Programmers: Nate Sullivan (sullivan) and Ryan Schmukler (schmukle)
Project 3



Memory Allocation--

Made a linked list of free nodes to keep track of unallocated memory. 

For initialization, we created one large node using mmap. 

For subsequent memory allocation, we searched the linked list for the largest chunk of unallocated memory and allocated the requested amount from the beginning of that chunk, plus a header to keep track of the size. We then updated the list to reflect the allocation. 

For memory freeing, we looked to the header for the size of the chunk to be freed. We created a node for that chunk and then coalesced with adjacent nodes as appropriate.


xv6 Null Pointer--

Changed exec to leave the zeroth page of memory zeroed out. Loaded program code at page one. 

Changed syscall.c to throw an error for null pointers being requested from the kernel. 

Changed vm.c to have copyuvm copy 1 page beyond the start of a process' page table so as to not have multiple pages of 0s.

Changed Makefile to tell user programs to start execution at page one rather than page zero.