Learn Assembly if you are REALLY curious what really takes place under the hood. AS — the portable GNU assembler.
AS uses the traditional UNIX® assembly language syntax, NOT Intel syntax. It comes with the system.
$ which as /usr/bin/as
$ as --version GNU assembler (GNU Binutils for Ubuntu) 2.30 Copyright (C) 2018 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `x86_64-linux-gnu'.