X-Git-Url: https://scm.lunaixsky.com/lunaix-os.git/blobdiff_plain/e6dbd781772925dfc07b2facfa0a1350e756ad8f..9e622bd093f8e106b7e8a00f55620f13cc5cd87f:/README.md

diff --git a/README.md b/README.md
index ebaf251..fe73edc 100644
--- a/README.md
+++ b/README.md
@@ -3,118 +3,323 @@
 </p>
 
 <p align="center">
-  <span>简体中文</span> | <a href="docs/README_en.md">English</a>
+  <a href="docs/README.cn.md">简体中文</a> | <a href="#the-lunaixos-project">English</a>
 </p>
 
-# LunaixOS Project 
-LunaixOS - 一个简单的，详细的，POSIX兼容的（但愿！），带有浓重个人风格的操作系统。开发过程以视频教程形式在Bilibili呈现：[《从零开始自制操作系统系列》](https://space.bilibili.com/12995787/channel/collectiondetail?sid=196337)。
+# The Lunaix Project
+
+The Lunaix kernel (or soon-to-be LunaixOS) is a hobby kernel, written entirely from scratch. Designed to be POSIX-compliance, performance critical and modern, with some independent thoughts being applied in architectural design.
+
+
+This project is built entirely from first principles - meaning no code was copy-pasted or recycled from other OS projects or tutorials. Lunaix didn't begin as an attempt to outperform anything; it started as a personal challenge to learn OS theory and explore advanced kernel features through original design and implementation. Everything you see here was developed solo, part-time, with only hardware specs and my beloved **Modern Operating Systems** as guidance.
+
+If you're a kernel hobbyist looking for a fresh take or tired of mass-produced projects, then welcome, you're in the right place!
+
+
+| ![showcase_lunaix-over-serial.png](docs/img/showcase_lunaix-over-serial.png) |
+|:--:|
+| *Lunaix over serial* (`console=/dev/ttyS0`) |
+
+| ![showcase_lunaix-over-serial.png](docs/img/showcase_lunaix-over-vga-text.png) |
+|:--:|
+| *Lunaix over VGA text mode* (`console=/dev/ttyVCON0`) |
+
+> By the way, do you know there is an online video course  by the author on the design of lunaix? [Check it out](https://space.bilibili.com/12995787/channel/collectiondetail?sid=196337) (although it is in Chinese!)
+
+## Features
+
+Lunaix is a multi-architecture, general-purpose kernel built with performance, modularity, and robustness in mind. Its design emphasizes advanced abstractions, proactive error detection, and subsystem isolation. Lunaix is
+
++ **Fully-preemptive** for responsive multi-tasking
++ **Modular** with compile-time configurable components and extensible subsystems
++ **High-performance**, leveraging modern caching strategies and efficient infrastructures.
++ **Fault-tolerant**, with built-in error handling and stack backtracing
++ **Robust by design**, using mechanisms like proactive deadlock detection and driver isolation
+
+A significant amount of effort has gone into crafting clean abstractions, implementing advanced kernel features, and applying performance optimizations throughout the system.
+
+To better illustrate the scope of work already done, the following non-exhaustive list outlines currently supported features in Lunaix:
+
+<details>
+
+<summary>List of all features implemented</summary>
+
++ Multi-ISA
+  + x86_32
+  + x86_64
+  + Aarch64 (WIP)
++ Boot protocol
+  + abstraction for different protocol
+  + configurable kernel boot-time parameters
++ Platform resource management and definition
+  + read-only ACPI table interpretation
+  + full devicetree implementation
++ Memory management
+  + architecture-neutral abstraction
+  + highmem
+  + copy-on-write
+  + page sharing
+  + explicit huge page
+  + on-demand paging
+  + compound page
+  + reverse mapping (rmap)
+  + memory compaction (WIP)
+  + slab-style object allocator
+  + inter-process address space access
++ Multi-tasking
+  + fully preemptive
+  + protection levels
+  + process isolation
+  + native threading
+  + signal mechanism
+  + round-robin scheduler (for now)
+  + kernel level multi-tasking (i.e. kernel threads)
+  + taskfs: file system interface to process and threads
++ File system
+  + POSIX-compliant interface
+  + virtual file system framework
+  + file system mounting mechanism
+  + page cache for file IO
+  + inode/dnode caching
+  + ext2 (rev.0, rev.1)
+  + iso9660 (rock-ridge)
+  + twifs: kernel state fs interface.
++ Device management and interrupt handling
+  + unified IRQ framework
+  + unified driver framework for heterogenous devices
+  + modular driver model allow compiled-time toggling
+  + asynchronous operation model supported
+  + devfs: device fs interface.
++ Block I/O (blkio)
+  + unified block IO interface
+  + IO request packets caching
+  + asynchronous IO operation
++ Serial I/O
+  + POSIX-compliant serial IO model
++ Caching Infrastructure
+  + LRU replacement policy and pooling
+  + kernel daemon for dynamic and transparent cache managements
++ Error handling and detection
+  + stack backtracing with symbol resolution
+  + stack unwinding for nested exception
+  + CPU state dumping
+  + deadlock/hung-up detection
+
+</details>
+
+<details>
+
+<summary>List of currently supported device</summary>
+
++ Architecture Neutral
+  + UART 16650-compatible driver
+  + Serial ATA AHCI
+  + PCI 3.0
+  + PCIe 1.1
+  + Standard VGA
++ Intel x86
+  + RTC (Intel PCH)
+  + IOAPIC IRQ controller
+  + APIC Timer
+  + Legacy i8042 keyboard controller
++ ARM
+  + GICv3
+  + PL011 (WIP)
+</details>
+
+## Project Structure
+
+| Path | Description |
+|-----|------|
+| [lunaix-os](../lunaix-os/) | LunaixOS source code |
+| [slides](../slides/) | Slides used in my videos |
+| [reference-material](../reference-material/)| References |
 
