CS 570 OPERATING SYSTEMS
M
ARIE ROCH
Assignment 1
Part I must be done individually. Part II may be done with a pair programmer if desired.
As with all assignments in this class, qualitative questions should be answered with
grammatically correct sentences.
Due, Monday, Feb 18th at the beginning of class.
Part I – Questions, 20 points each
1. Describe in your own words the process that occurs when a privileged
instruction is executed in the kernel code of a virtual machine with a type I
hypervisor.
2. You are writing user library code for a new operating system, MejorOS for a
MIPS RISC processor. MIPS chips use the instruction syscall in place of
TRAP, but the functionality is the same as a TRAP instruction. You are to
write subroutine int print_string(char *str) which writes a NULL terminated
string (pointed to by str) to the current output device. If successful, the
subroutine should return 0, otherwise 1. You need not do any error checking,
as this will have been done by higher level library routines such as printf
which call print_string.
The kernel programming interface for MejorOS states that to print a string to
the current output device, the value 0x90 should be loaded into register v0
and the address of the string in register r4. Upon returning from the
exception, register r0 contains the result of the system code (0 if successful, 1
otherwise). In addition to syscall, you will need to use the following
instructions:
• immediate load: li destination_register, value which
loads the given value (immediate data) into the specified register.
• load word: lw destination_register, address, which loads
the contents of address into destination_register.
• store word: sw source_register, address, which saves
source_register to the specified address.
Fortunately, you are using a C/C++ compiler which has an extension for
including assembler instructions. Any block preceded by __asm contains
assembly instructions and if the compiler can translate C/C++ variables into
addresses. As an example, if the variable foo was declared as a word sized
integer, one could write a function void bar(int foo) as follows:
