Using old x86 hardware or QEMU to take control of CPU after Hard Reset. Overview of commonly used boot loaders , Preparing a custom message bootable USB stick and demo on x86-uboot with QEMU . It is discussed at https://youtu.be/F71LGSrj9cc blog: www.embedkari.com Embedded Career: www.facebook.com/embedkari

1. Copyright@Embedkari
QEMU
BIOS
U-Boot
UEFI

2. Agenda
●
QEMU or Quick EMUlator
●
Bootloader overview
●
X86 booting mechanism
●
BIOS to boot sector code transfer demo
●
U-Boot demo for x86 using QEMU

3. Disclaimer
●
Presenter will not be responsible for for any
damage to USB or HDD due to experiments
followed.
●
Take a note of all the instructions carefully
●
Don’t use your hard disk for bootloader
experiments.
●
Presenter will use either QEMU or old x86
based system

4. QEMU
●
QEMU is a generic open source machine emulator and
virtualizer
●
Emulates program written for one architecture in another
●
It can run virtual machines like KVM in host CPU
●
Installation
–
sudo apt install qemu-system
–
If error
–
sudo apt install qemu-system --fix-missing

5. Bootloader
●
BIOS →UEFI
●
8xxROM→PPCboot—Armboot merged--→U-boot
●
TianoCore
–
open source implementation of UEFI
●
LinuxBIOS-->Coreboot
●
Libreboot
●
Both Coreboot and Libreboot are aimed to replace
proprietary boot firmware

6. X86 booting mechanism
●
Hardware Reset
●
BIOS(Basic Input/Output System) or Platform Firmware in ASM
–
Resides in non-volatile memory and prepares all POST procedures
–
Interactive hardware configuration
–
Boot mode
●
UEFI / CSM(Compatibility Support Mode)/BIOS
●
Boot Loader
–
Extensible Firmware Interface (EFI)
–
Unified Extensible Firmware Interface(UEFI) written in C
●
Boot Partition Format
–
Boot loader support also depends on type of partition
●
MBR(Master Boot Record) disk partition
●
GPT(GUID Partion Table) disk partition

7. Custom boot.asm●
org 0x7C00 ;BIOS loads program here
●
bits 16 ;16-bit mode
●
start:
●
cli ;Disable Interrupts
●
mov si, welcm ;SI points to custom data
●
mov ah, 0x0E ; Tell BIOS to print characters
●
.loop lodsb ;load byte into AL
–
or al, al
–
jz halt
–
jmp .loop
●
halt: hlt
●
welcm: db “Embedkari Welcomes You! “
●
times 510 - ($ - $$) db 0 ;Fills remaining bytes except last two
●
dw 0xAA55

8. Custom boot sector
Experiment
●
nasm(Netwide Assembler) Open source s/w for x86
–
sudo apt update
–
Check and install build-essential if not present
–
sudo apt list | grep build | grep essential
–
sudo apt install nasm
●
nasm boot.asm -f bin -o boot.bin
●
You may verify assembly listing using
–
nasm boot.asm -l boot.lst
●
Check the binary in QEMU
●
qemu-system-i386 -fda boot.bin

10. Program boot.bin to USB
●
USB data can be
verified if required
●
Start Cygwin as
adminstrator
●
dd if=/dev/sdb bs=512
count=4 of=test.bin

11. U-Boot-x86 @QEMU
●
git clone git://git.denx.de/u-boot-x86.git
●
cd u-boot-x86
●
export BUILD_ROM=y
●
make qemu-x86_defconfig
●
make all
●
Test U-boot in QEMU
●
qemu-system-i386 -nographic -bios u-
boot.rom -net nic -net user,tftp=/tftpboot

12. U-Boot build issue
●
You may get error due to absence of required
Libraries and this may lead to following additional
installation
●
For missing swig
–
sudo apt install swig
●
For Python 2
–
sudo apt install python-dev
●
For Python 3
–
sudo apt install python3-dev

13. Reference
●
https://firmware.intel.com/learn/uefi/about-uefi
●
http://www.uefi.org/
●
https://www.qemu.org/
●
https://manpages.debian.org/stretch/qemu-system-
●
https://pci-ids.ucw.cz/read/PC/8086
●

14. THANKS
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