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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Access Type
Date: Wed, 29 Dec 2010 16:27:11 +0100
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Simon Wright writes:
> It's possible to have one compiler generate both 32- and 64-bit code;
> for an Intel target you can use -m32/-m64 (for example) provided the
> compiler was built with that ability. Whenever I've built a compiler
> it's been for one architecture only; if for no other reason than that
> the Ada build process in GCC doesn't support multilibs. (Well, that's
> what the documentation seemed to be saying ...)

Multilib support for libgnat was introduced in GCC 4.4.  This means the
ability to build both a 32-bit and a 64-bit version of libgnat and to
link the program against either.

Multiarch support was introduced earlier than that.  This means support
for -m32/-m64 and the ability to emit either 32- or 64-bit object code.

> I don't remember whether GNAT for PowerPC supports 64-bit, don't think
> so???

Yes, it does.

> It sounds as though your argument list ought to be an array of ints
> (or Integers), not bytes?

I'd rather call them "words".

> One thing you'll need to be careful of: some Ada features (eg
> exception handling, functions returing indefinite objects, tasking
> ...) rely on runtime support that may not be available, or may not be
> properly initialized, in the OFW environment. I'm not familiar with
> how to get over this sort of problem.

Right.  Since a bootloader runs without an underlying operating system,
I'd suggest adding the following configuration pragma to one of the
source files:

pragma No_Run_Time;

Then all you need is a 32-bit compiler.  Beware that memory management
will no longer be available (i.e. "new" and Unchecked_Deallocation
probably won't work).

If the host machine and OS are 64-bit then you need a multiarch compiler
(supporting 32-bit code as the target) but you do not need multilib.

-- 
Ludovic Brenta.