GCC - GNU Compiler Collection

The GNU Compiler Collection (GCC) stands as one of the most influential and widely-used compiler systems in the history of computing. Originally created by Richard Stallman in 1987 as the GNU C Compiler, GCC has evolved into a comprehensive collection of compilers supporting multiple programming languages including C, C++, Objective-C, Fortran, Ada, Go, and D. As the official compiler for GNU and Linux systems, GCC has played a pivotal role in the development of free and open-source software, providing the foundation for countless applications, operating systems, and embedded systems worldwide. Its robust optimization capabilities, extensive platform support, and adherence to language standards have made it the compiler of choice for everything from small embedded projects to large-scale enterprise applications and high-performance computing systems.

Installation and Setup

Installing GCC on Different Platforms

# Ubuntu/Debian installation
sudo apt update
sudo apt install gcc g++ build-essential

# Install specific version
sudo apt install gcc-11 g++-11

# Install development tools
sudo apt install libc6-dev linux-libc-dev

# CentOS/RHEL/Fedora installation
sudo dnf groupinstall "Development Tools"
sudo dnf install gcc gcc-c++

# Or using yum (older systems)
sudo yum groupinstall "Development Tools"
sudo yum install gcc gcc-c++

# macOS installation (via Xcode Command Line Tools)
xcode-select --install

# Or using Homebrew
brew install gcc

# Windows installation (MinGW-w64)
# Download from https://www.mingw-w64.org/
# Or using MSYS2
pacman -S mingw-w64-x86_64-gcc

# Verify installation
gcc --version
g++ --version

# Check supported languages
gcc --help=target

# List all installed GCC versions
ls /usr/bin/gcc*

# Set default version (Ubuntu/Debian)
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 60
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-11 60

GCC Configuration and Environment

# Environment variables
export CC=gcc
export CXX=g++
export CFLAGS="-O2 -Wall"
export CXXFLAGS="-O2 -Wall -std=c++17"

# Cross-compilation setup
export CC=arm-linux-gnueabihf-gcc
export CXX=arm-linux-gnueabihf-g++

# Library paths
export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$PKG_CONFIG_PATH

# Include paths
export C_INCLUDE_PATH=/usr/local/include:$C_INCLUDE_PATH
export CPLUS_INCLUDE_PATH=/usr/local/include:$CPLUS_INCLUDE_PATH

# Check GCC configuration
gcc -v
gcc -dumpmachine
gcc -dumpversion

# Show default include paths
gcc -E -v - </dev/null
g++ -E -v - </dev/null

# Show default library paths
gcc -print-search-dirs

# Show built-in defines
gcc -dM -E - </dev/null

# Show supported targets
gcc --print-targets

# Show supported multilib
gcc -print-multi-lib

Basic Compilation

Simple Compilation Commands

# Compile C program
gcc hello.c -o hello
gcc -o hello hello.c

# Compile C++ program
g++ hello.cpp -o hello
g++ -o hello hello.cpp

# Compile without linking (object file only)
gcc -c source.c
g++ -c source.cpp

# Compile multiple source files
gcc file1.c file2.c file3.c -o program
g++ file1.cpp file2.cpp file3.cpp -o program

# Link object files
gcc file1.o file2.o file3.o -o program

# Compile and run in one line
gcc hello.c -o hello && ./hello

# Compile with specific C standard
gcc -std=c99 program.c -o program
gcc -std=c11 program.c -o program
gcc -std=c17 program.c -o program

# Compile with specific C++ standard
g++ -std=c++11 program.cpp -o program
g++ -std=c++14 program.cpp -o program
g++ -std=c++17 program.cpp -o program
g++ -std=c++20 program.cpp -o program

# Compile for different architectures
gcc -m32 program.c -o program32    # 32-bit
gcc -m64 program.c -o program64    # 64-bit

# Generate assembly output
gcc -S source.c                    # Creates source.s
gcc -S -o output.s source.c

# Generate preprocessed output
gcc -E source.c                    # Output to stdout
gcc -E source.c -o source.i        # Save to file

