add gcov support

[khale]

It would be great to have gcov output for generating test coverage results and for general informational purpose. Supporting this in a running kernel will require some output channel over which gcov report files can be generated. Generally, I can see the following path for this:

• add -coverage flag to the flags for clang and gcc when we wan't to generate code coverage support
• add a build option in Kconfig for using gcov
• add runtime hooks for gcov (see here and search for gcov in the linux source tree (e.g. kernel/gcov/base.c))
• output gcov data over the qemu debug device using the debugcon=xxx flag
• build a tool to parse and separate the output from QEMU into gcov files
• integrate gcov output into CI tool (.travis.yaml)

[claudemuller]

Hi @khale

I'm trying to get into OSS dev, particularly C in order to improve my knowledge of said language. I would describe myself as a beginner in C (10+ years in JS, PHP, various languages like Go, Scala, Java and Python). So I was thinking to give this issue a go. It seems to cover a good amount different tasks that need to be integrated (also I've never written or run unit tests for C so that will be new too). Mind if I have a go (and bug you or anyone else for assistance if I get hopelessly stuck?)?

[khale]

Sure! Happy to have someone take a stab. Definitely check out the README and the CONTRIBUTING documents in the top-level.

[claudemuller]

100s! Thanks @khale I'll check those out and start getting to grips with the repo 👍