Re: pgsql: Build src/port files as a library with -fPIC, and use that in li

Christoph Berg <myon(at)debian(dot)org> writes:
> Re: Tom Lane 2018-09-28 <20671(dot)1538142538(at)sss(dot)pgh(dot)pa(dot)us>
>> I proposed in
>> https://www.postgresql.org/message-id/19581.1538077716@sss.pgh.pa.us
>> that we should remove pqsignal, as well as
>> pg_utf_mblen
>> pg_encoding_to_char
>> pg_char_to_encoding
>> pg_valid_server_encoding
>> pg_valid_server_encoding_id
>>
>> from libpq's exports, on the grounds that (a) nobody should be using
>> those (they're undocumented as exports), and (b) anybody who is using
>> them should get them from libpgport/libpgcommon instead. Thoughts?

> It took a while to notice, but this change does break 8.2's initdb if
> libpq5 from PG12 is installed:
> $ /usr/lib/postgresql/8.2/bin/initdb
> /usr/lib/postgresql/8.2/bin/initdb: symbol lookup error: /usr/lib/postgresql/8.2/bin/initdb: undefined symbol: pqsignal

Well, 8.2 is *very* long out of support, and there are plenty of
nasty bugs you're at risk of if you keep using it. So I don't
find this to be a good argument for contorting what we do in v12.

If you really want to keep using 8.2 (and even make new installations
with it!?), you could back-patch the 8.3 patch that made sure that
initdb didn't absorb pqsignal, pg_encoding_to_char, etc from libpq.
It looks like what you'd need is a portion of the Makefile changes
from 8468146b03c87f86162cee62e0de25f6e2d24b56.

BTW, I noticed this in that patch's commit message:

Going forward, we want to fix things so that encoding IDs can be changed
without an ABI break, and this commit includes the changes needed to allow
libpq's encoding IDs to be treated as fully independent of the backend's.
The main issue is that libpq clients should not include pg_wchar.h or
otherwise assume they know the specific values of libpq's encoding IDs,
since they might encounter version skew between pg_wchar.h and the libpq.so
they are using. To fix, have libpq officially export functions needed for
encoding name<=>ID conversion and validity checking; it was doing this
anyway unofficially.

So it was wrong of me to propose moving pg_encoding_to_char() et al
into libpgcommon: doing so would've re-introduced the hazard of
client code misinterpreting the encoding IDs returned by
PQclientEncoding() (and how the heck did I miss that libpq.sgml
does document that function for exactly that purpose?).

Fortunately, I didn't do that ...

regards, tom lane