Ask HN: What is everything that can be known about a C program?

I've been browsing through some C references, noticing tools and such. And I've been wondering: What is everything that can be known about a C program? What tools are needed to get the information. What can you do with the information? If you're not sure which category your tool/technique is in, just pick one, or don't bother categorizing it. Some categories: - Environment, before a line is written. Not including anything below. - During/after edit, before compiling. What can the source tell you? - During "building:" compiling, linking, making, configuring. - After building, before execution. - During execution. - During debugging. The debugger is not the only debugging tool. - After execution/debugging.