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@@ -1,136 +1,140 @@ -# Lume Operating System - -**Lume** is an experimental operating system kernel built from scratch for the **RISC-V 64** architecture. This project aims to explore the core implementation details of a modern Unix-like operating system. - -## π Current Status - -The project is currently deep in **Phase 2: Memory & Process Management**. - -The kernel has successfully transitioned from the bootloader to supervisor mode, enabled Sv39 virtual memory paging, and supports the execution of the first user-space process (`initcode`). It features basic process lifecycle management (creation, execution, termination, and reclamation). - -### β
Key Features Implemented - -* **Architecture Support** - * **Target**: RISC-V 64-bit (Sv39). - * **Modes**: Supervisor Mode (S-Mode) and User Mode (U-Mode). - * **Boot Flow**: OpenSBI -> Kernel Entry -> Main. - -* **Memory Management** - * **PMM (Physical Memory Management)**: Page frame allocator based on a free-list structure. - * **VM (Virtual Memory)**: Full Sv39 multi-level page table mapping. - * **Address Space**: - * **Kernel**: Higher-half mapping (Direct Mapping) + Trampoline. - * **User**: Independent page tables per process, containing code, data, stack, and trap pages. - * **Isolation**: `Trampoline` page mechanism for safe Kernel/User transitions. - -* **Process & Scheduling** - * **Process Model**: `struct Proc` (PCB) managing independent kernel stacks and trap frames. - * **Scheduling**: Preemptive Round-Robin scheduler driven by hardware timer interrupts. - * **Context Switching**: Assembly-level `swtch` logic to save/restore callee-saved registers. - * **Synchronization**: Spinlocks for protecting critical kernel data structures. - -* **System Calls** - A syscall dispatch framework (`ecall`) is established, currently supporting: - * `SYS_fork`: Create a child process (deep copy of memory and page tables). - * `SYS_exit`: Terminate the current process. - * `SYS_wait`: Wait for a child process to exit and reap resources. - * `SYS_write`: Write output to the console (currently direct via UART). - * `SYS_getpid`: Retrieve the current process ID. - * `SYS_putc`: Character output for debugging. - -* **Drivers** - * **UART**: Basic initialization and polled I/O for kernel logging. - -## π Project Structure - -```text -Lume/ -βββ src/ -β βββ boot/ # Bootloader code (entry.S) -β βββ kernel/ # Core kernel subsystems -β β βββ mm/ # Memory Management (pmm.cc, vm.cc) -β β βββ proc/ # Process Management (proc.cc, swtch.S) -β β βββ trap/ # Interrupt & Exception handling (trap.S, trampoline.S) -β β βββ syscall.cc # System call dispatcher -β β βββ main.cc # Kernel entry point -β β βββ ... -β βββ user/ # User-space programs (init.cc, usys.S) -β βββ drivers/ # Hardware drivers (uart.cc) -β βββ lib/ # Kernel utility libraries (string.cc) -βββ include/ # Header files -βββ Makefile # Build configuration -βββ link.ld # Kernel linker script -``` +# Lume OS +**A Lightweight, Educational RISC-V Operating System** +> Luminescence in the Deep Night -## π οΈ Build & Run -This project relies on the GCC RISC-V toolchain and QEMU emulator. +Lume OS is a 64-bit monolithic operating system kernel written in C++ for the RISC-V architecture. Currently designed for educational purposes and kernel hacking, the project is now evolving towards a Tiny Linux-Compatible Kernel capable of running standard Linux userspace binaries (musl libc, BusyBox, etc.) by implementing the Linux Syscall ABI. -### Prerequisites -Compiler: riscv64-linux-gnu-gcc / g++ +## π Build & Run -Emulator: qemu-system-riscv64 +### Prerequisites +* Toolchain: `riscv64-linux-gnu-g++` / `gcc` -Build Tool: make +* Emulator: `qemu-system-riscv64` -### Commands -1. **Compile Kernel & User Programs:** +* Build System: `make` +### Compiling ```Bash +# Compile kernel and user programs make all ``` -2. **Run in QEMU (No Graphic Mode):** +### Running in QEMU ```Bash +# Run the OS make run -``` -Expected Output: You will see kernel boot logs, page table initialization, and output from the first user process (`initcode`). -3. **Debug Mode (GDB):** - -```Bash +# Debug mode (attaches GDB) make debug ``` -This starts QEMU in a paused state, waiting for a GDB connection on port 1234. -4. **Clean Build Artifacts:** +## π System Architecture & Current Features +Based on the current source tree, Lume OS implements the following core subsystems: -```Bash -make clean -``` +### 1. Kernel Core & Hardware Abstraction +* Architecture: RISC-V 64-bit (Sv39 paging) targeting QEMU `virt` machine. + +* Boot: Device Tree (FDT) parsing for hardware discovery. + +* Concurrency: SMP (Symmetric Multi-Processing) support with per-CPU state management. + +* Traps: Supervisor-mode interrupt and exception handling. + +### 2. Memory Management +* Physical Memory: Buddy System allocator for page-level management. + +* Kernel Heap: SLAB allocator (`kmalloc`/`kfree`) for