Mastering GCC: From C Source to ELF Executable in Four Steps

Introduction

Computer programming languages are divided into machine language, assembly language, and high‑level languages. High‑level languages must be translated into machine code, either by a compiler (e.g., C, C++, Java) or an interpreter (e.g., Python, Ruby, MATLAB, JavaScript). This article explains how a C/C++ program is turned into processor‑executable binary code using the GCC toolchain.

GCC Toolchain Overview

GCC (GNU Compiler Collection) is the standard compilation suite on Linux. The toolchain consists of gcc , the binutils collection (including addr2line, ar, objcopy, objdump, as, ld, readelf, size, etc.), and the C runtime library.

Four‑Step Build Process

Preprocessing – expands macros, processes #include and conditional directives, removes comments, adds line numbers, and retains #pragma directives. Example command: $ gcc -E hello.c -o hello.i Compilation – performs lexical, syntactic, and semantic analysis on the preprocessed file and generates assembly code. Example command: $ gcc -S hello.i -o hello.s Assembly – translates assembly into object files ( .o) using as or gcc -c. Example commands:

$ gcc -c hello.s -o hello.o

$ as -c hello.s -o hello.o

Linking – combines object files and libraries into an ELF executable. Supports static linking ( -static) and dynamic linking. Example commands and size comparison:

$ gcc hello.c -o hello

$ size hello

$ ldd hello

$ gcc -static hello.c -o hello

$ size hello

$ ldd hello

Analyzing the ELF File

After linking, the result is an ELF (Executable and Linkable Format) file composed of sections such as .text, .rodata, .data, .bss, and .debug. The following command lists section headers: $ readelf -S hello Key sections: .text – executable code. .rodata – read‑only data (constants). .data – initialized global/static variables. .bss – uninitialized global/static variables. .debug – debugging symbols.

Disassembling the ELF

Because an ELF file cannot be opened as plain text, use objdump to view its instructions. Full disassembly: $ objdump -D hello Mixed source and assembly view (requires -g when compiling):

$ gcc -o hello -g hello.c

$ objdump -S hello

The output shows each C line alongside its generated machine instructions, making it easy to trace how source maps to binary.