-## 当前进度以及支持的功能
+## Compile and Build
 
-该操作系统支持x86架构，运行在保护模式中，采用宏内核架构，目前仅支持单核心。内存结构采用经典的3:1划分，即低3GiB为用户地址空间（0x400000 ~ 0xBFFFFFFF），内核地址空间重映射至高1GiB（0xC0000000 ~ 0xFFFFFFFF）。内存的详细布局可参考[LunaixOS内存地图](docs/img/lunaix-os-mem.png)
+Building lunaix is simple, no more bloated dependencies to install, basic `build-essentials` installation plus a python are sufficient.
 
-在下述列表中，则列出目前所支持的所用功能和特性。列表项按照项目时间戳进行升序排列。
++ gcc (recommend v12+)
++ binutils
++ make
++ python (recommend v3.11+)
 
-+ 使用Multiboot进行引导启动
-+ APIC/IOAPIC作为中断管理器和计时器
-+ ACPI
-+ 虚拟内存
-+ 内存管理与按需分页（Demand Paging）
-+ 键盘输入
-+ 多进程
-+ 40个常见的Linux/POSIX系统调用（[附录1](#appendix1)）
-+ 用户模式
-+ 信号机制
-+ PCI 3.0
-+ PCIe 1.1 (WIP)
-+ Serial ATA AHCI
-+ 文件系统 (WIP)
+And also one should have environment variable `ARCH=<arch>` exported, where `<arch>` is one of the supported arhcitecture (`x86_32`, `x86_64`, `aarch64`).
 
-## 目录结构
+For cross compilation, also export `CX_PREFIX` to the gcc prefix for the corresponding `<arch>`.
 
-| | |
-|-----|------|
-| [lunaix-os](lunaix-os/) | LunaixOS源代码 |
-| [slides](slides/) | 视频中所用的幻灯片和补充材料 |
-| [reference-material](reference-material/)| 标准，技术文档和参考文献 |
+The following `make` actions are then available to use.
 
-## 编译与构建
+| Make command | Usage |
+| ---- | ---- |
+| `make all`               | Build the kernel bin |
+| `make rootfs`            | Build the stock rootfs |
+| `make clean`             | clean |
+| `make config`            | menuconfig |
 
-构建该项目需要满足以下条件：
+A successful build will give `build/bin/kernel.bin`.
 
