Understanding the Compilation Process with GCC

What is GCC?

GCC stands for GNU Compiler Collection.The GNU Compiler Collection, commonly known as GCC, is a set of compilers and development tools available for Linux, Windows, various BSDs, and a wide assortment of other operating systems. It includes support primarily for C and C++ and includes Objective-C, Ada, Go, Fortran, and D. The Free Software Foundation (FSF) wrote GCC and released it as completely free (as in libre) software.

How does it work?

GCC is a toolchain that compiles code, links it with any library dependencies, converts that code to assembly, and then prepares executable files. It follows the standard UNIX design philosophy of using simple tools that perform individual tasks well. The GCC development suite utilizes these discrete tools to compile software. When you run GCC on a source code file, it first uses a preprocessor to include header files and discard comments. Next, it tokenizes the code, expands macros, detects any compile-time issues, then prepares it for compilation. It is then sent to the compiler, which creates syntax trees of the program’s objects and control flow and uses those to generate assembly code. The assembler then converts this code into the binary executable format of the system. Finally, the linker includes references to any external libraries as needed. The finished product is then executable on the target system.

Compilers

Play a vital role in software development by transforming human-readable source code into machine-executable code. The GNU Compiler Collection (GCC) is a popular and powerful compiler that can compile code written in various programming languages. In this blog post, we'll explore the steps of compilation using GCC, illustrated with command-line examples.

The Compilation Process

The compilation process carried out by GCC Compiler consists in four steps: preprocessing, compilation, assemble, and linking

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1.Preprocessing:

At this stage, the preprocessor handles directives starting with '#' in your source code. These directives include to include header files, for macros, and more. The preprocessor expands macros and includes the content of header files.

2.Compilation:

The compiler proper translates the preprocessed source code (in the form of an intermediate file) into assembly code specific to the target platform.

3.Assembly:

In this step, the assembly code is converted into machine code. GCC generates an assembly file (with a '.s' extension), which is then passed to an assembler to create an object file (with a '.o' extension)

4.Linking:

The final step is linking, where the object files generated in the previous step are combined into a single executable file. During this process, unresolved references to functions or variables are resolved. Libraries and runtime support code are also linked to the executable.

Practical Example

Let's demonstrate the compilation process using a simple C program. Here's our source code, "hello.c":

Preprocessing

The above command generates the preprocessed source code in "hello.i," which includes the contents of the header file.

Compilation

This command compiles "hello.i" into assembly code stored in "hello.s."

Assembly

The assembly code in "hello.s" is assembled into an object file "hello.o."

Linking

Finally, the object file "hello.o" is linked to create the executable "hello."

Now, you can run your program

This simple example illustrates the compilation process with GCC, from preprocessing to linking. Understanding these steps is crucial for software developers, as it enables them to debug, optimize, and analyze their code effectively.

In conclusion, GCC is a versatile and powerful compiler that simplifies the complex process of transforming source code into executables. By breaking down the compilation process into distinct steps, developers can gain a deeper understanding of how their code is transformed into machine-executable instructions. This knowledge is essential for producing efficient, error-free software.

Thanks for reading.