Melon OS

Unix like operating system on i386.

How to build

Simply run:

make

You will then see melonos.qcow2, melonfs.qcow2 being built.

To start in qemu

make qemu

To enable gdb debug mode

GDB=1 make qemu

To interact with the OS through serial IO

Run the following on one terminal

make serial

This will wait for qemu to start.

On another one run qemu.

# you can turn off qemu graphics like this
GRAPHICS=0 GDB=1 make qemu

Now you can handle IO through the serial.

To print realtime debug log

Make sure build with debug flag on

DEBUG=1 make

Then, on one terminal run

make debug

It will listen to qemu's debuggin output through COM2.

Then run

make qemu

as usual.

Now all the real time debugging info will be printed on the debug terminal.

How to debug

You can debug both the kernel and userpace program with gdb. The debugging output can be accessed via make debug as mentioned above.

To debug ther kernel, simply run DEBUG=1 make qemu and run gdb on another session. Once the gdb starts, run target remote localhost:1234. This connects the gdb with qemu. Then you can set a breakpoint like (gdb) b scheduler.

To debug a user space program, you need to load user program symbols to gdb as well. E.g, to debug the shell, once the gdb connects to the kernel, run (gdb) add-symbol-file melon/sh_. Then (gdb) b main. Note symbols in kernel and user program will be at the same namespace, if there is a conflict you need to delete the one you don't need.

You can use .gdbinit to automate the debugging process. E.g My .gdbinit always have the following line:

target remote localhost:1234

This auto-connects the gdb with qemu.

Design

This is a rough diagram for what's going on here.