Enrico Fraccaroli
330 lines
9.1 KiB
Markdown
330 lines
9.1 KiB
Markdown
# MentOS
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[](https://forthebadge.com)
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[](https://forthebadge.com)
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[](https://forthebadge.com)
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## 1. What is MentOS
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MentOS (Mentoring Operating System) is an open source educational operating
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system. The goal of MentOS is to provide a project environment that is realistic
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enough to show how a real Operating System work, yet simple enough that students
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can understand and modify it in significant ways.
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There are so many operating systems, why did we write MentOS? It is true, there
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are a lot of education operating system, BUT how many of them follow the
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guideline de fined by Linux?
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MentOS aims to have the same Linux's data structures and algorithms. It has a
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well-documented source code, and you can compile it on your laptop in a few
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seconds!
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If you are a beginner in Operating-System developing, perhaps MentOS is the
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right operating system to start with.
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Parts of MentOS are inherited or inspired by a similar educational operating
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system called [DreamOs](https://github.com/dreamos82/DreamOs) written by Ivan
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Gualandri.
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## 2. Implemented features
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Follows the list of implemented features:
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**Processes and Events**
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- [x] Memory protection (User vs Kernel);
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- [x] Processes;
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- [x] Scheduler (synchronous and asynchronous);
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- [x] Interrupts and Exceptions;
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- [x] Signals;
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- [x] Timers and RTC;
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- [x] Wait-queues;
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- [x] System Calls;
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- [ ] Multi-core;
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**Memory**
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- [x] Paging;
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- [x] Buddy System;
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- [x] Slab Allocation;
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- [x] Zone Allocator;
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- [x] Cache Allocator;
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- [x] Heap;
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- [x] Virtual Addressing;
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**Filesystem**
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- [x] Virtual Filesystem (VFS);
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- [x] Initramfs;
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- [x] EXT2;
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- [x] Procfs;
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**Input/Output**
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- [x] Programmable Interrupt Controller (PIC) drivers;
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- [x] Keyboard drivers (IT/ENG layouts);
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- [x] Video drivers;
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- [ ] VGA drivers;
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I will try to keep it updated...
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## 3. Prerequisites
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MentOS is compatible with the main **unix-based** operating systems. It has been
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tested with *Ubuntu*, *WSL1*, *WSL2*, and *MacOS*.
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### 3.1. Generic Prerequisites
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#### 3.1.1. Compile
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For compiling the system:
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- nasm
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- gcc
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- make
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- cmake
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- git
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- ccmake (suggested)
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- e2fsprogs (should be already installed)
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Under **MacOS**, for compiling, you have additional dependencies:
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- i386-elf-binutils
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- i386-elf-gcc
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#### 3.1.2. Execute
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To execute the operating system, you need to install:
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- qemu-system-i386 (or qemu-system-x86)
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#### 3.1.3. Debug
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For debugging we suggest using:
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- gdb or cgdb
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### 3.2. installation Prerequisites
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Under **Ubuntu**, you can type the following commands:
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```bash
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sudo apt-get update && sudo apt-get upgrade -y
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sudo apt-get install -y build-essential git cmake qemu-system-x86 nasm e2fsprogs
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sudo apt-get install -y gdb cgdb
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```
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Note: Older versions might have `qemu-system-i386` instead of `qemu-system-x86`.
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Under **MacOS** you also need to install the i386-elf cross-compiler. The
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simplest installation method is through Homebrew package manager.
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Install [Homebrew](https://brew.sh/index_it) if you don't already have it, and
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then type the following commands:
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```bash
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brew update && brew upgrade
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brew install i386-elf-binutils i386-elf-gcc git cmake qemu nasm e2fsprogs
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brew install gdb cgdb #<- for debug only
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```
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## 4. Compiling MentOS and generating the EXT2 filesystem
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Compile MentOS with:
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```bash
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cd <clone_directory>
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mkdir build
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cd build
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cmake ..
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make
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```
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Then, generate the EXT2 filesystem with:
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```bash
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make filesystem
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```
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you just need to generate the filesystem once. If you change a `program` you need to re-generate the entire filesystem with `make filesystem`, but this will override any changes you made to the files inside the `rootfs.img`. In the future I will find a way to update just the `/usr/bin` directory and the programs.
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## 5. Running MentOS
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Boot MentOS with qemu:
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```bash
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make qemu
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```
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To login, use one of the usernames listed in `files/etc/passwd`.
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## 6. Kernel logging
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The kernel provides ways of printing logging messages *from* inside the kernel code *to* the bash where you executed the `make qemu`.
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These *logging* functions are:
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```C++
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#define pr_emerg(...)
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#define pr_alert(...)
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#define pr_crit(...)
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#define pr_err(...)
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#define pr_warning(...)
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#define pr_notice(...)
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#define pr_info(...)
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#define pr_debug(...)
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#define pr_default(...)
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```
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You use them like you would use a `printf`:
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```C++
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if (fd < 0) {
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pr_err("Failed to open file '%s', received file descriptor %d.\n", filename, fd);
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return 1;
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}
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```
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By default only message that goes from `pr_notice` included down to `pr_emerg` are displayed.
