toolchain/55439: Reduce redudnancy by separating arch and platform

[cmhanson%eschatologist.net@localhost]

>Number:         55439
>Category:       toolchain
>Synopsis:       Reduce redudnancy by separating arch and platform
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 30 23:15:00 +0000 2020
>Originator:     Chris Hanson
>Release:        netbsd-9
>Organization:
>Environment:
N/A
>Description:
NetBSD right now treats all of the platforms it supports as architectures, probably for historical reasons. However, there is a large amount of overlap between architectures that could be eliminated if there was more explicit separation.

As an example, there are a large numer of platforms such as hp300, mac68k, atari, amiga, sun3, x68k, and so on that all use the common m68k CPU architecture. A build of NetBSD for any one of these platforms should consist of building the platform-neutral m68k-architecture components and a separate build of the platform-specific components (such as drivers for unique hardware and first/second-stage bootstrap). A subsequent build of the same NetBSD tree for another one of these same platforms should only build the platform-specific components. And of course the platform-neutral and platform-specific components should be in separate installation sets as well (as should components that are both platform- and architecture-neutral).

The end result of taking this to its logical conclusion would be to build virtually all of the bits for a particular CPU architecture once, in an entirely generic fashion, including the GENERIC and INSTALL kernels thesmelves and many of the kernel modules. Only modules for platform-specific device drivers and code platform-specific first/second-stage bootstrapping would need to be built for the individual platforms.

It seems like the ARM-based platforms are at least partly doing things now; this would essentially make the strategy explicit and expand it to other platforms.
>How-To-Repeat:
N/A
>Fix:
N/A