sop overview

Introduction

sop is short for Sector OPerations. It's an overengineered x86 real mode BIOS bootsector (<=510 bytes) that implements a fully-working command line. sop is very extensible and easily hackable: you can add your own commands, make them run at boot, and alter the existing ones as well as internal behavior. All labels (aka function symbols) are public and can be monkeypatched and trampolined.

Features

This terminal-like interface supports:

• Text-mode screen assertion
• ASCII-only BIOS keyboard with backspace support
• One-way scrolling
• Clearing

The command-line enters a prompt loop in which commands can be ran. Out of the box, there are two supported commands which allow bootstrapping an enhanced shell:

• l is for load. Loads a sector into a given address.
  • Usage: l <.4 hex address> <.4 hex LBA>
  • Example: l 8000 0001
• c is for call. Performs a call to a given address.
  • Usage: c <.4 hex address>
  • Example: c 8000

How to use

Clone the repository and run make. This will generate sop.bin and symbols.txt.

• sop.bin contains sop; that is, the bootsector
• symbols.txt is a generated NASM source that addresses the labels (functions)

Have a look at what you can do first. If you have qemu installed, run make run.

Examples

Example extensions are available under examples/. The following ship with sop:

• helloworld, run with make runhelloworld, and execute l 8000 0001 and c 8000. Prints Hello world!.
• color, run with make runcolor, no need to execute anything. Adds a color command which behaves like DOS' one.
  • Usage: color 00<.2 hex color>
  • Example: color 00F1

sop development

If you want to develop an extension, copy examples/helloworld.asm and build on top of that.

Available functions

symbols.txt includes addresses for SOP labels. These are the most useful:

• printz prints a null-terminated string to screen
• print_char prints only one character
• clear clears the screen
• get_line gets a line from keyboard input (blocks)
• get_char gets only one character
• readsect loads a sector from disk into memory
• dapack_lba contains the LBA to load when you run readsect
• dapack_offset contains the addres into which to copy the sector

For usage reference and side-effects, check the comment on top of each function in sop's source.

Autoload

Extensions can be loaded automatically by sop if their first byte is 0x69.

• This can only happen with the first extension, the one located at disk's LBA #1.
• Unlike a regular sop extension, ret is not available, and one must jmp to SOP_cmd.