Lesson 2

Question 1

trap instruction

Answer 1

Sets kernel mode,integrated with the system call in C code

Question 2

Calling kernel level from user level

Answer 2

system call interface

Question 3

Handles inter-process communication, scheduling and memory management

Answer 3

Process Control System

Question 4

Handles hardware from kernel level

Answer 4

Hardware Control

Question 5

System call with TWO return values

Answer 5

parent gets PID of child, child gets 0

Question 6

The stacks of a Unix process

Answer 6

One for user mode

One for system calls in kernel mode

Question 7

Memory layout: Text

Answer 7

read-only machine code

Question 8

4 facts after a fork

Answer 8

• Child gets a copy of parent’s code and data
• except fork returns child’s PID to parent, and zero to child
• Parent and child share the same open files
• Child gets copy of parent’s signal table, but with no pending signals

Question 9

wait [n]

Answer 9

• pauses until execution of a background process with PID = n has ended
• If n not given, waits for all processes known to it
• returns the exit status of the last job which terminated
• returns 127 in the event that n specifies a non-existent job
• returns zero if no jobs to wait for

Question 10

exec

Answer 10

Change program in the current process, keeping the old PID

Question 11

critical resource

Answer 11

to be deterministic: only one process or thread at a time

Question 12

static - on variables declared outside function (and functions themselves)

Answer 12

not visible outside the declaring file

Question 13

static - on variables declared inside functions

Answer 13

keeping value from one function execution to the next.