Re: How to get libb to export liba's symbols?

* Neal H. Walfield:

> Hi Florian,
>
> On Tue, 10 May 2022 12:04:52 +0200,
> Florian Weimer wrote:
>> * Neal H. Walfield:
>> 
>> > There are two major constraints.  Because rpm's OpenPGP API is public,
>> > it must be preserved until the next soname bump.  And, the OpenPGP
>> > backend should be pluggable.
>> 
>> How is this plug-in mechanism supposed to work?  Via RPM configuration
>> files?
>
> It is a build-time configuration option.  When you configure rpm, you
> can do:
>
>   ./configure --with-crypto=sequoia
>
> to get the Sequoia backend.  --with-crypto defaults to libgcrypt,
> which uses the internal OpenPGP implementation with libgcrypt.  (There
> is also --with-crypto=openssl, which uses the internal OpenPGP
> implementation with OpenSSL.)

That's a very limited form of pluggability.

I expect the most portable approach (for ELF targets) is to use a stub
shared object that contains all symbols, including those provided by
dependencies.  (librpmio.so should probably be a linker script
referencing the actual object, to prevent accidental loading of
librpmio.so via dlopen.)  That approach keeps the run-time DT_NEEDED
value an implementation detail.

I don't know if libtool supports that out of the box.

On non-ELF targets, you may need forwarder functions, and the plug-in
library cannot use the same symbols.

Thanks,
Florian