Tools like gdb and docgen are useful for smaller open source projects, but I think they quickly loose effectiveness on a large code base. For example I think the original post's high level view would work great when starting a new job as well as when diving into an open source project.
That said one step down the chain from stack traces and profiler output might be to look at log files, or run the code in verbose/debug/trace mode if it exists.
That said one step down the chain from stack traces and profiler output might be to look at log files, or run the code in verbose/debug/trace mode if it exists.