lab 1 finished
GNUMakefile changed
Merge branch 'lab1' into lab2

Conflicts:
	GNUmakefile
Exercise 4 is done
lab 2 finished
KERNBASE using 4MB page
disable 4MB size page
memchmod is added
lab3
lab3 exercise 2
save but still have bugs
lab2 exercise2 completed
trap
lab3 completed
breakpoint
fast system call
enter lab4