname, hwclock, i2cdetect, i2cdump,
	i2cget, i2cset, i2ctransfer, id, ifconfig, ifdown, ifup, inetd, init, insmod, install, ip, ipaddr, ipcrm, ipcs, iplink, ipneigh,
	iproute, iprule, iptunnel, kill, killall, killall5, klogd, last, less, link, linux32, linux64, linuxrc, ln, loadfont, loadkmap, logger,
	login, logname, losetup, ls, lsattr, lsmod, lsof, lspci, lsscsi, lsusb, lzcat, lzma, lzopcat, makedevs, md5sum, mdev, mesg, microcom,
	mim, mkdir, mkdosfs, mke2fs, mkfifo, mknod, mkpasswd, mkswap, mktemp, modprobe, more, mount, mountpoint, mt, mv, nameif, netstat, nice,
	nl, nohup, nologin, nproc, nslookup, nuke, od, openvt, partprobe, passwd, paste, patch, pidof, ping, pipe_progress, pivot_root,
	poweroff, printenv, printf, ps, pwd, rdate, readlink, readprofile, realpath, reboot, renice, reset, resize, resume, rm, rmdir, rmmod,
	route, run-init, run-parts, runlevel, sed, seedrng, seq, setarch, setconsole, setfattr, setkeycodes, setlogcons, setpriv, setserial,
	setsid, sh, sha1sum, sha256sum, sha3sum, sha512sum, shred, sleep, sort, start-stop-daemon, strings, stty, su, sulogin, svc, svok,
	swapoff, swapon, switch_root, sync, sysctl, syslogd, tail, tar, tee, telnet, test, tftp, time, top, touch, tr, traceroute, tree, true,
	truncate, ts, tsort, tty, ubirename, udhcpc, uevent, umount, uname, uniq, unix2dos, unlink, unlzma, unlzop, unxz, unzip, uptime,
	usleep, uudecode, uuencode, vconfig, vi, vlock, w, watch, watchdog, wc, wget, which, who, whoami, xargs, xxd, xz, xzcat, yes, zcat

# ls /proc
1              158            17715          230            45             72             bus            irq            schedstat
108            15841          17731          232            47             74             cgroups        kallsyms       self
112            159            17734          24             48             75             cmdline        key-users      slabinfo
116            15974          17741          26             49             76             consoles       keys           softirqs
11636          16             17742          27             5              77             cpu            kmsg           stat
11655          161            17753          28             50             78             cpuinfo        kpagecgroup    swaps
12             16172          17754          29             51             79             crypto         kpagecount     sys
13             162            18             3              52             8              device-tree    kpageflags     sysrq-trigger
132            163            183            31             55             80             devices        latency_stats  sysvipc
14             164            19             32             56             81             diskstats      loadavg        thread-self
14049          17             2              33             57             82             driver         locks          timer_list
14889          171            20             34             6              83             execdomains    meminfo        tty
14954          17345          206            36             60             85             fb             misc           uptime
15             17388          21             4              61             86             filesystems    modules        version
152            17471          212            41             68             87             fs             mounts         vmallocinfo
15376          17596          22             42             69             88             interrupts     net            vmstat
157            17712          222            43             7              89             iomem          pagetypeinfo   zoneinfo
15723          17714          23             44             71             buddyinfo      ioports        partitions

# cat /proc/cpuinfo
processor	: 0
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 38.40
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 1
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 38.40
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 2
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 38.40
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

processor	: 3
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 38.40
Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xd03
CPU revision	: 4

Hardware	: BCM2835
Revision	: a22082
Serial		: 000000007c78add3
Model		: Raspberry Pi 3 Model B Rev 1.2

# ls /
bin           dev           lib           linuxrc       media         opt           root          sbin          tmp           var
crond.reboot  etc           lib32         lost+found    mnt           proc          run           sys           usr

# mount
/dev/root on / type ext4 (rw,relatime)
devtmpfs on /dev type devtmpfs (rw,relatime,size=426292k,nr_inodes=106573,mode=755)
proc on /proc type proc (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620,ptmxmode=666)
tmpfs on /dev/shm type tmpfs (rw,relatime)
tmpfs on /tmp type tmpfs (rw,relatime)
tmpfs on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755)
sysfs on /sys type sysfs (rw,relatime)

# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root               107.0M     78.3M     20.3M  79% /
devtmpfs                416.3M         0    416.3M   0% /dev
tmpfs                   448.8M         0    448.8M   0% /dev/shm
tmpfs                   448.8M    292.0K    448.5M   0% /tmp
tmpfs                   448.8M     40.0K    448.8M   0% /run

# ls /etc
cron           fstab          hosts          issue          nsswitch.conf  profile        resolv.conf    shells
dhcpcd.conf    group          init.d         mtab           os-release     profile.d      services       ssh
dropbear       hostname       inittab        network        passwd         protocols      shadow         ssl

Cross Compilation for GCC support

Toolchain Setup

We use an external ARM toolchain located on the Desktop for cross-compilation.

(https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads)

Check the host machine Configuration:

Download the toolchain refering to your host system configuration

~/Desktop$ gcc -dumpmachine
x86_64-linux-gnu

Extract the Toolchain

$ tar -xvf gcc-arm-10.3-2021.07-x86_64-arm-none-linux-gnueabihf.tar.xz 

Verify the Binary Path

Navigate to the bin directory to confirm the path

$ cd gcc-arm-10.3-2021.07-x86_64-arm-none-linux-gnueabihf/
$ pwd

Configure the Environment Variable

The toolchain of your path will be temporarily added for current session

$ export PATH=/home/user/Downloads/gcc-arm-10.3-2021.07-x86_64-arm-none-linux-gnueabihf/bin:$PATH

Make it Permanent

$ echo 'export PATH=/home/user/Downloads/gcc-arm-10.3-2021.07-x86_64-arm-none-linux-gnueabihf/bin:$PATH' >> ~/.bashrc
$ source ~/.bashrc

Verify the installation

Confirm the compiler version & compiler is accessible

~/Desktop$ arm-none-linux-gnueabihf-g++ --version
arm-none-linux-gnueabihf-g++ (GNU Toolchain for the A-profile Architecture 10.3-2021.07 (arm-10.29)) 10.3.1 20210621
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE

Create the test file

Example to Print hello on the Build machine

~/Desktop$ nano test.cpp

#include <iostream>

int main()
{
        std::cout<< "Hello.."<<std::endl;
        return 0;
        
}

Compile the sketch

Use the -static flag to ensure the binary runs on the target without library conflicts.

~/Desktop$ arm-none-linux-gnueabihf-g++ -o test test.cpp -static

Deployment via SCP

Deploy the compiled binary to the running Buildroot system:

~/Desktop$ scp ./test root@10.xxx.74.xx:/tmp

Log in the board

Once you are logged into the board's terminal, navigate to the /tmp folder, make the file executable, and run it:

ssh root@10.xxx.xx.xx
# cd /tmp
# chmod +x test
# ./test

Output

Hello..