bonzini at gnu.org
Fri Jan 8 18:11:39 CET 2010
On 01/08/2010 05:33 PM, Torbjorn Granlund wrote:
> Paolo Bonzini<bonzini at gnu.org> writes:
> I also noticed that GMP 5 is using an interface "age" of 6. This is
> wrong since interface 9 is not backwards compatible with interface
> 8. The fact that mpn_bdivmod was documented as mutable does not
> matter: distributions will want to provide libgmp.so.3 and libgmp.so.9
> for a while, and this is not possible if GMP 5 says it is binary
> compatible with 4.3.2.
> I suggest that the attached patch is applied before distributions
> start to complain.
> We consider mpn_bdivmod is not part of the official API of any GMP
> release. Therefore, we did not zero age. This was a deliberate
It doesn't matter, for various reasons:
1) Since you are not hiding symbols using things such as libtool's
--export-symbols or ELF visibilities, libgmp.so exports all internal
functions. So, one could say that the ABI includes all the internal
functions and that AGE should be zeroed even if you remove an internal
To avoid similar pitfalls, I suggest that you start using
--export-symbols or ELF visibilities to hide symbols that you do not
want to publish (and zero the age in the process).
2) you made a conscious decision to break the API, and that's fine---I
have no problem with programs that do not compile anymore because they
used mpn_bdivmod, they should have expected it. However, the age field
is about not breaking the ABI, and this is a more mechanical fact. Your
decision not to reset the age means that there is no way to keep
existing programs that use mpn_bdivmod while installing new programs
that will use new interfaces introduced in GMP 5. Another way to say
this is, "installing GMP 5 may break existing binaries on the system, so
the age should be reset".
3) the function was while documented to change in the future, however it
was also documented to be there for now. I think that you are setting
too high a price for having used an unstable but documented interface.
Maybe the mistake was to document mpn_bdivmod in the first place, but
now you have to live with it.
4) distributions _will_ notice the problem since they have automated
tools to detect ABI breakage. They may decide to waive it, or they
could fix the problem by resetting the age themselves or by adding back
mpn_bdivmod. In any case, it's best to fix the problem upstream.
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