Ambroxol

Funny MBR experiments

Builder

Use ./builder to transform an opcode file with comments like this:

# Simple example

45 46 49 20 50 41 52 54  # First line
00 00 01 00              # Second line

# Comment
00 00 01 00              # Third line
27 6D 9F C9              # Yet another line

into plain binary file:

$ ./build example.mbr sector.bin
$ xxd sector.bin                
00000000: 4546 4920 5041 5254 0000 0100 0000 0100  EFI PART........
00000010: 276d 9fc9                                'm..

Loaders

A simple string printer in the printer.mbr

printer.mbr is a simple example of the MBR code execution.

File contains:

• A fixed string at 0x0080 that will be print
• A binary code (x86 opcodes) with a loop extracting characters from data block and printing it using INT 10h BIOS function.

A not very simple printer in the color-printer.mbr

Improves:

• Changes a video mode to use colored output
• String printing in the infinite loop
• (New!) String changing a color!

A useless typewriter in the typewriter.mbr

typewriter.mbr contains an example of the keyboard input processing.

It can:

• Print pressed characters in a loop.
• Process a Return/Enter key to create a new line.
• Process a Backspace key to return to previous character (except new line :)) and replace it with another one.

Usage

How to build

$ ./build printer.mbr printer.img && stat -f %z printer.img
512

512 -- is a valid MBR size. Otherwise you've got a corrupted file :(

How to test

You need to use QEMU or any other emulator or VM able to use .img or .bin disk images.

$ qemu-system-i386 -nic none printer.img

-nic none option disables network interfaces

How to use on hardware

Just write a USB-drive using dd:

$ dd if=printer.mbr of=/dev/sdb

Of course you need to find a valid path of your USB-drive.

Of course you have not to use partition path (e. g. /dev/sdb1) instead of devices path.

Then plug a drive into your x86-compatible device and boot it using USB.