Where can I find good open source code flow visualization software?

Question

I am working on an academic research regarding some very long functions in the Linux kernel (link, link).

For that research, I would like to use some code flow visualiza

Answer 1

You appears to want to acquire a flowchart of C source code ("decisions", "code blocks").
Something like this C flowchart?

To do this correctly, esp. for Linux kernal code, I'd expect you to have to preprocess the code first to get rid of macros and conditionals. I would assume that GCC would construct such a graph internally and that you ought to be able to get your hands on that graph.