Re: Gnat Free ?

[dewar@gnat.com]

In article <Pine.BSF.4.05.9810181759320.11365-100000@shell5.ba.best.com>,
  Brian Rogoff <bpr@shell5.ba.best.com> wrote:

> What I meant was to install your version of GNAT in such a way that it
> does not interfere with whatever version of gcc you are using to do "real"
> work. When I was in graduate school, I didn't have the option of installing
> GNAT in the normal place, so I had to install it under my home directory
> and rely on a little shell hackery to make it easier to use both
> gcc-<whatever>, which was our main development tool, and GNAT, which I was
> using just to learn Ada. I believe that the configure script for that
> ancient version of GNAT supported this option directly. This is the brute
> force approach to coexistence, maintaining two entirely separate
> compilers, but it worked for learning.


This approach actually works quite well for production use if you set things
up properly.

One of the problems with gcc at the moment is that there are
multiple source bases (e.g. Apple (Rhapsody), Wind River (VxWorks),
Softway Systems (Interix), Cygnus (EGCS)) all differ significantly from
the FSF GCC version that is used by GNAT.

There is no easy way to distribute GNAT in a manner that is intimately
compatible with other compilers using all these possible source bases, so
indeed the safest thing if you are using other gcc compilers with a different
source base is to install an entirely separate version of GNAT.

Note that all GCC patches developed for GNAT are immediately incorporated
into the FSF GCC sources (e.g. GCC 2.8 contains all the GCC 2.7 patches
developed for GNAT, and the snapshots contain the patches as they are
developed). This is why for example people have been successfully able
to build GNAT with EGCS (though that requires some additional patches,
since EGCS has developed some incompatible interfaces from GCC), since
EGCS generally picks up the FSF GCC patches.

It is definitely the case that using the binary version of GNAT as distributed
by us is the least likely to get you into to trouble. It does require some
shell script work to integrate with other gcc compilers around, but this
is straightforward, and several of our customers have adopted this approach
successfully.

Incidentally, one thing that is not possible for us is to distribute updated
versions of the gcc patch file that work with a current public release, and
some newer or different version of gcc. That is because we simply don't
develop such files. Once a version of GNAT is released, we maintain it at
the same GCC base level for its entire life time.

Developing such patch files is certainly useful, and if the volunteer
community can do this, as for example they have for GNAT 3.10p + EGCS, this
is certainly most welcome by the user community of the public version. We are
happy to arrange for posting of any such patch files in the contrib
directories at NYU. Note that we don't control this site, but they will put
up anything we give them! Note also in developing such patch files that, as I
mentioned above, the GNAT patches do appear in the GCC source snap shots.

I would suggest that future more detailed discussion of this issue might
better be done on chat@gnat.com where many serious GNAT users participate
who do not have time to participate in comp.lang.ada.

Robert Dewar
Ada Core Technologies

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