Introduction

Overview Administrivia More Languages! Setup Student Voice

Reference

Visual Studio Code VSC Cloning replit.com Git Gitlab Setup Using GitLab VSC GitLab Terminal;GitLab

1. Basic Operations

Basic Operations Binary Recap Basic Operations Floating Point Numbers Basic Operations - Summary Basic Operations - Task Sheet 1 Basic Operations - Task Sheet 2

2. Memory

Memory The Stack Methods & Frames Stack Step By Step Recursion Primitives Vs Objects I The Heap Primitives Vs Objects II Frame Detail Summary Java Memory Exercise

3. C Programming

The C Programming Language C Basics C Variables C Branching & Loops C Operators C Functions C Strings C Input/Output C Code Organisation C Programming - Task Sheet

4. C Memory

C Memory C Pointers C Arrays C Lab Session 2

5. C Struct

C Data Structures C Struct Pointer Guide

C Linked Lists Exercises 1 External Pages Pointers To Pointers Doubly Linked Lists Doubly Linked Lists Node Based Stacks Stacks - Node Based Exercises 2 Trees Binary Trees Binary Search Trees Exercises 2

7. Assembly Language

Assembly PC Hardware Assembly Environment Setup Assembly Basics Registers System Calls Variables & Constants Arithmetic Logic Conditions Loops Exercises Numbers Procedures & The Stack Debugging Assembly Generating Assembly From C

Debugging Assembly

Debugging Preparation

To debug our assembly code we need to compile and link it slightly differently. To compile main.asm use the following commands.

nasm -f elf -g -o main.o main.asm
ld -m elf_i386 -o main main.o

In the setup we’ve been using to compile and run our programs, you can change main.sh to the following

nasm -f elf -g -o main.o main.asm ld -m elf_i386 -o main main.o ./main

For reference we’ve added the -g flag to the nasm line and removed the -s flag from the ld line.

These changes generate debugging information that can be used by gdb.

Using gdb

After we have compiled and linked our assembly code we can use gdb from the terminal window.

gdb main will launch the debugger.

The prompt will change to (gdb)

gdb defaults to a different syntax to the one we are using. To change to Intel syntax enter

set disassembly-flavor intel

You will need to do this each time you start gdb.

gdb has the following commands

break x creates a breakpoint at the label x
break x+y creates a breakpoint y bytes after the label x
run starts the code running. it will stop at the first breakpoint
continue will restart the code running if it has stopped at a breakpoint
stepi or si will run the next instruction, stepping in to any functions
nexti or ni will run the next instruction but not step in to functions

To start debugging at the start of your code use the commands

break _start
run

You can use the commands above to step through the code.

Layout

To aid in debugging we can use the layout command within gdb so that we can see the contents of the registers and the assembly code.

To set layout up, compile and link your code and run gdb as follows -

gdb main
(gdb) set disassembly-flavor intel
(gdb) break _start
(gdb) run
(gdb) layout asm
(gdb) layout regs

You should see something like this -

gdb layout

The upper section of the layout shows the registers and their contents.
The middle section of the layout shows the code with the current line highlighted.
You can enter the gdb commands in the bottom section of the layout.

As you step through the code you will see the registers updated.

Improve this page