Buildroot on Rishav's Digital Garden

Buildroot on QEMU

Tue, 25 Nov 2025 19:07:00 +0000

Overview

Buildroot is a powerful tool that automates building cross‑compilers, kernel images, bootloaders, root filesystems, and entire minimal Linux environments. Combined with QEMU, it provides a fast and fully emulated setup without needing physical hardware.

Steps

0. Dependencies

Before building Buildroot, ensure the following packages are installed on your host system:

For Debian/Ubuntu:

sudo apt install build-essential git wget cpio unzip rsync bc python3 \
 qemu-system-arm qemu-system-misc qemu-utils flex bison libssl-dev

For Fedora:

Generating Package Patch for Buildroot

Tue, 20 May 2025 10:13:00 +0000

Generating a Patch Using `diff`

1. Extract the Original Source

Ensure you have a pristine copy of the original source for comparison. You can extract it from the tarball in the dl directory:

tar -xf dl/<package>-<version>.tar.gz -C /tmp/

This will create a directory like /tmp/<package>-<version>/.

Using buildroot’s mechanism

Clean the build directory and apply current patches of buildroot

make <pkg>-dirclean # Remove <pkg> build directory
make <pkg>-extract # Extract <pkg> sources
make <pkg>-patch # Apply patches to <pkg> (Optional)

cp -r output/build/<package> /tmp/

2. Generate the Patch

Use the diff command to create a unified diff between the original and modified sources:

External Toolchain in Buildroot

Fri, 04 Apr 2025 12:00:00 +0000

Using External Toolchain

Option 1: Give tarball URL

Specify URL for the tarball in BR_TOOLCHAIN_EXTERNAL_URL

Example:

BR_TOOLCHAIN_EXTERNAL_URL=http://artifactory/my-toolchain.tar.xz

In this case you will have to deselect BR2_PRIMARY_SITE_ONLY option

Option 2: Give tarball relative dl path

If BR2_PRIMARY_SITE_ONLY option is selected then you have to keep the toolchain inside dl/toolchain-external-custom/ directory and pass the name of tarball to BR_TOOLCHAIN_EXTERNAL_URL

Example:

BR2_PRIMARY_SITE="http://artifactory/buildroot-sources"
BR2_PRIMARY_SITE_ONLY=y
BR_TOOLCHAIN_EXTERNAL_URL=my-toolcahin.tar.xz

This will extract the toolchain to buildroot’s build directory output/host/opt/ext-toolchain

Buildroot Relocatable SDK

Mon, 10 Mar 2025 12:17:00 +0000

Overview

A relocatable toolchain/SDK is a self-contained set of cross-compilation tools that can be moved to different locations without breaking dependencies. Buildroot provides an option to generate such a toolchain, allowing developers to use it for cross-compiling applications without depending on a fixed absolute path.

Prepare Relocatable SDK

Configure Buildroot for SDK Generation

Disable BusyBox and set /bin/sh to None under System configuration. This prevents unnecessary shell dependencies within the SDK, ensuring better relocatability.

Making File System

Mon, 11 Nov 2024 19:14:00 +0000

Overview

Get the final files into a directory eg. target and treat it as root(/) directory of target board/system.
Generate users eg. root, admin, ssh, etc
Generate device lists
Clean few files
Generate ext image using mkfs

Taking reference from buildroot common.mk and ext2.mk

scripts/makedevs -d output/build/buildroot-fs/full_devices_table.txt output/build/buildroot-fs/ext2/target

mkfs.ext4 -d output/build/buildroot-fs/ext2/target -r 1 -N 0 -m 5 -L rootfs -O ^64bit output/images/rootfs.ext2 2G

# Fakeroot execution complete

/opt/rk3588_nvrx/host/sbin/resize2fs -M output/images/rootfs.ext2
/opt/rk3588_nvrx/host/sbin/e2fsck -fy /output/images/rootfs.ext2
/opt/rk3588_nvrx/host/sbin/resize2fs -M /output/images/rootfs.ext2

Fakeroot Script

#!/bin/sh
set -ex
chown -h -R 0:0 $(TARGET)
$(HOST_DIR)/bin/makedevs -d full_devices_table.txt $(TARGET)
$(HOST_DIR)/sbin/mkfs.ext4 -d $(TARGET) -r 1 -N 0 -m 5 -L "rootfs" -O ^64bit rootfs.ext2 "2G"

Post EXT4

$(HOST_DIR)/sbin/resize2fs -M rootfs.ext2
$(HOST_DIR)/sbin/e2fsck -fy rootfs.ext2
$(HOST_DIR)/sbin/tune2fs -m 5 rootfs.ext2
$(HOST_DIR)/sbin/resize2fs -M rootfs.ext2

Testing on Host

sudo mount -o loop path/to/rootfs.ext4 /tmp/fs_path

Makedevs

Creates a batch of special files as specified in a device table.

Buildroot on Rishav's Digital Garden

Buildroot on QEMU

Overview

Steps

0. Dependencies

Generating Package Patch for Buildroot

Generating a Patch Using diff

1. Extract the Original Source

Using buildroot’s mechanism

2. Generate the Patch

External Toolchain in Buildroot

Using External Toolchain

Option 1: Give tarball URL

Option 2: Give tarball relative dl path

Buildroot Relocatable SDK

Overview

Prepare Relocatable SDK

Configure Buildroot for SDK Generation

Making File System

Overview

Fakeroot Script

Post EXT4

Testing on Host

Makedevs

Generating a Patch Using `diff`