Memory Sections in C

Introduction

While high-level languages like Python and Java often abstract memory management details, in C and C++, understanding the layout of memory sections is crucial.

The Anatomy of Program Memory

When a program is executed, the operating system loads it into memory, segmenting it into several sections:

Text Segment

This is the section where the compiled machine code of the program resides.

It’s generally marked as read-only to prevent the program from accidentally modifying its own instructions.

Understanding this segment is particularly crucial for activities like reverse engineering and exploit development.

Data Segment

Initialized Data Segment

Stores global and static variables that have an initial value. For instance, int i = 10; would be stored here.

Uninitialized Data Segment (BSS)

Stands for “Block Started by Symbol.” This section contains uninitialized global and static variables, usually initialized to zero by default.

Stack

The stack is used for function call management. It stores local variables, function parameters, return addresses, and performs process execution control. Each thread in a program has its own stack. In hacking, stack overflows are a commonly exploited vulnerability.

Heap

The heap is used for dynamic memory allocation where variables are allocated and freed at runtime. Functions like malloc() and free() in C or new and delete in C++ manipulate data in the heap.

Practical Implications

Immutable String Literals

When you declare a string literal in C, it’s usually placed in the text segment, which is read-only. Attempting to modify it can result in a segmentation fault.

Buffer Overflows

Understanding the stack’s behavior can help in both exploiting and preventing buffer overflows attacks.

Memory Leaks

Poor heap management can result in memory leaks, making your program or even the entire system unstable.

A Brief Look at Memory Sections in Other Languages

• Python: Python abstracts much of memory management, but understanding the CPython implementation can be beneficial.
• Java: In Java, the Java Virtual Machine (JVM) handles memory, but concepts like garbage collection can be understood better with a foundational knowledge of memory sections.