svn commit: r233391 - head/contrib/libstdc++/libsupc++

[Konstantin Belousov]

On Fri, Mar 23, 2012 at 04:49:22PM -0400, Alexander Kabaev wrote:
> On Fri, 23 Mar 2012 22:23:35 +0200
> Konstantin Belousov <kostikbel at gmail.com> wrote:
> 
> > On Fri, Mar 23, 2012 at 08:10:56PM +0000, David Chisnall wrote:
> > > Author: theraven
> > > Date: Fri Mar 23 20:10:56 2012
> > > New Revision: 233391
> > > URL: http://svn.freebsd.org/changeset/base/233391
> > > 
> > > Log:
> > >   Revert ABI breakage in libsupc++.
> > >   
> > >   Unfortunately, the ABI was broken upstream for the 4.2 release,
> > > which we imported.  We then shipped the broken version for several
> > > years and certain ports (e.g. libobjc2) depend on it, so we're
> > > stuck with it for now... 
> > >   We should revisit this for 10.0, since we're allowed to break the
> > > ABI then, but until then we should keep the ABI we shipped with 8.x
> > > and 9.x.
> > 
> > No, you are not allowed to break ABI for symvered libraries, even
> > between major releases.
> 
> You are, if we are ditching the system library in favor on one in
> ports. Not polite, but I do not see a polite way out of this. The
> libraries from ports are effectively shipped with incompatible ABI in
> this area for about 4 years now. Luckily for us, breakage does not seem
> to be affecting great many applications, as they do not use the changed
> interface directly themselves. libobjc2 is the only known at the moment
> that is known to be affected.

The patch just committed made the base-shipped library incompatible
with the ports and manual libstdc++ builds. I think it is wiser to
not 'undo the undo', and instead start living with the upstream-approved
ABI. For symvered library, it does not make any difference if you break it
in 10.0 or 9.1.

Also, I think that consumers that depend of the ABI of std::typeinfo can
be hacked to understand the layout of vtable. I doubt that there are
many users that utilize typeinfo.
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