GCC is a large codebase that has developed over a period of several decades, works on many different architectures, has had many contributors, and is itself written in several different languages.

Building GCC is similar to building many other large codebases. Since the people working on this project are themselves experts in compilers and build tools, the software has a high-quality build system.

The GCC source is available from four places: 1. As a git repository on gcc.gnu.org 2. As a weekly snapshot of the current development version 3. As official releases 4. Via a read-only mirror of the gcc.gnu.org repository on GitHub

Of these sources, I recommend using #1 or possibly #4 for development work. Clone the repository to your local machine as usual using standard git commands.

The GCC source code may be built inside the source directories, but this is not recommended and strongly discouraged by the GCC developers.

Instead, you should create a separate build directory. From this build directory, you should invoke the configure script which is in the root directory of the source repository.