Student: Trevor Blanchard
Course: Comp 4430 OS2
Date: March 14, 2016
Lab 4 Memory Management 

Part 1

loop over all the pdes (1024)
proc.c line 465 *pde = &(p->pgdir[j]);

get the page table from the PPN
proc.c line 468 pgtab = (pte_t*)p2v(PTE_ADDR(*pde));

loop over all the ptes (1024)
proc.c line 471 pte = &pgtab[k];

read the address from the PPN
proc.c line 473 va = (uint*)p2v(PTE_ADDR(*pte));

Part 2

Don't allow The first page to be addressed
exec.c line 19 sz = PGSIZE - 1;

skip the first page when walking
vm.c line 317 for(i = PGSIZE; i < sz; += PGSIZE){

Make the text data start at address 0x1000 for xv6 and _forktest
README line 140 $(LD) $(LDFLAGS) -N -e main -Ttext 0x1000 -o $@ $^
README line 147 $(LD) $(LDFLAGS) -N -e main -Ttext 0x1000 -o _forktest forktest.o ulib.o usys.o

Part 3

Added another parameter to allocuvm - int perm -
exec is now responsible for passing PTE_W|PTE_U or PTE_U
exec checks the program section for the writable bit and passes it to allocuvm
updated all other references to allocuvm
added -no-omagic to makefile instead of -N for page alignment