Re: Reduce function call costs on ELF platforms

Andres Freund <andres@anarazel.de> writes:
> Basically they way we currently build our extensions, the compiler & linker
> assume every symbol inside the extension libraries needs to be interceptable
> by the main binary. Which means that all function calls to symbols visible
> outside the current translation unit need to be made indirectly via the PLT.

Yeah, that would be nice to improve.

> The easier approach for this class of issues is to use the linker option
> -Bsymbolic.

I don't recall details, but we've previously rejected the idea of
trying to use -Bsymbolic widely; apparently it has undesirable
side-effects on some platforms.  See commit message for e3d77ea6b
(hopefully there's some detail in the email thread [1]).  It sounds
like you're not actually proposing that, but I thought it would be
a good idea to note the hazard here.

> By compiling with -fno-plt, the above becomes:

Does -fno-plt amount to an ABI change?  If so, I'm worried that it'd
break the ability to compile extensions with a different compiler.

Also, we have at least some places where there actually are cross-calls
between extensions, eg hstore_perl -> plperl.  Do we need to worry about
breaking those?

            regards, tom lane

[1] https://www.postgresql.org/message-id/flat/153626613985.23143.4743626885618266803%40wrigleys.postgresql.org