3998-byte executable reduced to 45 bytes

This article is definitely not intended to teach you how to optimize your programs. That is, unless your usual programs are small enough to embed inside object file headers with the opcodes overlapping header field values.

It's a clever hack that teaches you about how ELF works by forcing you to think carefully about every single byte in a customized ELF executable.

I work frequently with object file formats (especially ELF) and write tools which manipulate executables and libraries and when I first read this article about 5 years ago I learned more about ELF than from any other source.

Highly recommended!

The end result is not useful, but I learned a lot of new things about C and processes along the way.

And I thought it was an inspiring exercise to go as far down to the metal as possible.

It does make me feel guilty when programming Ruby that I sometimes create an entire array object to compare two integers because it looks prettier, without any regard for performance. It feels so wasteful.

That's an interesting point, and certainly true in some areas, but having thought about it, I don't think it's fair.

The point of theexercise is to reduce to the smallest bit of program.. Your version should count the size of the interpeter as well, since it's necessary for execution.

Under that model, I could use a program of

1

I'll run this program with my new SwankyCool intrepreter [tm] which returns 42 if it sees a program comprising only "1"; Otherwise it calls perl to exec the rest of the file.

Now, in both cases, we're accepting that the entire OS is already there, but that was stated in his example. (ELF on Linux)

This is an awesome old classic which is required reading for anybody who wants to understand how ELF object files are loaded and executed.

This is pretty far beyond 'optimization'. The executable is 7 bytes smaller than the minimum legal size for the object file header!