04.all-your-memory-belongs-to-us

Chapter 4: All your memory belongs to us

Examples

• hello.s -- example of direct access to text-mode memory.

• circles.s -- colorful circles.

• boot.s -- "Hello, world" program that can be used inside boot sector.

  Test the image using QEMU:

  $ qemu-system-x86_64 -fda boot.img
  

Instructions learned

1. cld, clear direction flag.
2. lds, load register and DS register.
3. les, load register and ES register.
4. sed, set direction flag.
5. stosb, store AL into ES:DI address. Increase DI by 1 (if direction flag is zero) or decrease DI by 1 (if direction flag is one).
6. stosw, store AX into ES:DI address. Increase DI by 2 (if direction flag is zero) or decrease DI by 2 (if direction flag is one).