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Re: FreeBSD 5.3: Sharedlibs using sharedlibs (and Tcl)

From: Palle Girgensohn <girgen(at)FreeBSD(dot)org>
To: Peter Much <pmc(at)citylink(dot)dinoex(dot)sub(dot)org>
Cc: freebsd-questions(at)freebsd(dot)org, freebsd-ports(at)freebsd(dot)org,freebsd-hackers(at)freebsd(dot)org, brett_schwarz(at)yahoo(dot)com,pgsql-interfaces(at)postgresql(dot)org
Subject: Re: FreeBSD 5.3: Sharedlibs using sharedlibs (and Tcl)
Date: 2005-03-24 23:56:35
Message-ID: DC6885CCF9A98F416ED9E7FC@palle.girgensohn.se (view raw or flat)
Thread:
Lists: pgsql-interfaces
--On onsdag, mars 16, 2005 20.13.03 +0100 Peter Much 
<pmc(at)citylink(dot)dinoex(dot)sub(dot)org> wrote:

> On Wed, Mar 16, 2005 at 03:35:16PM +0100, Palle Girgensohn wrote:
> !
> ! --On onsdag, mars 16, 2005 11.43.31 +0100 Peter Much
> ! <pmc(at)citylink(dot)dinoex(dot)sub(dot)org> wrote:
> !
> ! >! So, you're saying that pctclsh *can* access, but pgaccess *cannot*?
> ! >Odd...  ! I would expect they'd both use the same lib to connect, no?
> ! >I'll have to
> ! >
> ! >They use the same libraries, yes. But Tcl interpreter seem to need more
> ! >advice on where to find sub-functions in other libraries. It looks
> ! >like this:
> ! >
> ! >pgtclsh  -finds-> libpgtcl.so -finds-> libpq.so -finds-> libkrb5.so
> ! >pgaccess -loads-> libpgtcl.so -finds-> libpq.so -fails-> libkrb5.so
> !
> ! Uh, OK. I'm not qualified enough with linkers to answer this, I'm
> afraid.  ! Did you try the pgsql-interfaces mailing list?
>
> Oh well, same with me. I sent a copy of one of my reports to that
> list, yes. But only got feedback that it will be evaluated by
> moderator, as I am not signed on that list.
> I'm actually no professional psql user - the database is just a small
> part of my installation, mainly logging the lowlevel error counts
> from my exabyte drives and providing reports about tape wearout.
> And the kerberos is just there for fun, as a reference installation.
>
> Nevertheless, I would think this is not a matter for the postgres
> community. Because this would happen the same way with any other
> application that provides Tcl support and kerberos support (or maybe
> also with other components of the system, if they are used from Tcl).
>
> So it seems either a Tcl problem or a linker/loader problem. Which,
> I cannot say - maybe both.
>
> ! >And then I found that it is enough to place into libpq.so the explicit
> ! >references to libkrb5 and the other kerberos libs. That is what the
> ! >"readelf -a" output in my other mail shows.
> !
> ! sounds like a better solution, yes... Shouldn't they always be there?
> ! Sounds like a bug to me?
>
> Thats the question.
> I just did a little more investigation (like reading manpages)
> and found out _WHY_ it does work for pgtclsh but not for pgaccess.
>
> There is a command "ldd" that shows nested library dependencies
> for any program.
> For pgtclsh it shows all the kerberos libs:
>
> bash-3.00# ldd /usr/local/bin/pgtclsh
> /usr/local/bin/pgtclsh:
>         libpgtcl.so.2 => /usr/local/lib/libpgtcl.so.2 (0x28075000)
>         libpq.so.3 => /usr/local/lib/libpq.so.3 (0x2807d000)
>         libtcl84.so.1 => /usr/local/lib/libtcl84.so.1 (0x28097000)
>         libm.so.3 => /lib/libm.so.3 (0x28135000)
>         libkrb5.so.7 => /usr/lib/libkrb5.so.7 (0x2814f000)
>         libasn1.so.7 => /usr/lib/libasn1.so.7 (0x28186000)
>         libcrypto.so.3 => /lib/libcrypto.so.3 (0x281a6000)
>         libroken.so.7 => /usr/lib/libroken.so.7 (0x2829b000)
>         libcrypt.so.2 => /lib/libcrypt.so.2 (0x282a9000)
>         libcom_err.so.2 => /usr/lib/libcom_err.so.2 (0x282c1000)
>         libz.so.2 => /lib/libz.so.2 (0x282c3000)
>         libreadline.so.5 => /lib/libreadline.so.5 (0x282d3000)
>         libutil.so.4 => /lib/libutil.so.4 (0x282ff000)
>         libc.so.5 => /lib/libc.so.5 (0x2830b000)
>         libintl.so.6 => /usr/local/lib/libintl.so.6 (0x283e4000)
>         libssl.so.3 => /usr/lib/libssl.so.3 (0x283ed000)
>         libncurses.so.5 => /lib/libncurses.so.5 (0x2841b000)
>         libiconv.so.3 => /usr/local/lib/libiconv.so.3 (0x2845a000)
>
> But for libpgtcl.so (this is the first elf binary that pgaccess gets
> to see) it does not show these kerberos libraries (I use the old
> libpq.so here, not the one that I have modified):
>
> bash-3.00# ldd /usr/local/lib/libpgtcl.so
> /usr/local/lib/libpgtcl.so:
>         libpq.so.3 => /usr/local/lib/libpq.so.3 (0x2815a000)
>         libtcl84.so.1 => /usr/local/lib/libtcl84.so.1 (0x28174000)
>         libm.so.3 => /lib/libm.so.3 (0x28212000)
>         libintl.so.6 => /usr/local/lib/libintl.so.6 (0x2822c000)
>         libssl.so.3 => /usr/lib/libssl.so.3 (0x28235000)
>         libcrypto.so.3 => /lib/libcrypto.so.3 (0x28263000)
>         libiconv.so.3 => /usr/local/lib/libiconv.so.3 (0x28358000)
>
> Then the explanation became simple: these kerberos libraries get
> just LITERALLY LISTED WITHIN THE pgtclsh BINARY! And this is an
> impossible method for a Tcl script.
>
> bash-3.00# readelf -d /usr/local/bin/pgtclsh | grep krb5
>  0x00000001 (NEEDED) Shared library: [libkrb5.so.7]
>
> So now we have a full explanation for the behaviour, but not really
> a solution.
> Instead, this looks like a fundamental question about how to load
> nested elf sharedlibs from interpreter languages.
>
> From my technical viewpoint, the only solution that makes sense
> would be: every shared library must reference all other shared
> libraries from which it uses functions. The shared library cannot
> rely on the executable to do this job, because the executable
> may be an interpreter script, which neither is able to do this
> nor would it want to know them all.
>
> From this viewpoint, the linker command that creates libpq.so
> is defective. So You were right and its a problem for the
> postgresql developers.
>
> But as I am not competent with shared libraries and development
> systems and such stuff, I would very much appreciate the opinion
> of somebody with profound knowledge of these things. And anyway,
> perl should have similar problems.
>
> Ok, lets see - which nice mailinglists do we crosspost today?
> I go with questions and ports, and add hackers. I think we're now
> deep enough in the rabbithole for them. ;-)
> And psql-interfaces.
>
> PMc


Hi!

Has anyone been able to shed any light on this? postgres + kerberos makes 
libpqxx and libpqtcl fail, at least on FreeBSD. Any ideas?

/Palle


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