proposal: add package debug/goobj

[josharian]

We have code scattered around that knows about the insides of cmd/compile's object files, in the compiler, the go/types importer, the linker, and some packages in x/tools. It'd be nice to consolidate this knowledge a bit, because the object files are non-trivial and they change over time, and the versioning support is non-trivial.

It's unfortunate to add API surface area in the main repo, but it seems like the natural place for it. Most of the shared implementation for the toolchain and go/types could be in an internal package, with minimal API exposed at debug/goobj as strictly needed for external tools. See CL 41053 for one such use.

This proposal obviously needs fleshing out, but I want to get an initial pulse before putting in much effort on the design.

cc @griesemer

[josharian]

On reflection, probably the right solution here is #14386.

[rsc]

Yes, I'd like to avoid debug/goobj in the standard library. The one we use for cmd is internal for a reason.

[rsc]

Let's leave things as they are for now until we've cleaned up the object format (which is not a high priority right now - nothing is slowing us down significantly).