A basic x86_64 bit kernel implementation.

Things Implemented:

1. Preemptive OS (scheduling of processes on timer interrupt)
2. Virtual Memeory Manager 
3. Paging 4KB pages
4. Process management (process creation, VMA)
5. fork
6. Yield()
7. Execve()
8. Copy on write handling on fork
9. User Stack with limit of 32kb
10. SEGV handling
11. Tarfs handling
12. stdin, stdout, stderr
13. read(), write()
14. Binaries: ps, shell
15. Libc:
	a. User space malloc with local handling(makes syscall only when not enough memory locally)
	b. fork user space
	c. execve() execvep **NOT IMPLEMENTED**
	d. wait, waitpid, exit, getpid
	e. open, close, read, opendir, closedir, readdir
	f. printf, scanf


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qemu-system-x86_64 -curses -cdrom $USER.iso -drive id=disk,file=$USER.img,if=none -device ahci,id=ahci -device ide-drive,drive=disk,bus=ahci.0 -gdb tcp::NNNN




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How to test:

1. There is a hello binary in /bin/hello which demonstrates fork from shell --> execve() to hello --> fork in hello --> then PREMPTIVE scheduling between CHILD & PARENT of hello.
   - The hello binary prints continious "PARENT" in a while loop when in PARENT process and prints continious "CHILD" in while loop when in child.

TO USE hello:
	Type bin/hello in shell prompt it will start printing PARENT in while loop till the next timer interript after then it will start printing CHILD in a while loop


2. The timer tic frequency can be adjusted in /sys/irq.c in timer handler function which starts ar line no:173
3. Kernel Paging/Self Refrencing is implemented in /sys/kern_pagetable.c
4. Physical memory managements(creation of free list etc.) are implemented in pmem_manager.c 
5. Keyboard, timer handler are implemented in /sys/irq.c
6. Page fault, GPF, SEGV, INT 50 system call handler are implemnted in /sys/isr.c
7. The execve is implemented in /sys/execve.c
8. exit(), wait, waitpid, ps are implemented in /sys/process_que.c
8. Virtual memory management is implementes in /sys/v_mem_manager.c
9. Process Management is implemented in /sys/task_managemnt.c
10. Scheduler is implemented in /sys/task_switch.c
11. libc header files are in /include/libc
12. libc system call wrappers are implemented in libc folder


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