Re: changing build dependencies in a distribution from g77 to gfortran

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

>>>> Some months ago, the GCC/gfortran developers asked distributors to still
>>>> ship g77 in their next release of a distribution.  Looking forward at
>>>> the Debian etch release on the horizon and at upcoming Ubuntu releases,
>>>> I had a first look at making g77 the secondary choice as a f77 compiler,
>>>> or removing it from the release altogether and using gfortran as the
>>>> preferred f77 compiler.
>>>
>>> IMHO as of gcc 4.2, or perhaps even 4.1, gfortran is stable enough to be
>>> generally usable as the system Fortran compiler. Of course, if you want
>>> 100% bug-for-bug compatibility with g77, then g77 is your only option.
> 
> Currently Debian ships gcc 4.2 only in "experimental", although 4.1 will
> be in our upcoming "Etch" release.  But then we certainly won't have
> time to switch to gfortran before the Etch release anyway.
> 

4.1,x is probably stable enough for a f77 compiler, but if you could
use the gfortran in 4.2 you'll run into fewer potential problems.  

>>> And just to make your life even more miserable, there will be ABI
>>> breakage in libgfortran in the not too far future. IIRC 4.2 bumped the
>>> so version from 4.1, and it will probably happen again for 4.3.
>>> Hopefully we'll get symbol versioning for 4.3 and thus get some
>>> semblance of ABI stability, courtesy of yours truly, but the patch has
>>> stalled due to some minor problems and I'm quite busy with Real Life(TM)
>>> at the moment so I haven't had time to look into it.  :(
> 
> What is the expected timeframe for 4.3 to be released?

I don't think anyone has any idea when 4.3 will be released.  Heck, 4.2.0
hasn't yet been released, and there was recent discussion on skipping
4.2 completely.

> If it is well before the expected release of Debian "Lenny", then
> probably it would make sense for us to hold off on a g77 -> gfortran
> transition until after 4.3.  (Or do the gfortran folks expect further
> ABI breakage even after 4.3?)

I don't use Debian.  I don't use linux.  But, I think you do not want
to wait and continue to use g77.  g77 is unsupportedi by GCC.

> Let me ask another vaguely related question too, although I'm aware you
> guys may not be the best audience to answer it.  Do you happen to know
> whether/how the ABI of "g95" differs from that of gfortran?  Would
> people using g95 need their own set of Fortran-using libraries built
> specifically with that compiler?  Just wondering, since there has been
> occasional interest expressed in also getting g95 packaged for Debian.

g95 uses the gcc-4.0.0 middle and back-end, and it has it's own runtime
library.  You probably cannot and do not want to mix gfortran and g95.
You'll also want to check the Polyhedron Benchmark (google it).  gfortran
produces much faster executable in comparison to g95.

-- 
Steve