An overview of the Portable Executable (PE) File Structure

Introduction

Portable Executable (PE) files are the standard file format for executables and dynamic-link libraries (DLLs) in the Windows operating system. In this article, we will discuss the structure of PE files and how it is used by the Windows operating system to execute and load applications.

What is a PE File?

A Portable Executable (PE) file is a binary file format used by Microsoft Windows operating systems. PE files contain executable code, resources, and metadata required to run an application or library in Windows. Some of the common file extensions for PE files include .exe, .dll, .sys, and .ocx.

PE File Structure

The PE file structure is divided into several sections, each with its own specific purpose. These sections contain different types of data that the operating system uses to execute and load applications. Some of the most important sections include:

1. DOS header - This section contains information about the file format, such as the location of the PE header and the size of the file.

2. PE header - This section contains information about the target architecture, the number of sections, and the size of optional header data.

3. Optional header - This section contains information about the entry point, the stack size, and the size of image data.

4. Data directories - This section contains pointers to important data structures, such as the import table, the export table, and the resource table.

5. Section headers - This section contains information about the data in each section, such as the size of the section, the location of the data, and the access permissions.

6. Section data - This section contains the actual data of the PE file, such as code, resources, and metadata.

How PE Files are Used by Windows

When a PE file is executed in Windows, the operating system uses the information contained in the PE header and data directories to load the application into memory and execute it. The following steps summarize the process:

1. The operating system reads the DOS header to determine the location of the PE header.

2. The operating system reads the PE header to determine the number of sections, the size of the optional header, and the location of the data directories.

3. The operating system reads the optional header to determine the entry point of the application, the size of the image data, and the size of the stack.

4. The operating system reads the data directories to locate the import table, export table, and resource table.

5. The operating system loads the section data into memory and relocates the image if necessary.

6. The operating system sets up the stack and the entry point of the application, and then executes the code.

Examples of PE Files

Here are a few examples of commonly encountered PE files:

1. .exe files - These are executable files that are run by the operating system to launch applications.

2. .dll files - These are dynamic-link libraries that are loaded by applications to provide additional functionality.

3. .sys files - These are system files that are used by the operating system to provide device drivers and other low-level functionality.

4. .ocx files - These are ActiveX control files that are used by applications to provide additional functionality and interact with other applications.

Conclusion

The Portable Executable (PE) file format is an integral part of the Windows operating and is used to execute and load applications and libraries. Understanding the structure of PE files and how they are used by Windows is important for developers and security professionals who work with Windows-based systems. The PE file format has evolved over time to support new features and improvements, but the basic structure has remained largely unchanged for many years, making it a stable and well-understood part of the Windows ecosystem.