Understanding drivers and toolchains in Clang

Before we talk about the compiler driver in Clang, it is necessary to highlight the fact that compiling a piece of code is never a single task (and not a simple one, either). In school, we were taught that a compiler consists of a lexer, a parser, sometimes came with an optimizer, and ended with an assembly code printer. While you still can see these stages in real-world compilers, they give you nothing but textual assembly code rather than an executable or library, as we would normally expect. Furthermore, this naïve compiler only provides limited flexibility – it can't be ported to any other operating systems or platforms.

To make this toy compiler more realistic and usable, many other plumber tools need to be put together, along with the core compiler: an assembler to transform assembly code into (binary format) object file, a linker to put multiple object files into an executable or library, and many other routines...