os-dev-scratch

사용 방법

설치 명령을 복사하고 자신의 에이전트 환경에 설치하기 전에 소스 패키지를 확인하세요.
필요한 도구, 인증 정보, 지원 환경은 원본 문서에서 확인하세요.
입력과 원하는 산출물을 설명하고 출처와 결과를 대조하세요.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill os-dev-scratch

시작 전 확인

설치에는 모델 구독, API 한도, 파일 접근 권한이 포함되지 않습니다.
별점 수와 설치 수는 활동 지표이며 독립적인 품질·보안 검증이 아닙니다.

원본 Skill 문서

원본 저장소의 제목, 예시, 코드, 표, 링크, 이미지를 유지해 표시합니다.

OS Development from Scratch

Purpose

Guide agents through building a minimal operating system from scratch: bootloader stages (BIOS/GRUB vs UEFI/limine), 64-bit long mode setup with GDT and page tables, IDT and interrupt handlers, PIC/APIC configuration, basic keyboard and serial drivers, physical and virtual memory managers, context switching, with xv6-RISC-V as a reference architecture.

When to Use

Learning how an OS boots from power-on to main()
Implementing protected/long mode transitions on x86-64
Writing a physical memory allocator (bitmap) and page table manager
Handling timer, keyboard, and page fault interrupts
Testing with QEMU -kernel and cross-compiler x86_64-elf-gcc
Porting concepts from xv6 to a custom x86 or RISC-V kernel

Workflow

1. Boot stages overview

BIOS path (legacy)
├── BIOS POST
├── MBR (512 bytes) → boot sector loads stage2
├── GRUB/multiboot → loads kernel ELF
└── kernel entry (_start)

UEFI path (modern)
├── UEFI firmware
├── EFI bootloader (limine, systemd-boot)
├── Loads kernel + initrd from ESP
└── kernel entry (handoff with memory map)

2. Toolchain setup

bash

# Cross-compiler for bare metal
brew install x86_64-elf-gcc x86_64-elf-binutils   # macOS
# or build from source / apt install gcc-x86-64-elf

x86_64-elf-gcc --version

# QEMU for testing
qemu-system-x86_64 --version

Linker script essentials:

/* linker.ld */
ENTRY(_start)
SECTIONS {
    . = 0x100000;          /* 1MB — typical kernel load address */
    .text : { *(.text .text.*) }
    .rodata : { *(.rodata .rodata.*) }
    .data : { *(.data .data.*) }
    .bss : { *(.bss .bss.*) }
}

bash

x86_64-elf-gcc -ffreestanding -nostdlib -c kernel.c -o kernel.o
x86_64-elf-ld -T linker.ld kernel.o -o kernel.elf

3. Multiboot/limine boot

bash

# QEMU direct kernel boot (no disk)
qemu-system-x86_64 \
  -kernel kernel.elf \
  -serial stdio \
  -m 128M \
  -no-reboot -no-shutdown

# With limine (UEFI)
qemu-system-x86_64 \
  -bios /usr/share/ovmf/OVMF.fd \
  -drive file=disk.img,format=raw \
  -serial stdio

4. Long mode setup

Protected mode (32-bit) → enable PAE → setup 4-level page tables → enable long mode

// Minimal GDT entry (64-bit flat segments)
struct gdt_entry {
    uint16_t limit_low;
    uint16_t base_low;
    uint8_t  base_mid;
    uint8_t  access;
    uint8_t  granularity;
    uint8_t  base_high;
} __attribute__((packed));

// Page table setup (4KB pages, identity map first 1GB)
uint64_t pml4[512] __attribute__((aligned(4096)));
uint64_t pdpt[512] __attribute__((aligned(4096)));
uint64_t pd[512] __attribute__((aligned(4096)));

void setup_paging(void) {
    for (int i = 0; i < 512; i++)
        pd[i] = (i * 0x200000) | 0x83;  // 2MB huge pages
    pdpt[0] = (uint64_t)pd | 0x03;
    pml4[0] = (uint64_t)pdpt | 0x03;
    __asm__ volatile("mov %0, %%cr3" :: "r"(pml4));
}

5. IDT and interrupt handlers

struct idt_entry {
    uint16_t offset_low;
    uint16_t selector;
    uint8_t  ist;
    uint8_t  type_attr;
    uint16_t offset_mid;
    uint32_t offset_high;
    uint32_t zero;
} __attribute__((packed));

// ISR stub (assembly) → common handler → dispatch by vector
void interrupt_handler(struct trap_frame *frame) {
    if (frame->vector == 14)  // page fault
        handle_page_fault(frame->cr2, frame->error_code);
    else if (frame->vector == 33)  // keyboard IRQ remapped
        keyboard_handler();
}

bash

# Test page fault
# QEMU monitor: info registers

6. PIC and APIC

// Legacy PIC remapping (8259)
// Remap IRQ 0-15 to vectors 32-47
outb(0x20, 0x11); outb(0xA0, 0x11);
outb(0x21, 0x20); outb(0xA1, 0x28);  // vector offsets
// ...