# Verbose compilation
gcc -v source.c -o program

# Show compilation commands without executing
gcc -### source.c -o program

Compilation Stages

# Four stages of compilation: preprocessing, compilation, assembly, linking

# Stage 1: Preprocessing (cpp)
gcc -E source.c -o source.i
cpp source.c source.i

# Stage 2: Compilation (cc1)
gcc -S source.i -o source.s
gcc -S source.c -o source.s

# Stage 3: Assembly (as)
gcc -c source.s -o source.o
as source.s -o source.o

# Stage 4: Linking (ld)
gcc source.o -o program
ld source.o -o program

# Stop after specific stage
gcc -E source.c                    # Stop after preprocessing
gcc -S source.c                    # Stop after compilation
gcc -c source.c                    # Stop after assembly

# Save intermediate files
gcc -save-temps source.c -o program

# Use specific tools
gcc -B/path/to/tools source.c      # Use tools from specific directory

Optimization Options

Optimization Levels

# No optimization (default, fastest compilation)
gcc -O0 source.c -o program

# Basic optimization (good balance)
gcc -O1 source.c -o program

# Standard optimization (recommended for most cases)
gcc -O2 source.c -o program

# Aggressive optimization (may increase compilation time)
gcc -O3 source.c -o program

# Optimize for size
gcc -Os source.c -o program

# Optimize for fast compilation
gcc -Ofast source.c -o program

# Optimize for debugging
gcc -Og source.c -o program

# Profile-guided optimization (two-step process)
# Step 1: Compile with profiling
gcc -O2 -fprofile-generate source.c -o program
./program  # Run with representative input
# Step 2: Compile with profile data
gcc -O2 -fprofile-use source.c -o program_optimized

# Link-time optimization
gcc -O2 -flto source1.c source2.c -o program

# Specific optimization flags
gcc -O2 -funroll-loops source.c -o program
gcc -O2 -finline-functions source.c -o program
gcc -O2 -fomit-frame-pointer source.c -o program

Advanced Optimization

# Vectorization
gcc -O2 -ftree-vectorize source.c -o program
gcc -O3 -march=native source.c -o program

# Loop optimizations
gcc -O2 -funroll-loops source.c -o program
gcc -O2 -funroll-all-loops source.c -o program
gcc -O2 -fpeel-loops source.c -o program

# Function inlining
gcc -O2 -finline-functions source.c -o program
gcc -O2 -finline-small-functions source.c -o program
gcc -O2 -finline-functions-called-once source.c -o program

# Architecture-specific optimization
gcc -O2 -march=native source.c -o program
gcc -O2 -march=skylake source.c -o program
gcc -O2 -mtune=generic source.c -o program

# Show optimization report
gcc -O2 -fopt-info source.c -o program
gcc -O2 -fopt-info-vec source.c -o program
gcc -O2 -fopt-info-loop source.c -o program

# Disable specific optimizations
gcc -O2 -fno-inline source.c -o program
gcc -O2 -fno-unroll-loops source.c -o program

# Optimization for specific use cases
gcc -O2 -ffast-math source.c -o program        # Fast math (may reduce precision)
gcc -O2 -fno-math-errno source.c -o program    # Don't set errno for math functions
gcc -O2 -funsafe-math-optimizations source.c -o program

Warning and Error Options

Warning Levels

# Basic warnings
gcc -Wall source.c -o program

# Extra warnings
gcc -Wextra source.c -o program

# All warnings
gcc -Wall -Wextra source.c -o program

# Treat warnings as errors
gcc -Werror source.c -o program

# Specific warning categories
gcc -Wpedantic source.c -o program             # Strict ISO C compliance
gcc -Wconversion source.c -o program           # Type conversion warnings
gcc -Wshadow source.c -o program               # Variable shadowing
gcc -Wunused source.c -o program               # Unused variables/functions
gcc -Wuninitialized source.c -o program       # Uninitialized variables
gcc -Wformat source.c -o program               # Format string checking
gcc -Wcast-align source.c -o program          # Cast alignment issues
gcc -Wwrite-strings source.c -o program       # String literal modifications

# Disable specific warnings
gcc -Wall -Wno-unused-variable source.c -o program
gcc -Wall -Wno-format source.c -o program

# C++-specific warnings
g++ -Wall -Weffc++ source.cpp -o program      # Effective C++ guidelines
g++ -Wall -Wold-style-cast source.cpp -o program
g++ -Wall -Woverloaded-virtual source.cpp -o program

# Enable additional useful warnings
gcc -Wall -Wextra -Wpedantic -Wformat=2 -Wconversion \
    -Wshadow -Wunused -Wuninitialized -Wcast-align \
    -Wwrite-strings source.c -o program

