Re: ABI Compatibility (was Re: Installation woes for the average user...)

[David Chisnall]

On 20 May 2009, at 11:53, Yavor Doganov wrote:

> On Wed, May 20, 2009 at 11:24:39AM +0100, Richard Frith-Macdonald  
> wrote:
> > I think what you are describing (as the correct way to do things) is
> > what GNUstep already tries to do ... see
> > http://mediawiki.gnustep.org/index.php/GNUstep_release_policy for the
> > actual release policy details.
>
> On the contrary -- this very policy is the problem.
>
> The SONAME of a shared library should be bumped if and only if there  
> is
> ABI break, not because of publicity reasons, big API additions, or
> anything else.  You can continue to version stable releases with even
> numbers and unstable releases with odd numbers and release them in any
> order you feel apropriate; the SONAME has absolutely nothing to do  
> with
> the package version.

In fact, this link appears to directly contradict itself:

> The library (SONAME) versions is changed when the major or minor  
> version number of a release changes, but not the subminor number.


and

> The minor version number is changed (and therefore the library  
> version) when we break backward compatibility


This does not appear to be what really happens.  The minor version  
number is changed with each new release.  This causes installed  
applications to link against the old GNUstep if you leave it installed  
(or to just fail if you don't) and causes linker problems with  
frameworks, since they will link against the GNUstep that they were  
compiled against while apps that link against them will also link  
against the new GNUstep.

> > > > How you version the releases and what is considered
> > > > "stable" and "unstable" is completely orthogonal to the library
> > > > versioning.
> >
> > is technically true, it's not what people expect in practice, and
> > therefor not policy.  The policy is to keep the main so version  
> > numbers
> > in sync with the main release version numbers, because that matches
> > normal expectations.
>
> Name just one library -- just one -- on your GNU system that behaves
> this way.  Consider what would happen if glibc or glib/gtk+ bump the
> soname every six months...  I find it incredibly hard to believe that
> this is "normal expectation".

Totally agree.  For a great many packages (and for OS X frameworks)  
the soname is completely unrelated to the library version.  If you  
need to know the installed library version, you ask your package  
manager or pkg-config, or you read some global value / call some  
global function.

> > However, I don't think there have been any recent releases which  
> > should
> > have changed the so number for any of the libraries.
>
> I've made an experiment some time ago by altering the symlinks without
> recompiling anything.  Every GNUstep app in Debian worked out of the  
> box
> (of course that's not a 100% proof that the new Base/GUI were ABI
> compatible).

Exactly the same for me on FreeBSD.  We're not actually breaking the  
ABI, we just look to the linker / loader like we are doing, which is  
even worse because it has the same effect while being trivially fixable.

David