-+ gcc (目标平台: i686-elf)
-+ binutils
-+ make
-+ xorriso
-+ grub-mkrescue
+**Please note: this is the kernel, not a bootable image, it require a bootloader to boot and specify the rootfs.**
 
-**注意：gcc不能是本机自带的，必须要从源码编译，并配置目标平台为：`i686-elf`，以进行交叉编译。配置过程可参考[附录二：编译gcc作为交叉编译器](#appendix2)。**
+## Get Started
 
-假若条件满足，那么可以直接执行`make all`进行构建，完成后可在生成的`build`目录下找到可引导的iso。
+If you are impatient, or just want something to run and don't want to went through tedious process of configuring rootfs and tweak kernel parameters. You can use the `live_debug.sh` provided in the lunaix root directory to quickly bring up the system with default parameters (also used by the author for debugging).
 
-本项目支持的make命令：
-| 命令 | 用途 |
-|---|---|
-| `make all` | 构建镜像（`-O2`） |
-| `make all-debug` | 构建适合调试用的镜像（`-Og`） |
-| `make run` | 使用QEMU运行build目录下的镜像|
-| `make debug-qemu` | 构建并使用QEMU进行调试 |
-| `make debug-bochs` | 构建并使用Bochs进行调试 |
-| `make debug-qemu-vscode` | 用于vscode整合 |
-| `make clean` | 删除build目录 |
+### Quick Start
 
-## 运行以及Issue
+This will get you up and running real quick. We will use `x86_64` as example.
 
-运行该操作系统需要一个虚拟磁盘镜像，可以使用如下命令快速创建一个：
+Assuming a Linux or other Unix-like shell environment.
+
+#### Select your target
+```sh
+$ export ARCH=x86_64
+```
 
