Re: cross-compiling philosophy

[Larry Doolittle]

Guido -

Thanks for taking the time to respond.

> I am into the crosscompiling thing a lot, and in fact
> the most common targets are embedded platforms which
> can not bear a full fledged development environment.
> Those could not benefit quite from your proposal
> unless they are big enough to run a compiler which
> in turn has access to a well-sized filesystem, and
> all in all with a full network stack in the system,
> and processing power enough to get an answer in
> a reasonable roundtrip time. See the problem?

I understand many embedded targets are smaller and
less featureful than what I work with.  The hoo-hah
in the media between Windows/CE and Linux for the
embedded market is some indication that larger embedded
targets are becoming common.

My system _might_ be big enough to self-host the compiler,
but given the choice of building on a
   2 GHz Athlon, 512M RAM, local disks
vs.
   200 MHz StrongARM, 32M RAM, NFS disks
I'll take the workstation.

In order to run tests on the embedded target, all it takes
(which I have) is a running Linux system with networking,
so I can telnet in and NFS mount disks.

If my system doesn't sound adequately embedded to you,
consider its size: it measures 26 x 61 mm, and runs off
of 3.3 V @ 600 ma.

> There are quite some provisions within autoconf to
> help in crosscompiling, most of the standard tests
> work via cache-variables that you could override in
> a CONFIG_SITE script. Oh well, that option is not
> known all too well.

I know about it, and use it.  But that doesn't help
me when third-party-software-authors don't use it, or
need tests not covered by the standard list.

> It does help with most of the
> smaller crosscompiled applications. And if you have
> an application with its own handmade configure-time
> run-tests then you need to modify them to pick up
> some shell-var (or better a cache-var) to make things
> easier for you - and allow you to create multiple
> config-site scripts for your various platforms that
> you target.

That is much slower and more error prone than actually
checking the response of the system, which is (after all)
the whole point of autoconf.  Since I _can_ ask the
embedded system what its behavior is, isn't that
the best option?

> Still, there are few things missing in the autotools
> series to support crosscompiling for the better, in
> the sense to get away with it and _without_ manually
> checking a cache-var file. A lot can be done now
> but some things are still missing, and if I had only
> time then I'd try to write up some patches myself.
> However, I am also one of those who do already have
> proper config-site files, so why investing time on
> other stuff *sigh*

Take a look at config.in for screen-3.9.15
   http://www.gnu.org/software/screen/
and you'll see the motivation for my suggestions.

       - Larry