How can I use Bochs to run Assembly code?

Question

I want to use Bochs as an 8086 emulator. Is there an easy way to do this? What I want is something like emu8086 (http://www.emu8086.com/).

Answer 1

sudo apt-get install bochs bochs-sdl

printf 'ata0-master: type=disk, path="main.img", mode=flat, cylinders=1, heads=1, spt=1
boot: disk
display_library: sdl
megs: 128
' > .bochsrc

bochs -q

worked for me on Ubuntu 14.04, Bochs 2.4.6 with a 512 byte long boot sector main.img.

• cylinders=1, heads=1, spt=1 specifies the disk size, and must match your image! Here we set everything to 1 to mean 1 cylinder, which is 512 bytes like our image file.
• display_library: sdl may be needed because of an Ubuntu packaging bug

main.img was generated from main.asm:

org 0x7c00
bits 16
cli
mov ax, 0x0E61
int 0x10
hlt
times 510 - ($-$$) db 0
dw 0xaa55

Then:

nasm -f bin -o main.img main.asm

This images uses the BIOS to print a single character a to the screen.

It is possible to avoid the creation of the .bochsrc file by using the following command line:

bochs \
    -qf /dev/null \
    'ata0-master: type=disk, path="main.img", mode=flat, cylinders=1, heads=1, spt=1' \
    'boot: disk' \
    'display_library: sdl' \
    'megs: 128'

The -qf /dev/null part is ugly, but it is the only way I've managed to automatically skip the menu screen:

• -q or -n always ask for it, and I have to hit 6 for it to run afterwards
• -qn <(echo ...) also worked, but uses a Bash extension which would fail on my Makefile

QEMU's interface was easier to get started with, so I recommend using it instead.

GitHub repository with this example: https://github.com/cirosantilli/x86-bare-metal-examples/blob/cba0757990843f412b14dffad45467ad0034d286/Makefile#L33