-```bash
-qemu-img create -f vdi machine/disk0.vdi 128M
+#### Check Python
+```sh
+$ python --version
 ```
 
-如果你想要使用别的磁盘镜像，需要修改`configs/make-debug-tool`
+Ensure at least `3.11`
 
-找到这一行：
+#### Check compiler
+```sh
+$ gcc -dumpmachine
 ```
--drive id=disk,file="machine/disk0.vdi",if=none \
+
+Ensure `x86_64-linux-gnu` or anything resemble `x86_64`
+
+#### Check QEMU
+```sh
+$ which qemu-system-x86_64
 ```
 
-然后把`machine/disk0.vdi`替换成你的磁盘路径。
+Should display a valid installation path
+
+#### Optional: Setting up Cross-Compiler
+```sh
+$ export CX_PREFIX=x86_64-linux-gnu-
+```
 
-有很多办法去创建一个虚拟磁盘，比如[qemu-img](https://qemu-project.gitlab.io/qemu/system/images.html)。
+#### Run Configuration
+```sh
+make config
+```
 
-在大多数情况下，我都会尽量保证本机运行无误后，push到仓库中。同时，该系统是经过本机测试，能够在Bochs，QEMU (`= 7.0`)，VirtualBox下正常的运行（暂时没试过真机）。如果发现在使用`make all`之后，虚拟机中运行报错，则一般是编译器优化问题。这个问题笔者一般很快就会修复，如果你使用别的版本的gcc（笔者版本11.2），出现了此问题，欢迎提issue。请参考[附录3：Issue的提交](#appendix3)
+Then hitting `q` in the interactive shell to save and quit
 
-下面列出一些可能会出现的问题。
+#### Build stock rootfs
 
-#### 问题#1： QEMU下8042控制器提示找不到。
+```sh
+make rootfs
+```
 
-这是QEMU配置ACPI时的一个bug，在7.0.0版中修复了。
+#### Build & Run
+```sh
+./live_debug.sh
+```
 
-#### 问题#2：多进程运行时，偶尔会出现General Protection错误。
+you should see gdb now take control of your shell
 
-这很大概率是出现了竞态条件。虽然是相当不可能的。但如果出现了，还是请提issue。
+#### Connect to serial via telnet
 
-#### 问题#3：Bochs运行时，提示找不到AHCI控制器
+Open up another window or session
+```sh
+telnet localhost 12345
+```
 
-正常，**因为Bochs不支持SATA**。请使用QEMU或VirtualBox。
+#### Commence simulation
 
-#### 问题#4：键盘的上下方向键（用于滚屏）在VirtualBox下有时不好使
+Back to the gdb session and type `c` to countine
 
-可以试试`Shift+<方向键>`，这个问题的解决需要重写键盘驱动的状态机。我会找时间去做，毕竟这不是燃眉之急。
 
-## 参考教程
+#### Watch Lunaix booting!
 
-**没有！！** 本教程以及该操作系统均为原创，没有基于任何市面上现行的操作系统开发教程，且并非是基于任何的开源内核的二次开发。
+Congrats, enjoy your lunaix! (or submit an issue)
 
-为了制作LunaixOS，作者耗费大量时间和精力钻研技术文档，手册，理论书籍以及现行工业标准，从而尽量保证了知识的一手性。（这样一来，读者和听众们也算是拿到了二手的知识，而不是三手，四手，甚至n手的知识）。
 
-大部分的文档和标准可以在上述的[reference-material](reference-material/)中找到。
+### Not so Quick Start
+
+Here is a slower and yet more verbose steps:
+
+1. Select an architecture `<arch>`
+2. Check the compilation prerequisites and presence of `qemu-system-<arch>`
+3. Optionally export `CX_PREFIX` if you are building for another architecture.
+4. Run `make ARCH=<arch> rootfs` to build stock rootfs image, require support of `dd`，`mkfs.ext2`, `mount -o loop`, `mktemp`.
+5. Run `ARCH=<arch> live_debug.sh` to boot in QEMU with gdb hooked (one should see a gdb session)
+6. telnet to `localhost:12345`, this is QEMU emulated serial port
+7. type `c` in the active gdb session and commence emulation.
+8. Congrats, enjoy your lunaix!
+(or submit an issue)
+
+
+## Booting the kernel
+
+Since lunaix is a kernel, much like linux. It requires additional setup to do the magic. And, as in "much like linux", methods to make linux kernel boot can also apply to lunaix without or with little translation, as we will discuss below.
+
+The bootloader part is generic, any bootloader, for example GRUB will work (not tested for UEFI, but I expect this would be an exception), or booting up in QEMU using `-kernel` option
+
+The kernel command line, is however, a bit differentiated.
+The syntax is similar, both takes form of space-separated array of `<key>=<val>` pairs or boolean `<flag>`.
+
+Currently, lunaix support the following options
+