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Each logging function (they are actually macros) is a wrapper that automatically sets the desired **log level**. Each log level is identified by a number, and declared as follows:
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```C++
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#define LOGLEVEL_DEFAULT (-1) ///< default-level messages.
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#define LOGLEVEL_EMERG 0 ///< system is unusable.
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#define LOGLEVEL_ALERT 1 ///< action must be taken immediately.
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#define LOGLEVEL_CRIT 2 ///< critical conditions.
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#define LOGLEVEL_ERR 3 ///< error conditions.
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#define LOGLEVEL_WARNING 4 ///< warning conditions.
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#define LOGLEVEL_NOTICE 5 ///< normal but significant condition.
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#define LOGLEVEL_INFO 6 ///< informational.
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#define LOGLEVEL_DEBUG 7 ///< debug-level messages.
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```
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You can change the logging level by including the following lines at the beginning of your source code:
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```C++
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// Include the kernel log levels.
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#include "sys/kernel_levels.h"
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/// Change the header.
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#define __DEBUG_HEADER__ "[ATA ]"
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/// Set the log level.
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#define __DEBUG_LEVEL__ LOGLEVEL_INFO
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```
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This example sets the `__DEBUG_LEVEL__`, so that all the messages from `INFO` and below are shown. While `__DEBUG_HEADER__` is just a string that is automatically prepended to your message, helping you identifying from which code the message is coming from.
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## 7. Change the scheduling algorithm
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MentOS provides three different scheduling algorithms:
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- Round-Robin
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- Priority
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- Completely Fair Scheduling
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If you want to change the scheduling algorithm:
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```bash
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cd build
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# Round Robin scheduling algorithm
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cmake -DSCHEDULER_TYPE=SCHEDULER_RR ..
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# Priority scheduling algorithm
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cmake -DSCHEDULER_TYPE=SCHEDULER_PRIORITY ..
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# Completely Fair Scheduling algorithm
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cmake -DSCHEDULER_TYPE=SCHEDULER_CFS ..
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make
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make qemu
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```
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Otherwise you can use `ccmake`:
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```bash
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cd build
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cmake ..
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ccmake ..
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```
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Now you should see something like this:
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```
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BUILD_DOCUMENTATION ON
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CMAKE_BUILD_TYPE
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CMAKE_INSTALL_PREFIX /usr/local
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DEBUGGING_TYPE DEBUG_STDIO
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ENABLE_BUDDY_SYSTEM OFF
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SCHEDULER_TYPE SCHEDULER_RR
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```
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Select SCHEDULER_TYPE, and type Enter to scroll the three available algorithms
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(SCHEDULER_RR, SCHEDULER_PRIORITY, SCHEDULER_CFS). Afterwards,
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```bash
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<press c>
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<press g>
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make
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make qemu
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```
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## 8. Use Debugger
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If you want to use GDB to debug MentOS, first you need to compile everything:
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```bash
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cd build
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cmake ..
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make
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```
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Then, you need to generate a file called `.gdbinit` placed inside the `build` directory, which will tell **gdb** which *object* file he needs to read in order to allow proper debugging. To generate the file, just execute:
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```bash
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make gdbinit
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```
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Finally, you run qemu in debugging mode with:
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```bash
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make qemu-gdb
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```
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If you did everything correctly, you should see an empty QEMU window. Basically, QEMU is waiting for you to connect *remotely* with gdb. Anyway, running `make qemu-gdb` will make your current shell busy, you cannot call `gdb` in it. You need to open a new shell inside the `build` folder and do a:
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```bash
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cgdb -q -iex 'add-auto-load-safe-path .'
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```
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Now you will have:
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1. the QEMU window waiting for you,
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2. the shell where you ran `make qemu-gdb` also waiting for you,
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3. the debugger that loaded a series of symbol files and the location of their `.text` section.
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By default I placed a breakpoint at the begginning of 1) the bootloader, 2) the `kmain` function of the kernel.
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So, when gdb starts you need to first give a continue:
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```bash
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(gdb) continue
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```
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This will make the kernel run, and stop at the first breakpoint which is inside the *bootloader*:
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```bash
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Breakpoint 1, boot_main (...) at .../mentos/src/boot.c:220
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220 {
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```
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giving a second `continue` will get you to the start of the operating system:
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This will make the kernel run, and stop at the first breakpoint which is inside the *bootloader*:
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```bash
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Breakpoint 2, kmain (...) at .../mentos/src/kernel.c:95
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95 {
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```
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## 9. Contributors
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Project Manager:
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* [Enrico Fraccaroli](https://github.com/Galfurian)
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Developers:
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* [Alessandro Danese](https://github.com/alessandroDanese88), [Luigi Capogrosso](https://github.com/luigicapogrosso), [Mirco De Marchi](https://github.com/mircodemarchi)
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- Protection ring
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- libc
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* Andrea Cracco
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- Buddy System, Heap, Paging, Slab, Caching, Zone
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- Process Image, ELF
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- VFS: procfs
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- Bootloader
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* Linda Sacchetto, Marco Berti
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- Real time scheduler
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* Daniele Nicoletti, Filippo Ziche
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- Real time scheduler (Asynchronous EDF)
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- Soft IRQs
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- Timer
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- Signals
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