// Modern: use APIC/IOAPIC (ACPI MADT parsing)
// LAPIC timer for preemption

7. Serial and keyboard drivers

// COM1 serial (0x3F8)
void serial_putc(char c) {
    while ((inb(0x3F8 + 5) & 0x20) == 0);
    outb(0x3F8, c);
}

// PS/2 keyboard scancode → ASCII lookup table
void keyboard_handler(void) {
    uint8_t scancode = inb(0x60);
    char c = scancode_to_ascii[scancode];
    if (c) serial_putc(c);
    outb(0x20, 0x20);  // EOI to PIC
}

bash

qemu-system-x86_64 -kernel kernel.elf -serial stdio
# printk output appears in terminal

8. Physical memory manager

// Bitmap allocator over usable RAM regions
// From multiboot memory map or UEFI memory map
#define PAGE_SIZE 4096
uint8_t *frame_bitmap;
uint64_t total_frames;

uint64_t alloc_frame(void) {
    for (uint64_t i = 0; i < total_frames; i++) {
        if (!test_bit(frame_bitmap, i)) {
            set_bit(frame_bitmap, i);
            return i * PAGE_SIZE;
        }
    }
    return 0;  // OOM
}

9. Context switching

struct context {
    uint64_t rax, rbx, rcx, rdx, rsi, rdi, rbp, rsp;
    uint64_t r8, r9, r10, r11, r12, r13, r14, r15;
    uint64_t rip;
};

void switch_context(struct context *old, struct context *new);
// Assembly: save callee-saved regs to old, restore from new, ret to new->rip

Cooperative scheduling first; add timer IRQ preemption later.

10. xv6-RISC-V reference

bash

git clone https://github.com/mit-pdos/xv6-riscv
cd xv6-riscv && make qemu

xv6 component	x86 equivalent
`kernel/vm.c`	Page table management
`kernel/trap.c`	IDT/interrupt dispatch
`kernel/proc.c`	Context switch, scheduler
`kernel/plic.c`	PIC/APIC interrupt controller
`user/usys.pl`	System call stubs

Common Problems

Symptom	Cause	Fix
Triple fault on boot	Invalid GDT/IDT or stack	Set up stack before enabling interrupts
QEMU black screen	No serial output configured	`-serial stdio`; early `serial_init`
Page fault in kernel	Unmapped address	Identity-map kernel; check CR3
IRQ never fires	PIC mask or IDT not loaded	`lidt`; unmask IRQ in PIC
Timer doesn't tick	LAPIC not initialized	Parse ACPI; calibrate LAPIC timer
Linker relocation error	Wrong load address	Match `linker.ld` with bootloader expectation

Related Skills

skills/low-level-programming/assembly-x86 — x86-64 assembly for ISR stubs
skills/low-level-programming/assembly-riscv — xv6-RISC-V reference ISA
skills/platform/riscv-privileged — RISC-V trap handling and page tables
skills/virtualization/qemu-kvm — QEMU flags for kernel development
skills/kernel/kernel-internals — Linux implementation of these concepts
skills/low-level-programming/linux-kernel-modules — graduate to Linux once basics work

사용 방법

시작 전 확인

OS Development from Scratch

Purpose

When to Use

Workflow

1. Boot stages overview

2. Toolchain setup

3. Multiboot/limine boot

4. Long mode setup

5. IDT and interrupt handlers

6. PIC and APIC

7. Serial and keyboard drivers

8. Physical memory manager

9. Context switching

10. xv6-RISC-V reference

Common Problems

Related Skills

관련 작업

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os-dev-scratch

사용 방법

시작 전 확인

OS Development from Scratch

Purpose

When to Use

Workflow

1. Boot stages overview

2. Toolchain setup

3. Multiboot/limine boot

4. Long mode setup

5. IDT and interrupt handlers

6. PIC and APIC

7. Serial and keyboard drivers

8. Physical memory manager

9. Context switching

10. xv6-RISC-V reference

Common Problems

Related Skills

관련 작업

rea-analysis-optimization

wizard

context-budget

docker-patterns

더 많은 Skills

core-dumps

custom-allocators

ebpf

flamegraphs