Embedded-Hacking/WEEK02/WEEK02-03-S.md

Embedded Systems Reverse Engineering

Repository

Week 2

Hello, World - Debugging and Hacking Basics: Debugging and Hacking a Basic Program for the Pico 2

Non-Credit Practice Exercise 3 Solution: Examine Memory Around Your String

Answers

GDB Commands

(gdb) set {char[14]} 0x20000000 = {'h','a','c','k','y',',',' ','w','o','r','l','d','\r','\0'}
(gdb) x/20b 0x20000000

Byte Dump Output

0x20000000: 0x68 0x61 0x63 0x6b 0x79 0x2c 0x20 0x77
0x20000008: 0x6f 0x72 0x6c 0x64 0x0d 0x00 0x00 0x00
0x20000010: 0x00 0x00 0x00 0x00

ASCII Mapping

Offset	Hex Value	Character
0x00	0x68	h
0x01	0x61	a
0x02	0x63	c
0x03	0x6b	k
0x04	0x79	y
0x05	0x2c	, (comma)
0x06	0x20	(space)
0x07	0x77	w
0x08	0x6f	o
0x09	0x72	r
0x0a	0x6c	l
0x0b	0x64	d
0x0c	0x0d	\r (carriage return)
0x0d	0x00	\0 (null terminator)

Reflection Answers

1. Which bytes mark the end of the printable string, and why are they needed? The last two meaningful bytes are 0x0d (carriage return \r) and 0x00 (null terminator \0). The null terminator signals the end of the string to puts(). Without it, puts() would read past the intended string and print garbage memory until a null byte is encountered.

2. How would misaligned writes show up in the byte view? If you write to an incorrect address or use wrong character offsets, the byte dump would show unexpected values at wrong positions. Characters would appear shifted, and adjacent data structures could be corrupted.

3. What risks arise if you overwrite bytes immediately after your string? Overwriting adjacent bytes could corrupt other data structures in SRAM, such as variables, linked lists, or runtime metadata. This could cause unpredictable crashes or silent data corruption depending on what occupies those memory locations.