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Re: cross-compiling philosophy

From: Larry Doolittle
Subject: Re: cross-compiling philosophy
Date: Wed, 29 Oct 2003 12:55:36 -0800
User-agent: Mutt/

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
   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 for screen-3.9.15
and you'll see the motivation for my suggestions.

       - Larry

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