CO-RE Documentation

[shaneutt]

Compile Once Run Everywhere (CO-RE) is an important facility of eBPF that enables something that most eBPF developers will in time expect to take for granted. However, at the time of writing there are very few places to find documentation on this. Mostly docs and news articles:

• https://facebookmicrosites.github.io/bpf/blog/2020/02/19/bpf-portability-and-co-re.html
• https://lwn.net/Articles/909095/#extending-the-programming-environment-past-full-c
• https://blog.aquasec.com/ebf-portable-code

(non-exhaustive)

But ultimately a "landing page" for CO-RE is missing from https://docs.kernel.org. I surmise that CO-RE is a pretty important feature that new eBPF developers want to learn about right away, and so the purpose of this issue is to suggest we add such a "landing page" which would provide readers with a strong explanation of what it is, and how its implemented in the kernel followed by how it works in Aya as I feel this would be a page that will get a lot of traffic from the greater eBPF community to come to Aya to learn more, and perhaps also interest them in trying out Aya if they haven't already.