oasis os

x86 32-bit operating system built from scratch on i386 architecture.

This project includes C, assembly, and header files covering booting, protected mode, paging, multitasking, filesystem, syscalls, a C compiler, an assembler, and user mode execution.

component status

component	status	files
boot + gdt + idt	done	entry.asm, gdt.c, idt.c
drivers (vga, keyboard, timer, ata, pic)	done	vga.c, keyboard.c, timer.c, ata.c, pic.c, io.c
paging + pmm + heap	done	paging.c, pmm.c, heap.c
process isolation (per-task cr3)	done	paging.c, task_user.c
oafs filesystem (indirect + multi-block)	done	vfs.c, fd.c
syscall layer (ring 0 + ring 3)	done	syscall.c, interrupt.asm
task scheduler (round-robin, cr3 switching)	done	task.c
kernel heap (free-list, splitting, coalescing)	done	heap.c
occ compiler (int, for, if, while, params, array)	done	lexer.c, parser.c, codegen.c
built-in assembler (x86 32-bit, times, ext syms)	done	asm.c
user mode (ring 3, iret redirect, exit)	done	task_user.c, interrupt.asm
klibc (printf, scanf, etc for kernel mode)	done	klibc.c
usrlib (printf, malloc via syscall)	done	usrlib.c
logging (circular buffer, dmesg, auto-exception log)	done	log.c
shell + utilities (ls, cd, cat, write, echo, hexdump)	done	kernel.c
text editor (nano-like)	done	editor.c
boot screen (oasis os in center, loading dots)	done	kernel.c

build

sudo apt install gcc nasm grub2-common xorriso qemu-system-x86
make   # kernel.bin + oasis.iso
make run   # qemu-system-i386 -kernel kernel.bin

directory structure

src/
 boot/   entry.asm (entry point, 64kb stack), linker.ld
 kernel/
   core/    kernel.c (shell), gdt.c, paging.c, pmm.c, vga.c, memory.c (e820)
   drivers/ ata.c (pio), block.c (cache), idt.c (interrupt handler), io.c (port io)
            keyboard.c (ps/2), pic.c, timer.c (pit)
   fs/      fd.c (file descriptor), vfs.c (oafs inode-based)
   lib/     string.c, lexer.c, parser.c, codegen.c (occ compiler)
            klibc.c (kernel libc), heap.c (kmalloc), log.c, usrlib.c (user lib)
   syscall/ syscall.c (dispatcher), interrupt.asm (irq + syscall handler)
   tasks/   task.c (scheduler, tcb), task_user.c (ring 3 task creation)
   apps/    editor.c (text editor), asm.c (built-in assembler)
include/ kernel headers
docs/    documentation
Makefile
iso/     grub config + kernel.bin for iso image

memory layout

0x00000000 - 0x003FFFFF   identity map (kernel binary, bss, stack, page tables)
0x00400000 - 0x007FFFFF   reserved (kernel mapping extension)
0x00800000 - 0x00EFFFFF   user code space
0x00F00000 - 0x00FFFFFF   user stack (16kb per task)
0x01000000 - 0x01FFFFFF   user heap (brk, up to 16mb)
0x02000000 - 0x02FFFFFF   kernel heap (kmalloc arena, 16mb)
0x40000000                CODE_VIRT (assembler output, multi-page)
0xC0000000-0xC0400000     higher-half kernel mapping

gdt layout