How UPX works?

I want to make a wrapper/loader. I know UPX does this, but it also encrypts/compresses, which I don't need. I'm not proficient enough to understand all of UPX's source code.

Here's what I want to be able to do:

1. Write the loader in C++
2. The loader would contain another executable inside of it (at the end of the file)
3. It would read from itself at runtime, and extract the EXE data from the end, and run it

But, it would need to do this without writing the 2nd EXE to disk first, and then launching.

It would do it all from RAM.

Does anyone know how this works?

I'm wanting to eventually make something like this:
EXE Protector
http://www.planet-source-code.com/vb...58026&lngWId=1

But open-source. That one doesn't contain the source code to the loader. :mad:

If something like this isn't allowed here, maybe someone can PM me with info?

Thanks.