> The platform 4-tuple is stolen from
> <https://wiki.debian.org/Multiarch/Tuples> as faithfully as possible
> (currently, not very). If you go to that page, they have done an
> excellent job mapping loads of 4-tuples covering numerous platforms. We
> should probably just adopt their approach.
>
> So their 4-tuple is (kernel userland computer endian) as above.

I didn't explain myself properly. The IDs on that page are written like:

mips64el-linux-gnuabin32

So that's only three components. But mips64el means MIPS64 and
little-endian, so that's two components of the 4-tuple joined into one.

Their table also has a fifth column for the word size (32 or 64); it's
up for debate whether it should be part of the CPU architecture name or
be separate. I don't have an opinion and would be interested in hearing
arguments for either choice.