Workshop

Using QEMU to Get Started with Embedded Linux

Mohammed Billoo

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01:55:00

EOC 2022

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Mohammed Billoo

Mohammed Billoo is Founder of MAB Labs, LLC. He has over 12 years of experience architecting, designing, implementing, and testing embedded software, with a core focus on embedded Linux. This includes custom board bring-up, writing custom device drivers, and writing application code. Mohammed also contributes to the Linux kernel and is an active participant in numerous open-source efforts. He is also an Adjunct Professor of Electrical Engineering at The Cooper Union for the Advancement of Science and Art, where he teaches courses in Digital Logic Design, Computer Architecture, and Advanced Computer Architecture. Mohammed received both his Bachelor's and Master's of Electrical Enginering from the same institution.

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Topics Covered

Tools Embedded Linux Open Source

Workshop

Using QEMU to Get Started with Embedded Linux

Mohammed Billoo

01:55:00 EOC 2022

Mohammed Billoo

01:55:00

Getting started with embedded Linux can be a daunting task due to the inherent complexity of the Linux kernel; it can also be costly, since generally any sort of driver development and testing requires hardware. QEMU can serve as an alternative to allow engineers to get started with embedded Linux with minimal cost.

In this workshop, Mohammed Billoo will walk through what QEMU is and the different workflows that it enables, with hands-on demonstrations that attendees can follow along. Demonstrations will include setting up QEMU to emulate an ARM-based machine on a x86-based host PC and launching into a terminal, using QEMU to step through the Linux kernel, and developing and testing a simple device driver with device emulation in QEMU.

This workshop has the following prerequisites:

Install Ubuntu >= 18.04 on your PC (either on bare-metal or as a VM):
Install qemu-system-arm (sudo apt-get install qemu-system-arm)
Install your favorite text editor (e.g. nano, vim)
Clone the buildroot repository on your Ubuntu installation by executing the following from the command line: $> git clone git://git.buildroot.net/buildroot
Clone the qemu repository on your Ubuntu installation by executing the following from the command line: $> git clone --depth 1 --branch v6.2.0 https://github.com/qemu/qemu.git
Clone the Linux kernel repository on your Ubuntu installation by executing the following from the command line: $> git clone --depth 1 --branch v5.17 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

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What is the primary practical reason Mohammed Billoo recommends using QEMU when getting started with embedded Linux?

A QEMU replaces the need for a cross-compiler by automatically recompiling code for the host CPU.

B QEMU lets you emulate the processor, board devices, and run a complete target system as a user-space process so you can develop and test kernel and drivers without physical hardware.

C QEMU guarantees identical real-time timing and performance to the final hardware, so no hardware testing is needed.

D QEMU automatically converts user-space ARM applications to native x86 binaries at build time.

E QEMU is primarily useful because it removes the need for a device tree when running an embedded system.

According to the workshop, which four components are the critical building blocks you must combine (with a cross-compiler) to produce an Embedded Linux image?

A Bootloader, kernel, device tree, root filesystem

B Kernel, cross-compiler, sysfs, initramfs

C Bootloader, Makefile, glibc, device tree

D Root filesystem, u-boot, compiler, kernel modules only

E Device tree, package manager, kernel headers, bootloader

What workflow does Mohammed demonstrate for source-level debugging the Linux kernel under QEMU?

A Boot QEMU normally, SSH into the guest, and use strace to step through kernel functions.

B Run QEMU with -s -S to start a GDB server and freeze the CPU, then connect with a cross-architecture GDB to the kernel vmlinux and set breakpoints/step through start_kernel.

C Use QEMU's serial console only and place print statements in the kernel to trace execution.

D Attach gdbserver inside the guest userland and use it to debug kernel C code directly.

E Compile the kernel without debug symbols and use objdump to inspect live stack frames over the serial port.

Which combination of actions did the speaker use to test an I2C device driver in QEMU without real hardware?

A Build the kernel without modifying the device tree, load the kernel module manually, and rely on i2c-tools to magically probe devices that don't exist.

B Write a user-space mock to simulate the sensor, keep QEMU untouched, and expect the kernel's probe to run automatically.

C Add an I2C device entry into the kernel's device tree so the kernel will probe it, and build QEMU with the corresponding emulated device (QOM) and attach it at the matching I2C address; optionally use QMP to change sensor values at runtime.

D Use only Buildroot settings to enable the driver and assume QEMU will create the hardware automatically without any QEMU-side changes.

E Change the kernel to ignore device trees and manually register the device from userland so QEMU doesn't need any changes.

How does Mohammed describe the role of the cross‑compiler/toolchain and the ABI in embedded Linux development?

A The cross-compiler is optional; you can build target binaries with the host compiler by setting architecture flags.

B The toolchain provides the ABI bridge between user-space applications and the kernel; the toolchain prefix (e.g., arm-linux-gnueabi) indicates the toolchain targets the Linux ABI for that architecture.

C The ABI is irrelevant for embedded Linux because user-space always uses syscalls directly without dependency on the toolchain.

D The cross-compiler only matters for bootloaders; user-space and kernel code can be compiled with any compiler.

E You must always use a 'none' ABI for embedded Linux toolchains to ensure portability.

What practical benefit does Mohammed claim you gain by emulating hardware in QEMU (beyond being able to run without physical boards)?

A Emulation guarantees the same electrical and timing characteristics as the real device, so you never need physical testing.

B Emulating hardware forces you to translate the datasheet into software, which improves understanding and can reveal documentation errors or nuanced behaviors important for driver development.

C Emulation eliminates the need to write a device tree because QEMU invents one automatically.

D Emulation always runs faster than the real device, so debugging is quicker and more accurate.

E Emulation makes kernel APIs stable across versions so you don't need to worry about API changes.

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Upvotes Newest Oldest

ray

Score: 0 | 3 years ago | no reply

Hi may I know where we can obtain the config and dts files for the digi board?
I was under the impression that the instruction might be under Abstract but that does not seem to be the case

Tobi_Lifschitz

Score: 0 | 4 years ago | 1 reply

Hi Mohammed, thank you for the workshop. What benefits would you say using QEMU has, compared to using a development board to start developing a project, if cost is not a problem? Also, based on your experience, does it makes sense to use QEMU in more complex or simpler projects?

mabSpeaker

Score: 0 | 4 years ago | no reply

Hi,
Excellent questions! Usually, I use QEMU to test out a driver if I'm running into hardware issues on a custom board, or when I'm waiting for a component/part to arrive. When using a development board, the latter may be more of a reason to use QEMU. I would say it makes more sense to use QEMU for simpler projects, or tasks that are pretty localized, such as when working on a specific driver, kernel module, or kernel feature.

dcomer

Score: 0 | 4 years ago | 1 reply

I did not see the setup instructions. Where are they please?

KeithH_TX

Score: 0 | 4 years ago | no reply

Click into the [Abstract] tab above. see: This workshop has the following prerequisites:

Install Ubuntu >= 18.04 on your PC (either on bare-metal or as a VM):
Install qemu-system-arm (sudo apt-get install qemu-system-arm)
Install your favorite text editor (e.g. nano, vim)
Clone the buildroot repository on your Ubuntu installation by executing the following from the command line: $> git clone git://git.buildroot.net/buildroot
Clone the qemu repository on your Ubuntu installation by executing the following from the command line: $> git clone --depth 1 --branch v6.2.0 https://github.com/qemu/qemu.git
Clone the Linux kernel repository on your Ubuntu installation by executing the following from the command line: $> git clone --depth 1 --branch v5.17 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

dcomer

Score: 0 | 4 years ago | no reply

Never mind... :(

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