When postgres 9.3 was installed by apt, it doesn't work.

[8398a7]

/usr/bin/ld: /opt/crystal/bin/../embedded/lib/../lib/libgc.a(os_dep.o): undefined reference to symbol '_end'
//lib/x86_64-linux-gnu/libcom_err.so.2: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

require "pg"
DB = PG.connect("postgres://user@localhost:5432/db")
result = DB.exec({Int32}, "select count(id) from users")
p result

• ubuntu 14.04LTS
• postgres 9.3.9
• crystal 0.7.5

I want to know how to resolve this issue.

[will]

This looks similar to #8 which is some sort of linking problem that we weren't able to get to the bottom of, unfortunately.

Just to make sure when you run pg_config all the values there are correct?

[8398a7]

I tried some pg_config value, but there were not correct.

It ran correctly after to 9.4 the postgres.
Despite pass the test with postgres 9.3 in travis, I wonder.

[will]

The version of the server doesn't matter much as long as it's > 7.3 or so, the last time the protocol changed.

What I think happened is there was something not quite right with your local postgres setup, if pg_config was giving the wrong information, and when you updated to 9.4 you fixed that as a side-effect.

This project uses pg_config to find the appropriate directories to link against.

[8398a7]

I investigated the pg_config, there was a difference such as follows.

# postgres 9.3.9
INCLUDEDIR = /usr/include/postgresql
LIBDIR = /usr/lib

# postgres 9.4.4
INCLUDEDIR = /usr/include/postgresql
LIBDIR = /usr/lib/x86_64-linux-gnu

Therefore, I tried to rewrite the libpq.cr in this way with postgres 9.3.9, it was successful.

module PG
  @[Link(ldflags: "-lpq -I`pg_config --includedir` -L /usr/lib/x86_64-linux-gnu")]
  lib LibPQ

My postgres was installed by apt, therefore what is better to take action as good think.
What do you think?

[will]

Did/do you have the libpq-dev package installed from apt?

[8398a7]

Yes, I have.

[ysbaddaden]

I'm having this bug too, on a "clean" ubuntu trusty install. I never upgraded from another release and I only ever installed PostgreSQL 9.3 (but am up to date on updates and security).

The minimum snippet to reproduce is:

require "pg"
PG.connect("postgres://postgres:@localhost/")

• it fails to compile with the official crystal DEB packages, which uses some embedded static libs (eg: libpcl.a, libgc.a, ...)
• it passes if I compiled crystal myself, which uses shared libraries (so static libs may be a hint)
• it passes with crystal test_pg.cr --link-flags "-L/usr/lib/x86_64-linux-gnu" (something seems required in that directory)

BTW: the -I includedir is unnecessary in the @Link definition since crystal doesn't care about headers files. Actually @[Link("pq")] is enough on Linux, except that we need the -L/usr/lib/x86_64-linux-gnu, even though libpq is installed in /usr/lib. Maybe libpq merely highlights a linking issue that is unrelated?

[ysbaddaden]

Errata: it passes with -L/usr/lib/x86_64-linux-gnu because the linker no longer uses the embedded static libs from /opt/crystal/embedded/lib and instead uses shared libs from /usr/lib/x86_64-linux-gnu to compile the binary.

[ysbaddaden]

Related (unsolved): http://stackoverflow.com/questions/13328144/end-symbol-disappears-when-linking-to-libcurl

[will]

Is /usr/lib/x86_64-linux-gnu not the result of pg_config --libdir for you?

If it is the same, then I don't understand why the @[Link(ldflags: "-lpq -Ipg_config --includedir-Lpg_config --libdir")] line doesn't work (even if -I isn't necessary).

If it isn't the same, then I don't understand why your pg_config is returning incorrect data.

[ysbaddaden]

No, pg_config --libdir states /usr/lib which is where libpq.{a,so} is indeed installed.

This seems to be a common linker bug, triggered by linking against libgc.a and libpq.so or libcom_err.so but doesn't happen when using libgc.so (or something like that).

[will]

I checked with my Ubuntu-using colleges, and they have pg_config binaires that give the correct results

~$ pg_config --libdir
/usr/lib/x86_64-linux-gnu

Can you try something like

export PATH=/opt/PostgreSQL/9.3/bin/:$PATH

(or wherever the binaries are) to get a proper pg_config?

[fdr]

Hi,

@will asked me to have a look at how pg_config presents --libdir on Ubuntu. It looks like it has a useful value on my system:

$ pg_config --libdir
/usr/lib/x86_64-linux-gnu
$ cat /etc/issue.net 
Ubuntu 15.04

[fdr]

I use the PGDG packages.

[will]

@fdr I've been able to reproduce this on an aws instance, and it also happens on the image b&p uses for slugc. I added your pubkey to the aws instance, can you help me track this down?

[will]

So, @fdr and I tracked this down more, crystal-lang/crystal#1269

It explains why when the libdir isn't /usr/lib things work

[will]

The driver is now native, so this problem is no longer relevant.