Re: Removing link-time cross-module refs in contrib

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2016-10-03 12:29:18 -0400, Tom Lane wrote:
>> The patch seems pretty successful in terms of being noninvasive to
>> the code. I think the major objection to it would be that we no
>> longer have any direct compiler-verified connection between the
>> signatures of the called functions in hstore/plpython and what
>> hstore_plpython thinks they are.

> We could instead add a AssertVariableIsOfType(), besides the library
> lookup maybe?

Hmm ... had not occurred to me that that might work on a function name.
I'll go try it.

>> If we were to push forward with this idea, the remaining work
>> would be to fix the other two contrib transform modules similarly,
>> after which I would want to revert the changes in commit cac765820
>> and later that suppressed linker errors for unresolved symbols in
>> contrib links. The possibility of getting back that error detection
>> is actually the main motivation for this IMO.

> That'd be rather neat.

I experimented with that aspect a bit today. For macOS it's sufficient
to remove the "-Wl,-undefined,dynamic_lookup" linker flag that cac765820
added. However, ignoring unresolved symbols in shlibs is the default
on Linux, and while you can make it throw errors, that just leads to
errors for all the references into the core backend. Not very helpful.
AFAICS, GNU ld lacks any equivalent to macOS' -bundle_loader switch,
which is what we'd need to make this usable.

A workable compromise for Linux might be to enable -Wl,-z,now which
changes unresolved symbol resolution from lazy to on-load. That would
at least guarantee that any testing whatsoever would detect incorrect
references, even if the bad call wasn't exercised.

No idea about what to do to change this on Windows. If we had error
detection on Linux+Windows+macOS that would be good enough for me ---
anyone who feels like fixing it for minor platforms is welcome to,
but it would be unlikely that we'd detect any new problems.

regards, tom lane