# Show all available warnings
gcc --help=warnings

Error Handling

# Stop on first error
gcc -Wfatal-errors source.c -o program

# Maximum number of errors
gcc -fmax-errors=5 source.c -o program

# Colorized output
gcc -fdiagnostics-color=always source.c -o program
gcc -fdiagnostics-color=auto source.c -o program

# Show column numbers in diagnostics
gcc -fdiagnostics-show-location=every-line source.c -o program

# Show option that triggered warning
gcc -fdiagnostics-show-option source.c -o program

# Template backtrace limit (C++)
g++ -ftemplate-backtrace-limit=0 source.cpp -o program

# Syntax-only check (no compilation)
gcc -fsyntax-only source.c

# Check for undefined behavior
gcc -fsanitize=undefined source.c -o program

Debugging and Profiling

Debug Information

# Generate debug information
gcc -g source.c -o program

# Different debug levels
gcc -g0 source.c -o program        # No debug info
gcc -g1 source.c -o program        # Minimal debug info
gcc -g2 source.c -o program        # Default debug info
gcc -g3 source.c -o program        # Maximum debug info

# Debug format options
gcc -gdwarf-4 source.c -o program   # DWARF version 4
gcc -gstabs source.c -o program     # Stabs format

# Debug with optimization
gcc -O2 -g source.c -o program

# Split debug information
gcc -g -gsplit-dwarf source.c -o program

# Compressed debug sections
gcc -g -gz source.c -o program

# Debug macros
gcc -g3 -gdwarf-4 source.c -o program

# Address sanitizer
gcc -g -fsanitize=address source.c -o program

# Memory sanitizer
gcc -g -fsanitize=memory source.c -o program

# Thread sanitizer
gcc -g -fsanitize=thread source.c -o program

# Undefined behavior sanitizer
gcc -g -fsanitize=undefined source.c -o program

# Leak sanitizer
gcc -g -fsanitize=leak source.c -o program

Profiling Support

# Generate profiling information
gcc -pg source.c -o program
./program
gprof program gmon.out > analysis.txt

# Coverage testing
gcc --coverage source.c -o program
./program
gcov source.c
lcov --capture --directory . --output-file coverage.info
genhtml coverage.info --output-directory coverage_html

# Profile-guided optimization
gcc -fprofile-generate source.c -o program
./program  # Run with representative data
gcc -fprofile-use source.c -o program_optimized

# Time profiling
gcc -ftime-report source.c -o program

# Memory usage profiling
gcc -fmem-report source.c -o program

# Stack usage analysis
gcc -fstack-usage source.c -o program

Libraries and Linking

Static and Dynamic Linking

# Link with standard libraries
gcc source.c -lm -o program         # Math library
gcc source.c -lpthread -o program   # POSIX threads
gcc source.c -ldl -o program        # Dynamic loading

# Link with custom libraries
gcc source.c -L/path/to/lib -lmylib -o program

# Static linking
gcc -static source.c -o program

# Create static library
ar rcs libmylib.a file1.o file2.o file3.o

# Create shared library
gcc -shared -fPIC file1.c file2.c -o libmylib.so

# Link with shared library
gcc source.c -L. -lmylib -o program

# Set runtime library path
gcc source.c -L/path/to/lib -lmylib -Wl,-rpath,/path/to/lib -o program

# Show library dependencies
ldd program

# Link order matters
gcc source.c -lmylib -lm -o program

# Whole archive linking
gcc -Wl,--whole-archive -lmylib -Wl,--no-whole-archive source.c -o program

# Version script for shared libraries
gcc -shared -Wl,--version-script=version.map file1.c -o libmylib.so

Include Paths and Preprocessor

# Add include directories
gcc -I/path/to/headers source.c -o program
gcc -I. -I../include source.c -o program

# System include directories
gcc -isystem /path/to/system/headers source.c -o program

# Define preprocessor macros
gcc -DDEBUG source.c -o program
gcc -DDEBUG=1 source.c -o program
gcc -DVERSION=\"1.0\" source.c -o program

# Undefine macros
gcc -UDEBUG source.c -o program

# Include file directly
gcc -include config.h source.c -o program

# Show include search paths
gcc -E -v - </dev/null

# Dependency generation
gcc -M source.c                     # Generate dependencies
gcc -MM source.c                    # Generate dependencies (no system headers)
gcc -MD source.c -o program         # Compile and generate dependencies
gcc -MMD source.c -o program        # Compile and generate dependencies (no system headers)

