Re: Trouble with portable linking

[Florian Weimer <fw@deneb.enyo.de>]

* Ryan Burn:

> On Thu, Dec 17, 2020 at 12:14 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>
>> If you want to be compatible with glibc versions that check the
>> embedded soname in symbol versions (which is not visible in the @
>> syntax), you need to build a stub library that defines the required
>> symbol versions in the right shared object.  There is no way to
>> achieve this with .symver directives.
>
> Thanks for the response! Could you elaborate a little more on how I
> can build the stub library?

Here's a script that generates such a stub DSO from an existing full
DSO:

<https://git.centos.org/rpms/compat-glibc/blob/c7/f/SOURCES/dummylib.sh>

It is not completely correct for data symbols; that part needs a bit
of tweaking to get the alignment right.  The resulting assembler file
is architecture-specific because the object sizes and symbol versions
are.

> If I understand correctly, newer versions of glibc will resolve a
> versioned symbol even if the embedded soname doesn't match. Is there a
> way to explicitly define the soname so that I can specify it to
> libpthread?

The link editor copies the soname of the shared object that contains a
versioned symbol definition when it generates the versioned symbol
reference.  That's why I think you need that stub DSO.  It's the only
way I know of that actually works.