[Tcl-bugs] [ tcl-Bugs-3397938 ] load failes due to RTLD_LOCAL

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Bugs item #3397938, was opened at 2011-08-25 06:24
Message generated for change (Comment added) made by dgp
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Category: 17. Commands I-L
Group: obsolete: 8.6b1.1
>Status: Open
>Resolution: None
Priority: 5
Private: No
Submitted By: Ulrich Ring (uring)
Assigned to: Jan Nijtmans (nijtmans)
Summary: load failes due to RTLD_LOCAL

Initial Comment:

after switching from tcl8.6b1 to tcl8.6b2 many of our apps are failing at startup when loading
extensions, for example:

> tclsh8.6
% load ./libfoo.so
% load ./libbar.so
...error: symbol lookup error: undefined symbol: .....

this happens, because (a) libbar references a symbol which is defined in libfoo and (b) because dlopen() in tclLoadDl.c passes the
flag RTLD_LOCAL (instead of RTLD_GLOBAL).

this seems to be a known problem, discussed for example in bug #3216070.

I understand the reasons why you came up with this change. But from a rather naive point of view
it causes a severe incompatibility, stopping the many apps here which are built upon the above
mentioned dependencies.

At present I see the following options:

(a) hacking tclLoadDl.c back to using RTDL_GLOBAL;
     not an approach I were happy with. Instead I'd prefer
    a compile option like -DLOAD_GLOBAL.
(b) getting an option "-global" in tcl8.6b3, though this
   needs changing  all "load .. " commands.
(c) changing the link of libbar.so introducing  an
    implicit depenency "-lfoo". don't know how 
   portable this advice ist. here (linux, SuSE 11.4,
   binutils-2.21-13.1.x86_64) it seems to work.

What do you suggest to get around this load-failures?



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>Comment By: Don Porter (dgp)
Date: 2011-08-26 11:41

Message:
Re-opened.  At the least, this points out that
I failed to flag this incompatibility in the release notes,
and will want to do better on that for 8.6.0.  As I
mentioned on TCLCORE regarding plans for 8.6b3
and beyond, I want to see documents take shape
to help the Tcl user migrating to 8.6 on how they
can take advantage of the changes in it.  Do we
have such guidance for this issue?  If so, where
is it?

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Comment By: Alexandre Ferrieux (ferrieux)
Date: 2011-08-25 11:26

Message:
What's the place to look for documentation of such ABI breakage ?

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Comment By: Jan Nijtmans (nijtmans)
Date: 2011-08-25 06:54

Message:
Well, the Issue tracker is not meant to ask questions, but
anyway here is the anwer:

(c) is the 'right' solution, and it works on all systems
using ELF. If you want to make it portable, use TEA
to build your libbar.so, then SHLIB_LD_LIBS is
set to ${LIBS} for most systems and empty
for systems that don't support it.

Hope this helps,
          Jan Nijtmans

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