Cross-Compilation

Target Architecture

# Install cross-compilation toolchain
sudo apt install gcc-arm-linux-gnueabihf
sudo apt install gcc-aarch64-linux-gnu
sudo apt install gcc-mingw-w64

# Cross-compile for ARM
arm-linux-gnueabihf-gcc source.c -o program_arm

# Cross-compile for ARM64
aarch64-linux-gnu-gcc source.c -o program_arm64

# Cross-compile for Windows
x86_64-w64-mingw32-gcc source.c -o program.exe

# Specify target explicitly
gcc -target arm-linux-gnueabihf source.c -o program_arm

# Set sysroot for cross-compilation
gcc --sysroot=/path/to/target/sysroot source.c -o program

# Cross-compilation environment variables
export CC=arm-linux-gnueabihf-gcc
export CXX=arm-linux-gnueabihf-g++
export AR=arm-linux-gnueabihf-ar
export STRIP=arm-linux-gnueabihf-strip

# Configure for autotools
./configure --host=arm-linux-gnueabihf --prefix=/usr/local/arm

# CMake cross-compilation
cmake -DCMAKE_TOOLCHAIN_FILE=arm-toolchain.cmake ..

Embedded Systems

# Compile for bare metal (no OS)
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb source.c -o program.elf

# Specify memory layout
arm-none-eabi-gcc -T linker_script.ld source.c -o program.elf

# Generate binary file
arm-none-eabi-objcopy -O binary program.elf program.bin

# Generate hex file
arm-none-eabi-objcopy -O ihex program.elf program.hex

# Size information
arm-none-eabi-size program.elf

# Disassemble
arm-none-eabi-objdump -d program.elf

# Common embedded flags
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -mfloat-abi=hard \
    -mfpu=fpv4-sp-d16 -Os -ffunction-sections -fdata-sections \
    -Wl,--gc-sections source.c -o program.elf

Advanced Features

Language-Specific Options

# C-specific options
gcc -std=c99 -pedantic source.c -o program
gcc -std=gnu99 source.c -o program

# C++-specific options
g++ -std=c++17 -pedantic source.cpp -o program
g++ -std=gnu++17 source.cpp -o program

# Objective-C
gcc -x objective-c source.m -o program

# Mixed language compilation
gcc source.c module.cpp -lstdc++ -o program

# Enable specific language features
g++ -fconcepts source.cpp -o program           # C++20 concepts
g++ -fcoroutines source.cpp -o program         # C++20 coroutines
g++ -fmodules-ts source.cpp -o program         # C++20 modules

# Disable language features
g++ -fno-exceptions source.cpp -o program
g++ -fno-rtti source.cpp -o program

Security Features

# Stack protection
gcc -fstack-protector source.c -o program
gcc -fstack-protector-strong source.c -o program
gcc -fstack-protector-all source.c -o program

# Position independent code
gcc -fPIC source.c -o program
gcc -fPIE source.c -o program

# Fortify source
gcc -D_FORTIFY_SOURCE=2 -O2 source.c -o program

# Control flow integrity
gcc -fcf-protection source.c -o program

# Return address protection
gcc -mretpoline source.c -o program

# Address space layout randomization
gcc -fPIE -pie source.c -o program

# Relocation read-only
gcc -Wl,-z,relro,-z,now source.c -o program

# No execute stack
gcc -Wl,-z,noexecstack source.c -o program

Performance Analysis

# Generate assembly with C code comments
gcc -S -fverbose-asm source.c

# Show optimization decisions
gcc -O2 -fopt-info-vec-optimized source.c -o program
gcc -O2 -fopt-info-loop-optimized source.c -o program

# Benchmark compilation time
time gcc -O2 source.c -o program

# Memory usage during compilation
/usr/bin/time -v gcc -O2 source.c -o program

# Parallel compilation
make -j$(nproc)

# Use ccache for faster recompilation
ccache gcc source.c -o program

# Profile compilation
gcc -ftime-report -fmem-report source.c -o program

GCC's extensive feature set, mature optimization capabilities, and broad platform support make it an indispensable tool for software development across diverse domains. From simple command-line utilities to complex embedded systems and high-performance computing applications, GCC provides the reliability, performance, and flexibility needed to build robust software solutions. Its commitment to open standards, active development community, and comprehensive documentation ensure that GCC remains at the forefront of compiler technology, continuing to evolve with the changing needs of the software development landscape.