+| Option | Default Value | Optional | Usage |
+| ------ | ----          |  -----   | ----  |
+| console | `/dev/ttyS0`   | No | Specify the system console device, path within lunaix's devfs |
+| rootfs | `/dev/block/sda` | No | Specify the device contain rootfs image, path within lunaix's devfs |
+| init | `/init` | Yes | Path within rootfs of the `init` |
+
+
+## Submit an Issue
+
+If one ran into bug, one can submit an issue by filling up the following template
+
+```
+1. Describe the problem
+    "How does it look like, anything descriptive: visual, sonic, emotional experience"
+
+2. Steps to reproduce
+    "How you ran into this mess?"
 
-当然，您也可以参考以下列表来了解现阶段的LunaixOS都使用了哪些资料（本列表会随着开发进度更新）：
+3. Expected behaviour
+    "What do you intended/expected to achieve/to be"
 
-#### 手册，标准，技术文档
-+ [Intel 64 and IA-32 Architecture Software Developer's Manual (Full Volume Bundle)](https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html)
-+ [ACPI Specification (version 6.4)](https://uefi.org/sites/default/files/resources/ACPI_Spec_6_4_Jan22.pdf)
+4. Lunaix's panic trace (if applicable)
+
+5. Other clues that you think might be helpful
+```
+
+
+## Limitations
+
+The development process is still in motion, any limitation can be categorised as a feature yet to be. However, some features that the author considered to be the most urgent and wish the matters to be discussed.
+
+Lunaix is under impression of uniprocessor and not capable of running in SMP environment. This is major held back of being a modern operating system. It has the highest priority among all other tasks
+
+Lunaix do not have a mature (or even, an infant) user space ecosystem, mainly because the lack of a proper and sophisticated libc. Efforts need to be done for porting one to the target. However, given the author's tight schedule, this task is unfortunately still beyond the horizon.
+
+## Acknowledgement
+
+Albeit one must realise that the author has mentioned it in the very beginning, the author would like to emphaise **again** on the nature of this project.
+
+As a personal challenge, this project is independently developed by the author single-handly, which means:
+
++ No reference to existing tutorials, books, online courses or any open source project that might provide any example, hint or working prototype on the design and implementation of kernel, subsystems or anythings that can be contributed towards a working prototype.
++ The author has no prior knowledge on Linux kernel through out 90% of the project time.
++ All knowledge on the kernel design is coming from the basic textbook on operating system theory, that is, *Modern Operating System* by Tanenbaum.
++ All knowledge on the system programming is coming from the basic textbook, that is, *Computer System - A Programmer's Perspective Third Edition*
++ All knowledge on the generic framework design and driver development are ingested from various technical specifications gathered across the Internet.
+
+## References
+
++ Intel 64 and IA-32 Architecture Software Developer's Manual (Full Volume Bundle)
++ ACPI Specification (version 6.4)
++ Devicetree Specification
++ ARM® Generic Interrupt Controller (v3)
++ Arm® Architecture Reference Manual (Profile-A)
++ Procedure Call Standard for the Arm® 64-bit Architecture (AArch64)
 + IBM PC/AT Technical Reference
 + IBM VGA/XGA Technical Reference
