GCC mailing list dit :
Hi Sameer Sinha,

> can any one tell me what is the difference between gcc-ada and
> differnt other compiler for Ada 95 like GNAT GPL, GNAT Pro, ????
> what is procedure to build only language Ada by using source code og gcc-4.1???

they are closely related. There are two groups:
(1) versions released by ACT (http://www.gnat.com): GNAT GPL and GNAT Pro.
(2) versions released by the FSF (http://gcc.gnu.org): gcc-4.1 etc

GNAT Pro is ACT's commercial offering: you have to have a support contract
with them to get it. GNAT GPL is basically the same compiler, but it is
unsupported, and the license has been changed so that software built with
and distributed to the world has to be under the GPL license to be legal
(at least, that seems to be the intention).

The FSF compiler is freely available and doesn't have the license restrictions
of the GNAT GPL.

The technical differences between the compilers are basically in the code
generators: the ACT compilers use a modified code generator from gcc 3.4.6.
The FSF compilers use more recent and quite different code generators.
However the ACT compilers tend to be more stable than the FSF ones, because
the FSF code generators and the Ada front-end do not yet interact perfectly.

I understand that the next releases of GNAT GPL and GNAT Pro will be based
on the same code generator as the FSF compilers, at which point the difference
between the FSF and ACT offerings will doubtless be much less.

Best wishes,

Duncan.