# Homework: xv6 and Interrupts and Exceptions

Read: xv6's trapasm.S, trap.c, syscall.c, vectors.S, and usys.S. Skim lapic.c, ioapic.c, and picirq.c

Hand-In Procedure

You are to turn in this homework during lecture. Please write up your answers to the exercises below and hand them in to a 6.828 staff member at the beginning of the lecture.

Introduction

Try to understand xv6's trapasm.S, trap.c, syscall.c, vectors.S, and usys.S. Skim You will need to consult:

Chapter 5 of IA-32 Intel Architecture Software Developer's Manual, Volume 3: System programming guide; you can skip sections 5.7.1, 5.8.2, and 5.12.2. Be aware that terms such as exceptions, traps, interrupts, faults and aborts have no standard meaning.

Chapter 9 of the 1987 i386 Programmer's Reference Manual also covers exception and interrupt handling in IA32 processors.

Assignment: In xv6, set a breakpoint at the beginning of `syscall()` to catch the very first system call. What values are on the stack at this point? Turn in the output of `print-stack 35` at that breakpoint with each value labeled as to what it is (e.g., saved `%ebp` for `trap`, `trapframe.eip`, etc.).

This completes the homework.