I started this project, because I wanted to learn how to write a kernel. Quickly, I found out how way in over my head I was when it comes to C, Make, and Linux. Therefore, I went to Google & started looking for resources. From the get-go I knew there wouldn't be a simple "100 steps to your own Kernel", thus, I focused on searching for specific keywords. Such as "kernel", "kernel development", "kernel programming", "kernel programming tutorial", "kernel programming guide", "libc kernel", "memory management", "memory management tutorial", "memory management guide" & more. Eventually I came across Wikipedia, OSDev & Kernel.org.
Obviously I didn't just copy and paste code from the tutorials / resources above & call it my own Kernel. I did however, put effort into learning exactly why things are done (such as the purpose of linker.ld & boot.asm). Furthermore, I use JetBrains tool suite to write my code, under their student licence. Specifically I useCLion for C++ while it mas MakeFile support. It is not as clean as the Cmake support. Thus, I wrote CMakeLists.txt script in order to have my entire kernel be able to be compiled with CMake.
One of the first bugs I encountered was that CMake complained that my Cross-Compiler was failing its tests, due to the default "dynamic" parameter that is used, thus I found through much trail & error along with "Google-Fu", that we can actually set CMake parameters such that it looks like all compiler tests will pass. The 5 lines of code below are these parameters:
set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_CROSSCOMPILING 1)
set(CMAKE_CXX_COMPILER_WORKS TRUE)
set(CMAKE_C_COMPILER_WORKS TRUE)
set(CMAKE_ASM_COMPILER_WORKS TRUE)For the first 1 or 2 days of attempting to get this working, I was using add_library() for my kernel. However, I found
that I should instead be using add_executable() & target_link_libraries() in order to get the linker to work.
I added a debug message to list all sources that "GLOB RECURSE" found. This is to help me debug any issues I may encounter in the future.
While looking through Meaty Skeleton, structure, I found that they put a lot of the "terminal" printing characters code in this file & it caused me to look deeper into the meaning behind this acronym. "TTY" stands "teletypewriter", which is refering to (funny enough) Unix terminal. The phrase coming from the "old days". This StackOverflow answer was especially useful. In this definition.
I extended the ability of this TTY.c to support terminal_moveup(), which essentially removes the first line of the terminal,
and moves all the lines up, giving the affect of scrolling. This is achieved by changing the VGA array.
As previously mentioned I use CLion for C++. Configuring CLion to properly work was a bit of a challenge. The following image contains the configuration setup:
Where "CMake Application" defines the configurations' auto-detected by CLion.
Remote Debug, was the GDB configuration needed to debug my kernel through QEMU.
& Start QEMU shell script started the QEMU emulator with necessary parameters & arguments.