Running U-Boot & Linux Kernel in QEMU

Installing Pre-requisites

Following command can be executed to install all software necessary for this tutorial:

sudo apt update && sudo apt install build-essential libncurses-dev rsync git ninja-build libglib2.0-dev libpixman-1-dev bison flex libssl-dev wget unzip bc file

Prepare a working directory:

mkdir tech.io && cd tech.io

This will be considered as the root working directory for this tutorial.

Spaces/Tabs/Newline in $PATH

If you're trying WSL (Windows Subsystem for Linux) on Windows, the system's $PATH variable may contain whitespaces. If that's the case, commands which depend on $PATH won't work. You can inspect $PATH by the following command:

echo $PATH

If $PATH contains whitespaces, you have two options:

1. Remove the entries which contain whitespaces. If they start with /mnt, removing them will remove dependencies on Windows system.
2. Surround the entries with double quotes ("). Like /mnt/c/Program Files/Java/jdk-16.0.1/bin should be "/mnt/c/Program Files/Java/jdk-16.0.1/bin".

Once you've done constructing new $PATH, make them available in the terminal session using the following command:

export PATH=<new path entries>

For instance:

export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/usr/lib/wsl/lib

Installing Toolchain

Buildroot is a software package that can generate necessary tools for cross compiling code base for embedded Linux. This tutorial will use version v2023.08.

# Download the file
wget https://buildroot.org/downloads/buildroot-2023.08.tar.gz

# Extract from compressed file
tar -xf buildroot-2023.08.tar.gz

tar parameters:

• x = Extract files
• f = Use archive file

cd buildroot-2023.08

# To generate toolchain configuration file
make menuconfig

Select the following options:

1. Target options
   1. Target Architecture > RISCV
   2. Target Architecture Size > 64-bit
2. Toolchain
   1. C library > musl
   2. Kernel Headers > Linux 6.4.x kernel headers
   3. Binutils Version > binutils 2.41
   4. GCC compiler Version > gcc 13.x

Exit and save the configuration. Build the toolchain:

make sdk -j$(nproc)

• -j$(nproc) = $(nproc) will expand to number of available processing units, -j flag will paralellize build utilizing the output indicated by $(nproc)

The output is the file output/images/riscv64-buildroot-linux-musl_sdk-buildroot.tar.gz. Extract it:

# Create a toolchain directory for toolchain extraction
cd ..
mkdir toolchain && cd toolchain

tar -xf ../buildroot-2023.08/output/images/riscv64-buildroot-linux-musl_sdk-buildroot.tar.gz

All the important binaries are now in riscv64-buildroot-linux-musl_sdk-buildroot/bin directory. The RISC-V compier is riscv64-linux-gcc. Fix the hardcoded paths by running the script:

riscv64-buildroot-linux-musl_sdk-buildroot/relocate-sdk.sh

Place the binaries in system path:

# Go to the working directory
cd ..

# Create a script named tech.io-env.sh to update system path
printf "export PATH=~/tech.io/toolchain/riscv64-buildroot-linux-musl_sdk-buildroot/bin:$PATH\n" > tech.io-env.sh

• The printf command is used to print something on the terminal.
• The > operator redirects the terminal output to a file.

Update environment variable by running the script using source & test:

source tech.io-env.sh
riscv64-linux-gcc --version

It presented the version as follows:

riscv64-linux-gcc.br_real (Buildroot 2023.08) 13.2.0
Copyright (C) 2023 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.

This confirms that the necessary toolchain has been installed and added to the system path.