[gnutls-devel] symbol and library versioning

[Nikos Mavrogiannopoulos]

On Fri, Aug 11, 2017 at 11:46 AM, Andreas Metzler <ametzler at bebt.de> wrote:
> On 2017-08-11 Nikos Mavrogiannopoulos <n.mavrogiannopoulos at gmail.com> wrote:
>> On Thu, 2017-08-10 at 14:21 +0200, Andreas Metzler wrote:
> [...]
>>>> As such for every symbol introduced on a particular version, we
>>>> create an entry in libgnutls.map based on the version and containing
>>>> the new symbols. For example, if in version 3.6.3 we introduce
>>>> symbol gnutls_xyz, the entry would be:
>
>>>> GNUTLS_3_6_2 { global: gnutls_xyz; } GNUTLS_3_6_1;
>
>>>> where GNUTLS_3_6_1 is the last version that symbols were introduced,
>>>> and indicates a dependency of 3.6.2 to symbols of 3.6.1.
>
>>> This has not been a problem with the old approach.
>
>> Do you refer to the text above or the backporting issue?
>
> Hello,
> I was refering to the backporting issue ("Backporting new symbols to an
> old version which is soname compatible is not allowed"). e.g.
> gnutls_pkcs7_get_embedded_data_oid() was backported to 3.4.17 from
> 3.5.6.
>
> Afaiui this would be forbidden/impossible now.  If 3.4.17 exported
> gnutls_pkcs7_get_embedded_data_oid at GNUTLS3_4_17 then 3.4.17 and 3.5.6.
> would have been ABI incompatible, an upgrade from 3.4.x to 3.5.x would
> require a rebuild of all binaries using
> gnutls_pkcs7_get_embedded_data_oid.

Right. That's why it is now forbidden. A work around this could be for
later 3.5.x versions to link the old symbol to the new one, though
that is still a work around, as it still has some rough points (some
3.5.x releases would still be abi incompatible).

> I am not sure about the problems caused by doing it the other way round
> (3.4.17 exporting gnutls_pkcs7_get_embedded_data_oid at GNUTLS3_5_6) but I
> guess rpm's dependency tracking might stumble. - Or would the
> differently chained version definitions (GNUTLS3_5_6 depending on
> GNUTLS3_4_8 or GNUTLS3_5_5 respectively) break the ABI?

My understanding is that the chaining has no effect on rpm tracking,
nor affect the ABI. However as you mention above that method will
break its dependency tracking.

regards,
Nikos