R(os) mini project

this is my toy os project made just for fun and learning purposes

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< how to build >

make # (or make -B)
make run

how to build gcc cross compiler

---

first we need to know 1(what is a cross compiler) and 2(why we need such a thing):

1 - A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is running.

2 - It is possible ask your compiler what target platform it is currently using by calling the command:

 gcc -dumpmachine

If you are developing on 64-bit Linux, then you will get a response such as x86_64-unknown-linux-gnu. This means that the compiler thinks it is creating code for Linux. If you use this GCC to build your kernel, it will use your system libraries, headers, the Linux libgcc, and it will make a lot of problematic Linux assumptions. If you use a cross-compiler such as i686-elf-gcc, then you get a response back such as i686-elf that means the compiler knows it is doing something else and you can avoid a lot of problems easily and properly.

how to make a gcc cross compiler (well it's hard)

first we intall dependencies:

sudo apt install build-essential bison flex libgmp3-dev libmpc-dev libmpfr-dev texinfo libisl-dev

make a directory for binaries:

mkdir cross/

and a directory for sources we download:

mkdir src/

and two directories for builds:

mkdir binutils-build gcc-build

cd to sources folder to download the source files:

cd src/

then we download binutils and gcc source (from official gnu mirrors WEBSITE):

http://ftp.gnu.org/gnu/binutils/binutils-x.y.z.tar.gz

tar xf binutils-x.y.z.tar.gz

https://ftp.gnu.org/gnu/gcc/gcc-10.2.0/gcc-x.y.z.tar.gz

tar xf gcc-x.y.z.tar.gz

directory tree looks like this:

• src/
  gcc-build/
  binutils-build/
  

build(GCC):

cd gcc-build
../gcc-12.2.0/contrib/download_prerequisites

../gcc-12.2.0/configure --target="i686-elf" --prefix="$HOME/cross" --disable-nls --enable-languages=c,c++ --without-headers
make all-gcc
make all-target-libgcc
make install-gcc
make install-target-libgcc

build(BINUTILS):

../binutils-2.39/configure --target="i686-elf" --prefix="$HOME/cross" --with-sysroot --disable-nls --disable-werror
cd binutils-build
make 
make install

done -_-

now you should have your cross compiler and linker inside cross/bin :)

How Linker Scripts Work!!!

---

SECTIONS
{

    . = 0x10000;

    .text : { *(.text) }

    . = 0x8000000;

    .data : { *(.data) }

    .bss : { *(.bss) }

}

You write the SECTIONS command as the keyword SECTIONS, followed by a series of symbol assignments and output section descriptions enclosed in curly braces. The first line in the above example sets the special symbol ., which is the location counter. If you do not specify the address of an output section in some other way (other ways are described later), the address is set from the current value of the location counter. The location counter is then incremented by the size of the output section. The second line defines an output section, .text. The colon is required syntax, which may be ignored for now. Within the curly braces after the output section name, you list the names of the input sections, which should be placed into this output section. The * is a wildcard which matches any file name. The expression *(.text) means all .text input sections in all input files. Since the location counter is 0x10000 when the output section .text is defined, the linker will set the address of the .text section in the output file to be 0x10000. The remaining lines define the .data and .bss sections in the output file. The .data output section will be at address 0x8000000. When the .bss output section is defined, the value of the location counter will be 0x8000000 plus the size of the .data output section. The effect is that the .bss output section will follow immediately after the .data output section in memory. That's it! That's a simple and complete linker script. (source)

useful links

---

[ CS crash course youtube ]

https://youtube.com/playlist?list=PL8dPuuaLjXtNlUrzyH5r6jN9ulIgZBpdo

[operating system videos]

https://youtu.be/9GDX-IyZ_C8
https://www.youtube.com/playlist?list=PLEJxKK7AcSEGPOCFtQTJhOElU44J_JAun
https://www.youtube.com/playlist?list=PLBlnK6fEyqRiVhbXDGLXDk_OQAeuVcp2O

[ how cpu works (very good videos should be watched multiple times!) ]
|fetch-decode-execute cycle|

https://youtu.be/cNN_tTXABUA
https://youtu.be/Z5JC9Ve1sfI

Refrence website ==> https://wiki.osdev.org

[ os dev playlists ]
1 - https://www.youtube.com/playlist?list=PLm3B56ql_akNcvH8vvJRYOc7TbYhRs19M ( Daedalus Community )
2 - https://www.youtube.com/playlist?list=PLFjM7v6KGMpiH2G-kT781ByCNC_0pKpPN ( nanobyte )
3 - https://www.youtube.com/playlist?list=PLHh55M_Kq4OApWScZyPl5HhgsTJS9MZ6M ( Write your own Operating System )

why protected mode => https://stackoverflow.com/questions/48743371/why-do-we-need-to-enter-32-bit-protected-mode-anyway

[ good channels ]

• https://www.youtube.com/channel/UCKS34cSMNaXaySe2xgXH-3A
• https://www.youtube.com/watch?v=Z5JC9Ve1sfI