One of the most fun work projects I had early in my career was writing a linker for PE files for an embedded PLC. Another team was writing some gcc compiler ex

One of the most fun work projects I had early in my career was writing a linker for PE files for an embedded PLC. Another team was writing some gcc compiler extensions and an emulator for the PLC that ran on Window's PCs with all the emulator code stored in DLLs. The idea was pretty cool - you could write and test ladder logic in a Window's GUI and then click a button to generate an .exe file and upload it to the PLC. The PLC's RTOS would then call my linker code which would link up the symbol tables for the DLLs with the embedded code in the PLC and do some other minor relocations. By putting all the ladder logic code in the loaded .exe they were able to optimize for size/speed (using gcc and heuristics of the ladder logic diagram) instead of running a ladder logic interpreter in the PLC. If you ever get a change to play around with a linker I'd suggest you do. It's one of those "aha" moments in CS about the userland/OS boundary.