Question

I’m trying to learn x86. I thought this would be quite easy to start with – i’ll just compile a very small program basically containing nothing and see what the compiler gives me. The problem is that it gives me a ton of bloat. (This program cannot be run in dos-mode and so on) 25KB file containing an empty main() calling one empty function.

How do I compile my code without all this bloat? (and why is it there in the first place?)

Answer 1

Executable formats contain a bit more than just the raw machine code for the CPU to execute. If you want that then the only option is (I think) a DOS .com file which essentially is just a bunch of code loaded into a page and then jumped into. Some software (e.g. Volkov commander) made clever use of that format to deliver quite much in very little executable code.

Anyway, the PE format which Windows uses contains a few things that are specially laid out:

• A DOS stub saying “This program cannot be run in DOS mode” which is what you stumbled over
• several sections containing things like program code, global variables, etc. that are each handled differently by the executable loader in the operating system
• some other things, like import tables

You may not need some of those, but a compiler usually doesn’t know you’re trying to create a tiny executable. Usually nowadays the overhead is negligible.

There is an article out there that strives to create the tiniest possible PE file, though.