This is a toy kernel I wrote in order to learn about operating system implementation.

Demo

Specifications

• Preemptive Round-robin scheduler
• ATA hard disk driver
• FAT32 filesystem support
• Bitmap phycical memory allocator
• Runs ELF position independent executables
• Support for user mode and system calls

Build Prerequisites

A cross compiler , see https://wiki.osdev.org/GCC_Cross-Compiler.
Once the cross compiler is built, set the CC variable in makefile to the cross compiler path.

Build The kernel

cd /path/to/source/directory
make install

this should build and copy kernel.elf to the top directory

Run from command line

Install qemu emulator, and run:
qemu-system-x86_64 -machine pc -kernel kernel.elf [-hda hda.img]
where hda.img is a disk image file that the emulator will provide as a hard disk, see below

Debugging from command line

qemu-system-x86_64 -machine pc -kernel kernel.elf -s -S [-hda hda.img]
#on  another terminal :
gdb kernel.elf
set arch i386:x86-64
target remote localhost:1234 

Setting up the Project In eclipse

1. fix compiler errors

• project-->properties-->c/c++ build--> untick "generate makefile automatically ; and specify build location
• project-->properties-->c/c++ general--> pre-processor include paths-->providers tab-->check gcc cross builtin , and replace ${COMMAND} with the cross compiler command and ${FLAGS} with the correct flags ,see https://forum.osdev.org/viewtopic.php?f=13&t=29746

2. add run configuration:

• qemu : run-->external tools--> add qemu command
• qemu-debug: duplicate the qemu run configuration and add -s -S to arguments
• qemu--debug-connect :
  1. create a gdbinit file in the projects directory , and add "set arch i386:x86-64" to it
  2. debug-->debug configuration-->c/c++ remote application specify kernel.elf in program path
  3. at the bottom: click "select other"-->manual remote debugging launcher
  4. in debugger: select the gdbinit created for this project
  5. in debugger: connection tab --> specify the correct port qemu is listening to

3. add build configuration:

by default eclipse will run "make all" .
new build targets,ex: clean install, can be added with project-->build targets-->create

Making a partitioned image for testing

the following will make a disk image with dos partition table, and two FAT32 formatted partitions

dd if=/dev/zero of=hda.img bs=512 count=8064 
sudo losetup /dev/loop0 hda.img #may need "modprobe loop" before it
fdisk /dev/loop0
# do fdisk partitioning, pay attension to partition type : FAT32=0x0c
partprobe /dev/loop0 # to tell the kernel about partition table change, now /dev/loop0p1 and p2 should appear
mkdosfs -F32 -v /dev/loop0p1
mkdosfs -F32 -v /dev/loop0p2

or:

sudo losetup  -o 512  --sizelimit 2080256 /dev/loop1 hda.img  # 2080256 = 4063*512
mkdosfs -F32 -v /dev/loop1 #warning Not enough clusters for a 32 bit FAT! may be emmited
sudo losetup  -o 512  --sizelimit 2080768 /dev/loop2 hda.img  # 2080768 = 4064*512 
mkdosfs -F32 -v /dev/loop2

see https://wiki.osdev.org/Loopback_Device#Partitioning

to use the disk from host machine:

sudo losetup /dev/loop0 hda.img
partprobe /dev/loop0 
# now /dev/loop0p1  /dev/loop0p2 should apear, they can be mounted normally
# to detach device:
sudo losetup -d /dev/loop0 

Testing userspace apps

userspace programs can be built with the same cross compiler and linked against syscall wrappers for this os, like here.
an easy way to test the programs is to copy them to the disk image as above, and from the terminal issue "exec drvn/path/to/executable"

Making an iso

intall xorriso, mtools, grub-mkrescue
./makeiso.sh