 + 82093AA I/O Advanced Programmable Controller (IOAPIC) (Datasheet)
@@ -124,31 +329,24 @@ qemu-img create -f vdi machine/disk0.vdi 128M
 + PCI Express Base Specification, Revision 1.1
 + PCI Firmware Specification, Revision 3.0
 + Serial ATA - Advanced Host Controller Interface (AHCI), Revision 1.3.1
-+ Serial ATA: HIgh Speed Serialized AT Attachment, Revision 3.2
++ Serial ATA: High Speed Serialized AT Attachment, Revision 3.2
 + SCSI Command Reference Manual
 + ATA/ATAPI Command Set - 3 (ACS-3)
-
-**免责声明：PCI相关的标准最终解释权归PCI-SIG所有。此处提供的副本仅供个人学习使用。任何商用目的须向PCI-SIG购买。**
-
-#### 理论书籍
-+ *Computer System - A Programmer's Perspective Third Edition (CS:APP)* (Bryant, R & O'Hallaron, D)
++ ECMA-119 (ISO9660)
++ Rock Ridge Interchange Protocol (RRIP: IEEE P1282)
++ System Use Sharing Protocol (SUSP: IEEE P1281)
++ Tool Interface Standard (TIS) Portable Formats Specification (Version 1.1)
++ *Computer System - A Programmer's Perspective Third Edition* (Bryant, R & O'Hallaron, D), a.k.a. CS:APP
 + *Modern Operating System* (Tanenbaum, A)
-+ 《汇编语言》（王爽） - 用于入门Intel语法的x86汇编（对于AT&T语法，推荐阅读CS:APP）
-+ ~~《微机原理与接口技术》 - 用于大致了解x86架构的微机体系（更加细致的了解可以阅读Intel Manual）~~ （已过时，推荐阅读CS:APP）
++ Free VGA, http://www.osdever.net/FreeVGA/home.htm 
++ GNU CC & LD online documentation.
++ PCI Lookup, https://www.pcilookup.com/
++ Linux man pages
 
-#### 网站
-+ [OSDev](https://wiki.osdev.org/Main_Page) - 杂七杂八的参考，很多过来人的经验。作者主要用于上古资料查询以及收集；技术文献，手册，标准的粗略总结；以及开发环境/工具链的搭建。
-+ [FreeVGA](http://www.osdever.net/FreeVGA/home.htm) - 98年的资源！关于VGA编程技术的宝藏网站。
-+ GNU CC 和 GNU LD 的官方文档。
-+ [PCI Lookup](https://www.pcilookup.com/) - PCI设备编号查询
+## Appendix 1: Supported System Call<a id="appendix1"></a>
 
-#### 其他
-+ Linux Manual - 用于查询*nix API的一些具体行为。
+**Unix/Linux/POSIX**
 
-
-## 附录1：支持的系统调用<a id="appendix1"></a>
-
-### Unix/Linux/POSIX
 1. `sleep(3)`
 1. `wait(2)`
 1. `waitpid(2)`
@@ -186,91 +384,67 @@ qemu-img create -f vdi machine/disk0.vdi 128M
 2. `chdir(2)`
 2. `fchdir(2)`
 2. `getcwd(2)`
-2. `rename(2)`
+2. `rename(2)`※
 2. `mount(2)`
 2. `unmount` (a.k.a `umount(2)`)
-
-### LunaixOS自有
+2. `getxattr(2)`※
+2. `setxattr(2)`※
+2. `fgetxattr(2)`※
+2. `fsetxattr(2)`※
+2. `ioctl(2)`
+2. `getpgid(2)`
+2. `setpgid(2)`
+2. `mmap(2)`
+2. `munmap(2)`
+2. `execve(2)`
+3. `poll(2)` (via `pollctl`)
+3. `epoll_create(2)` (via `pollctl`)
+3. `epoll_ctl(2)` (via `pollctl`)
+3. `epoll_wait(2)` (via `pollctl`)
+4. `pthread_create`
+4. `pthread_self`
+4. `pthread_exit`
+4. `pthread_join`
+4. `pthread_kill`
+4. `pthread_detach`
+4. `pthread_sigmask`
+4. `getuid`
+4. `getgid`
+4. `geteuid`
+4. `getegid`
+4. `getgroups`
+4. `setuid`
+4. `setgid`
+4. `seteuid`
+4. `setegid`
+4. `setgroups`
+4. `chroot`
+4. `fchmodat`
+4. `fchownat`
+4. `faccessat`
+
+**LunaixOS**
 
 1. `yield`
 2. `geterrno`
 3. `realpathat`
 
-## 附录2：编译gcc作为交叉编译器<a id="appendix2"></a>
-
-注意，gcc需要从源码构建，并配置为交叉编译器，即目标平台为`i686-elf`。你可以使用本项目提供的[自动化脚本](slides/c0-workspace/gcc-build.sh)，这将会涵盖gcc和binutils源码的下载，配置和编译（没什么时间去打磨脚本，目前只知道在笔者的Ubuntu系统上可以运行）。
-
-**推荐**手动编译。以下编译步骤搬运自：https://wiki.osdev.org/GCC_Cross-Compiler 
-
-**首先安装构建依赖项：**
-```bash
-sudo apt update &&\
-     apt install -y \
-        build-essential \
-        bison\
-        flex\
-        libgmp3-dev\
-        libmpc-dev\
-        libmpfr-dev\
-        texinfo
-```
-
-**开始编译：**
-1. 获取[gcc](https://ftp.gnu.org/gnu/gcc/)和[binutils](https://ftp.gnu.org/gnu/binutils)源码
-2. 解压，并在同级目录为gcc和binutil新建专门的build文件夹
