Executable

Description

An executable is a file or binary that contains a compiled program capable of being executed by a computer’s operating system without needing further compilation or interpretation. It typically includes machine code, metadata, and sometimes embedded resources (like icons or configuration data).

Executables are the final product of the build process, transforming human-readable source code into a low-level format that the computer can run directly. These files often have specific extensions (like .exe on Windows or no extension on Unix-like systems) and are tailored for a particular processor architecture and operating system.

Key Characteristics

Common Executable File Extensions

Note: Files like .jar or .py need an interpreter/runtime and are not true native executables.

How Executables Are Created

1. Source Code → Written in high-level languages (C, C++, Rust, etc.)
2. Compilation → Translates source into machine code using a compiler.
3. Linking → Resolves references to libraries, system calls, and other components.
4. Packaging → Combines code and metadata into an executable file.

Example in C:

// hello.c
#include <stdio.h>
int main() {
    printf("Hello, world!\n");
    return 0;
}

Compile and create executable:

gcc hello.c -o hello
./hello

File Structure of an Executable

For Windows (PE format):

• DOS Header
• PE Header
• Text Section (.text) – Contains compiled code
• Data Section (.data) – Static variables
• Import Table – References to external DLLs
• Export Table – Functions exposed to other binaries

For Linux (ELF format):

• ELF Header
• Program Header Table
• Section Headers
• Code and Data Segments

Permissions and Execution (Unix)

On Unix-like systems, a file must have executable permissions:

chmod +x myscript
./myscript

Use ls -l to see permission flags:

-rwxr-xr-- 1 user group 1234 date myscript

Executable vs Script

Portable Executables

A portable executable is a compiled program designed to run from any location without needing installation.

Examples:

• Portable apps on USB drives
• .exe files with embedded dependencies
• AppImage (Linux)

Executables in Different Languages

Running Executables

Windows:

Double-click in Explorer or run via Command Prompt:

C:\> myprogram.exe

Linux/macOS:

Mark as executable and run:

chmod +x myprogram
./myprogram

Cross-platform launchers:

• .jar: java -jar myapp.jar
• .py: python myscript.py

Security Considerations

• Executable files can carry malware — always verify the source.
• Use digital signatures to validate authorship.
• Antivirus software scans executables before and during execution.
• Executable exploits often target buffer overflows, DLL hijacking, etc.

Best Practices:

• Avoid running untrusted executables.
• Use sandboxing/virtual machines for risky software.
• Employ code signing and checksums for integrity.

Tools for Inspection and Debugging

Related Terms

• Compiler
• Linker
• Binary
• Interpreter
• Script
• Cross-compilation
• Debugging Symbols
• Dynamic Linking
• Static Linking
• Executable Header

Summary

An executable is the final product of software compilation: a binary file ready to be launched and run by the operating system. Whether you’re developing in C++, Rust, or Go, producing and understanding executables is essential for deploying performant and secure applications.

From file formats to OS compatibility, permissions, and runtime behavior, executables represent the transition from human logic to machine action.