LiOS

An experimental x86_64 operating system written from scratch in C.

Currently Implemented

• Bootstrapping to long mode
• Interrupts (only keyboard implemented)
• Printing to VGA graphical mode and serial
• Some basic memory management
  • Uses paging (obviously)
  • Linked list based page frame and virtual address allocator
  • Kernel heap allocator (using linked lists and bitmap)
• Supports UEFI

To Do

• CPUID stuff?
• Virtual address allocator can only use 1 4KiB page, which is only 128 linked list nodes. So if the memory gets too fragmented the allocator will completely break.
• Filesystem and hard disk/solid state drive driver
• Processes
• ELF program loading and userspace programs
• Userspace shell program

Memory Layout

Sort of based on Linux.

• 0xFFFFFFFF80000000-0xFFFFFFFFFFFFFFFF (highest 2GiB) is directly mapped to the first 2GiB of physical memory. Paging structures, and also DMA structures sometime in the future, are stored here.
• 0xFFFFF00000000000-0xFFFFFFFF80000000 are used for other pieces of kernel memory. Page frames come from the rest of physical memory, outside of the first 2GiB. User page frames also come from here.
• 0xFFFF800000000000-0xFFFFF00000000000 reserved for VGA frame buffer virtual address
• Lower-half virtual memory for user processes.

Sources

• OSTEP book
• Intel and AMD manuals
• QEMU docs
• Multiboot2 specification
• OSDev Wiki
• ACPI specification
• UEFI specification
• NVMe base specification and NVMe over PCIe specification (here)

(write bootable usb: sudo dd if=iso/os.iso of=/dev/sda)