+( **※**：Indicate syscall is not tested )
 
-现在假设你的目录结构如下：
-```
-+ folder
-  + gcc-src
-  + binutils-src
-  + gcc-build
-  + binutils-build
-```
-
-3. 确定gcc和binutil安装的位置，并设置环境变量：`export PREFIX=<安装路径>` 然后设置PATH： `export PATH="$PREFIX/bin:$PATH"`
-4. 设置目标平台：`export TARGET=i686-elf`
-5. 进入`binutils-build`进行配置
-```bash
-../binutils-src/configure --target="$TARGET" --prefix="$PREFIX" \
-	--with-sysroot --disable-nls --disable-werror
-```
-然后 `make && make install`
-
-6. 确保上述的`binutils`已经正常安装：执行：`which i686-elf-as`，应该会给出一个位于你安装目录下的路径。
-6. 进入`gcc-build`进行配置
-```bash
-../gcc-src/configure --target="$TARGET" --prefix="$PREFIX" \
-	--disable-nls --enable-languages=c,c++ --without-headers
-```
-然后编译安装（取决性能，大约10~20分钟）：
-```bash
-make all-gcc &&\
- make all-target-libgcc &&\
- make install-gcc &&\
- make install-target-libgcc
-```
-8. 验证安装：执行`i686-elf-gcc -dumpmachine`，输出应该为：`i686-elf`
+## Appendix 2: Debugging with GDB remotely via UART
 
-**将新编译好的GCC永久添加到`PATH`环境变量**
+**(((( Broken after a refactoring years ago, need rework ))))**
 
-虽然这是一个常识性的操作，但考虑到许多人都会忽略这一个额外的步骤，在这里特此做出提示。
+The LunaixOS kernel comes with a built-in GDB debugging server, which runs on COM1@9600Bd. However, LunaixOS must be in debug mode before involving GDB.
 
-要想实现这一点，只需要在shell的配置文件的末尾添加：`export PATH="<上述的安装路径>/bin:$PATH"`。
+One could trigger the debug mode by writing a byte sequence `0x40` `0x63` `0x6D` `0x63`, to the same serial port. A text "DEBUG MODE" with magenta-coloured background shall be present at the bottom of the screen.
 
-这个配置文件是取决于你使用的shell，如zsh就是`${HOME}/.zshrc`，bash则是`${HOME}/.bashrc`；或者你嫌麻烦的，懒得区分，你也可以直接修改全局的`/etc/profile`文件，一劳永逸（但不推荐这样做）。
+Note that, whenever the text appears, the LunaixOS always halt all activities other than the debugging server, which means no scheduling and no external interrupt servicing. Users are now recommended to attach their GDB and drive the kernel with the debugging workflow.
 
-至于其他的情况，由于这个步骤其实在网上是随处可查的，所以就不在这里赘述了。
+Currently, LunaixOS implements the required minimal server-side command subset required by GDB Remote Protocol, namely, `g`, `G`, `p`, `P`, `Q`, `S`, `k`, `?`, `m`, `M`, `X`. Which should be enough to cover most debugging activities.
 
-## 附录3：Issue的提交<a id="appendix3"></a>
+When debugging is finished, one shall disconnect with `kill` command. This command will not force LunaixOS to power down the computer, instead it just resume the execution (identical behavior as `c` command). However, disconnecting does not means exiting of debug mode. The debug mode is still actived and any subsequent GDB attaching request shall remain the highest priority amongst all other activity. One shall deactivate the debug mode by writing byte sequence `0x40` `0x79` `0x61` `0x79` to the port, after GDB detached.
 
-由于目前LunaixOS没有一个完善强大的内核追踪功能。假若Lunaix的运行出现任何问题，还请按照以下的描述，在Issue里面提供详细的信息。
+### Limitations
 
-最好提供：
-+ 可用于复现问题的描述和指引（如Lunaix运行平台的软硬件配置）
-+ 错误症状描述
-+ （如可能）运行截图
-+ 错误消息（如果给出）
-+ 寄存器状态的dump
-+ （如可能）提供错误发生时，EIP附近的指令（精确到函数）。如果使用`make all-debug`，会提供`build/kdump.txt`，你可以在这里面定位。或者也可以直接`objdump`
-+ （如可能）虚拟内存映射信息（QEMU下可使用`info mem`查看）。
\ No newline at end of file
+Currently, one should avoid the use of `info stack`, `bt` or any other command that involves stack unwinding or stack backtracing. As it will somehow corrupt the stack layout and result in undefined behaviour. This issue should be addressed in future releases.