Implement breakpoints and single-stepping of userspace processes

[bollu]

Hey, thanks for this really cool library!

I was wondering if drgn plans to support the ability to not just debug programs (a) after-the-fact via a core dump, (b) connect to long-running programs via their PID, but also support GDB/LLDB like use-cases that allows (c) single-stepping through an executable.

It'd be really helpful to have a scriptable, pure python library/REPL to single-step through a program. Is it possible to use drgn for this purpose? If so, pointers on how to do this would be swell. If not, is it possible to extend drgn to support this?

[osandov]

This isn't currently supported, but it's definitely planned. The plan is to first add an API to represent threads (#92), which @Svetlitski-FB is currently working on. Once that's done, we can add APIs for attaching to threads, setting breakpoints, and stepping. I don't have an estimate of when that will be done.