efficient object management. + +* Virtual Memory: Basic paging support. Current user process memory model is linear (heap grows contiguously via `sbrk`). + +### 3. Process Management +* Scheduling: Round-Robin scheduler with per-CPU runqueues and work stealing mechanisms. + +* Context Switching: Saves callee-saved registers; currently lacks FPU/Vector state saving. -## πΊοΈ Roadmap -* [x] Phase 1: Foundation +* Lifecycle: Basic `fork`, `exec`, `exit`, and `wait` system calls. - [x] UART Driver & Formatted Output. +### 4. File System & I/O +* VFS: A preliminary Virtual File System abstraction with `inode` polymorphism. - [x] Physical Memory Allocator (PMM). +* Filesystem: FAT32 implementation with basic read/write/create/delete support. - [x] Basic Interrupt Handling Framework. +* Buffer Cache: Block-level caching (Bio) coupled with the VirtIO driver. -* [x] Phase 2: Memory & Process (In Progress) +* Drivers: - [x] Virtual Memory (Sv39) & Kernel Page Tables. + * VirtIO: Block device driver (MMIO). - [x] User Address Space Construction. + * UART: 16550A-compatible serial console driver with line buffering. - [x] Preemptive Scheduler. + * PLIC: Platform-Level Interrupt Controller support. - [x] Basic System Calls (fork, exit, wait, write). +### 5. User Space +* Libc: A minimal custom C library (`ulib`) providing stdio (`printf`/`scanf`), stdlib (`malloc`/`free`), and string operations. - [ ] exec System Call (ELF Loader). +* Shell: A functional shell (`sh`) supporting pipes (`|`), redirection (`<`, `>`), and background execution (`&`). - [ ] sbrk for Dynamic Heap Growth. +* Utils: Standard Unix-like tools: `ls`, `cat`, `echo`, `mkdir`, `rm`, `touch`, `cp`, `mv`. -* [ ] Phase 3: File System & I/O (Planned) +## π Gap Analysis: Lume OS vs. Linux +To achieve the goal of binary compatibility with the Linux ecosystem, Lume OS is currently undergoing a major refactoring. The following table highlights the critical differences: - [ ] VirtIO Block Device Driver. +|Subsystem|Lume OS (Current)|Linux / Modern Goal|Gap & Impact| +|:------:|:---------:|:--------:|:---------:| +|Syscall ABI|Custom IDs & `-1` return codes|Standard RISC-V headers & `-errno`|Binaries compiled for Linux cannot run on Lume.| +|Memory Model|Linear `p->sz` (Heap only)|VMA (Virtual Memory Areas)|Cannot support `mmap`, memory gaps, or dynamic libraries (`.so`).| +|Binary Format|Static ELF only|Dynamic ELF (`PT_INTERP`)|Cannot run `ld.so` or shared libraries; high memory waste.| +|Threading|Single-threaded Processes|1:1 Threads (`clone` + NPTL)|Cannot support `pthreads` or modern concurrent apps.| +|Filesystem|Tightly coupled FAT32|VFS + Mount Points + Pseudo FS|Missing `/dev`, `/proc`, `/sys`; standard tools (`top`, `ps`) fail.| +|Signals|Basic `kill` flag|Full Signal Handling|No `Ctrl-C` handling, `SIGSEGV` recovery, or async notifications.| +|I/O Model|Synchronous/Blocking|Async/Non-blocking (`poll`/`epoll`)|Cannot support high-performance servers (e.g., Nginx).| - [ ] Virtual File System (VFS). +## πΊοΈ Roadmap to Linux Compatibility +We are executing a 4-phase plan to transform Lume OS into a Tiny Linux Clone. - [ ] File I/O System Calls (open, read, close). -* [ ] Phase 4: Waiting for you... +### Phase 1: Core Architecture Refactoring (The Foundation) +* [ ] VMA Implementation: Replace `sz` with `vm_area_struct` (RB-Tree/List) to support mmap and demand paging. + +* [ ] VFS 2.0: Decouple FAT32. Implement `struct mount`, `dentry` cache, and `RamFS`. + +* [ ] DevFS & ProcFS: Implement `/dev` and `/proc` mounting support. + +* [ ] Syscall Alignment: Renumber syscalls to match Linux RISC-V 64 ABI and standardize errno. + +### Phase 2: Runtime Environment +* [ ] ELF Interpreter: Support `PT_INTERP` to load dynamic linkers (`ld-musl-riscv64.so.1`). + +* [ ] Auxiliary Vector: Construct `AT_RANDOM`, `AT_PHDR`, etc., on the user stack. + +* [ ] New Syscalls: `brk`, `writev`, `readv`, `ioctl` (TTY), `getdents64`. + +### Phase 3: Advanced Process Features +* [ ] Threading: Implement `sys_clone` with `CLONE_VM` / `CLONE_THREAD`. + +* [ ] Synchronization: Implement `sys_futex` for userspace locking. + +* [ ] Signals: Implement `sigaction`, signal frame construction, and `sigreturn` trampoline. + +### Phase 4: Ecosystem & Networking +* [ ] Network Stack: Port lwIP and implement `virtio-net` driver. + +* [ ] Socket API: Implement `socket`, `bind`, `connect`, `poll`. + +* [ ] Userland: Port Musl Libc and BusyBox. ## π License -This project is open-source under the MIT License. See the LICENSE file for details. ------------- -Copyright (c) 2025 Richard Qin
\ No newline at end of file + +Lume OS is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation, either version 2 of the License, or +(at your option) any later version. + +Lume OS is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see <https://www.gnu.org/licenses/>. + +See the [LICENSE](LICENSE) file for details.
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