Re: GNAT for Debian

[Ludovic Brenta <ludovic.brenta@insalien.org>]

Preben Randhol <randhol+abuse@pvv.org> writes:

> Simon Wright wrote:
> > But you must be very careful where the gcc-lib/i686-whatever-linux
> > stuff goes -- not on top of your working standard compiler.
> 
> That is no problem:
> 
> /usr/lib/gcc-lib/i486-linux/2.8.1/
>                             ^^^^^
>                             gcc version

Yes, and since the dawn of time you can pass -b target -V version to
gcc, the compiler driver.  -b allows you to switch from "i486-linux"
to something else, and -V changes "2.8.1" into what you specify.  And
with a proper spec file, you can instruct gcc to handle Ada source
files (the spec file contains the defaults for -b and -V, and maps
source file name patterns with the various back-ends).

But passing -b and -V to the compiler is often difficult and confusing
in the context of recursive makefiles; hence gnatgcc.

> > So you need a clean way of putting the GNAT builds (especially if you
> > have more than one) in places where they can't be mistaken and will
> > never end up on your path.
> 
> You cannot have two gnat compilers at the same time. At least not as the
> standard compiler. 
> 
> > I choose /opt because if didn't seem like a bad idea; if it was, I am
> > very sorry. /usr/lib/gnat-3.15p (for example) would be a perfectly
> > good place, or /usr/local/gnat-3.15p.
> > 
> > You could easily then install gnatgcc and friends by symlinks in
> > /usr/local/bin (say).
> > 
> > The point of my gnatfe is to do effectively just that but in a way
> > that you can alter the compiler actually used by changing an
> > environment variable, which is effectively the prefix you built the
> > compiler with.

I think you made the right choice.  I, too, have a strict policy of
installing everything in /opt unless it is packaged for my
distribution (used to be Red Hat, now Debian).  I did install gnat
3.15p into /opt/gnat-3.15p and have a symlink /opt/gnat to point to
it; but instead of using wrapper scripts, I prefer to place
/opt/gnat/bin at the head of my PATH, and /opt/gnat/lib in
LD_LIBRARY_PATH, on a per-user basis or in /etc/profile.d.  This way,
the /usr partition never contains files that are not part of any
package.
 
> Sure, but it makes it harder to maintain as a package I would say.
> 
> Normal practice if you need more than one gcc is that is is named:
> 
> gcc-2.95
> gcc-3.2
> gcc-3.3
> 
> etc... and gcc symlinks to the standard. Of course one could do that
> too, but then one might get problems with gnatmake calling wrong gnatgcc
> because of bad symlinks. 

Yes.  On Debian, the package "gcc" creates the symlink.  In woody,
"gcc" is 2.95, but in sarge, "gcc" depends on "gcc-3.3" and points to
it.

> > I quite realize that if you're building a package for people to
> > install & use on the other side of the world without handholding,
> > things may look different!
> 
> Exactly

Aye.

-- 
Ludovic Brenta.