Re: Switching the default for -fabi-version

[Michael Matz <matz at suse dot de>]

Hi,

On Tue, 21 Oct 2003, Joe Buck wrote:

> No objection, though I am still curious as to whether this actually makes
> a difference for any actual, widely used source code out there

Okay someone tested KDE/Qt with -Wabi, and it spits about 300-500 warnings
per compilation unit (!).  A common one is about implicit virtual dtors
or something, because we have code in structure like:
   class Base { virtual ~Base() {} };
   class Derived: public Base { ... no ~Derived(); };

And each qpixmap gives an empty class warning:
 "contains empty classes which may cause base classes to be placed at
  different locations in a future version of GCC"

A thing stressing C++ quite a bit is aRts, which additionally often gives:
 "virtual base is not ABI-compliant and may change in a future version of
  GCC."

> (that is, does -Wabi report anything for real programs that aren't
> specially constructed to tweak ABI bugs?  How often?)

So, definitely yes.  I doubt though, that it matters, because we also link
against libstdc++ (of course), and hence the new compiler anyway means
full recompilation and lost of backward compatibility.  I hope that
somewhen this all becomes better, like with glibc ;-)


Ciao,
Michael.