sys: add type safe Pointer wrapper

[lmb]

Add TypedPointer which is a type safe wrapper around Pointer. This relieves users of the generated bindings from knowing which types are expected. This should make it less likely that we cause a hard to debug panic or crash due to the kernel overwriting runtime memory.

sys.Pointer still exists because there are some cases where we legitimately don't know what type to point at, for example the link info APIs. Map APIs are also unchanged for now because they don't benefit much from converting to TypedPointer[byte].

[lmb]

The breaking change is due to replacing ebpf.MapID and ProgramID with a type alias.

[kolyshkin]

I like the approach!

It will be better to separate the actual overrun fix from the new type system.

I've also updated the fix in #1660 to not break the existing API nor return truncated pointers, PTAL @lmb

[dylandreimerink]

I like this! More type safety more better

[ti-mo]

@lmb Looks like this implements #914?

[ti-mo]

Wouldn't this allow us to unexport sys.Pointer? Ie. if it needs to be used outside of the package, it needs to be wrapped in an (Unsafe/Typed/String/XYZ)Pointer. Then we make sure UAPI no longer takes any sys.Pointers.

I still see a bunch of sys.Pointer uses in the map API; I'd argue those should all be sys.UnsafePointers instead, to be converted to typed pointers before returning.

[lmb]

I still see a bunch of sys.Pointer uses in the map API; I'd argue those should all be sys.UnsafePointers instead, to be converted to typed pointers before returning.

Discussed face to face: UnsafePointer is a constructor, not a type. We still need sys.Pointer to account for endianness differences on 32 bit arches.

Discussed f2f