Host settings for GNU in configure*?

[Svante Signell]

Hi,

I know that may of you are at GHM the rest of this week but anyway.

When porting packages to GNU/Hurd sometimes $host and $host_os in
configure are set differently:

$host: 
When specified i486-pc-gnu
>From config.guess/ in autotools-dev: i686-unknown-gnu0.3

Examples:
/usr/share/misc/config.guess
i686-unknown-gnu0.3
/usr/share/misc/config.sub i486-gnu
i486-pc-gnu
/usr/share/misc/config.sub i686-unknown-gnu0.3
i686-unknown-gnu0.3

Linux:
/usr/share/misc/config.guess               
i686-pc-linux-gnu
/usr/share/misc/config.sub i686-linux
i686-pc-linux-gnu

Maybe config.guess should be updated:
/usr/share/misc/config.guess
i{4,6}86-pc-gnu0.3
or 
i{4,6}86-pc-gnu

$host_os:
gnu when specified
gnu0.3 from config.guess

Some questions arises immediately:

1) Where to find the specification resulting in i486-pc-gnu?
2) What are the roles of config.guess/config.sub from autotools-dev? 
3) How to specify gnu uniquely in configure and configure.ac?
Example: configure.ac
*-linux*|*-k*bsd-gnu) action;; ->  *-linux*|*-k*bsd-gnu|"gnu here") action;;

A common denominator of $host is

a) i*86*-gnu*
b) i*86-*-gnu*
c) *-gnu*
d) Other variants?

4) Should the identifier be unique?
Since linux can be i486-linux-gnu and kfreeebsd
i686-unknown-kfreebsd8.1-gnu neither version is unique.
5) Is it OK if placed last?

Debian specific
===============
Sometimes debian/rules for a package contains:

DEB_HOST_ARCH_OS := $(shell dpkg-architecture -qDEB_HOST_ARCH_OS)
DEB_HOST_GNU_TYPE=$(shell dpkg-architecture -qDEB_HOST_GNU_TYPE)
DEB_BUILD_GNU_TYPE=$(shell dpkg-architecture -qDEB_BUILD_GNU_TYPE)

resulting in: hurd, i486-gnu, i486-gnu respectively.

6) Are these only local to the rules file?