Re: [TCLCORE] [Tcl-bugs] [ tcl-Bugs-3216070 ] Loading extension libraries from embedded Tcl applications

[Jan N. <jan...@gm...>]

Hi, tcl-core members,

I would like to start a discussion about [tcl-Bugs-3216070]. As I
already described in:
<https://sourceforge.net/tracker/index.php?func=detail&aid=1961211&group_id=10894&atid=110894>
the RTLD_GLOBAL flag is dangerous. This is the first report
I see related to Tcl describing this, even though it still is not
fully understood what's happening here. Outside of Tcl, there
are more examples, e.g.:
<http://www.mail-archive.com/tnt...@li.../msg00168.html>

My proposal would be to change the flag to RTLD_LOCAL, but
there are situation where that would break:
- [Tcl bug #1961211] would be re-introduced.
- On platforms where SHLIB_LD_LIBS="", we will lose the
  dynamic loadability of libtk. Currently those platforms are:
       dgux*
       MP-RAS-*
       OSF1-1.*
       QNX-6*
       SCO_SV-3.2*
       SINIX*5.4*
       SunOS-4*
       UNIX_SV* | UnixWare-5*
  Most of them are removed now from TEA,
  the only two remaining are:
       QNX-6*
       SCO_SV-3.2*
  (I don't even know if dynamical loading of libtk
  works on those platforms anyway......)
  Two questions arise:
  - Do we still care about those 2 platforms?
  - If we do, could we make a change to:
        SHLIB_LD_LIBS='${LIBS}'
    maybe that just works, I don't think anyone
    tried that yet. Anyone????

Before we make this change, first there should
be a clear view about what would break
practically. If too much would break, I see
two alternatives:
- Let RTLD_LOCAL be the default, but provide
  a new option to load libraries using RTLD_GLOBAL
- Only make the change in Tcl8.6, and flag it
  with *POTENTIAL INCOMPATIBILITY*

Any other ideas?

Regards,
           Jan Nijtmans
2011/3/16 SourceForge.net <no...@so...>:
> Bugs item #3216070, was opened at 2011-03-16 12:37
> Message generated for change (Tracker Item Submitted) made by mxmanghi
> You can respond by visiting:
> https://sourceforge.net/tracker/?func=detail&atid=110894&aid=3216070&group_id=10894
>
> Please note that this message will contain a full copy of the comment thread,
> including the initial issue submission, for this request,
> not just the latest update.
> Category: 40. Dynamic Loading
> Group: current: 8.5.9
> Status: Open
> Resolution: None
> Priority: 5
> Private: No
> Submitted By: Massimo Manghi (mxmanghi)
> Assigned to: Kevin B KENNY (kennykb)
> Summary: Loading extension libraries from embedded Tcl applications
>
> Initial Comment:
> Shared libraries providing Tcl extensions are loaded for the Unix family by the code in tclLoadDl.c, which interfaces Tcl with the dlopen(<library_path>,flags) system call. Tcl chose to set dlopen's flags argument as RTLD_NOW | RTDL_GLOBAL. Globally loading the extension symbols  was found to crash an application (Apache Rivet) that embeds a Tcl interpreter, which in turn gains access to a subset of the application commands by loading an extension library. The application successfully loads the library by calling Tcl_PkgRequire, but crashes shortly after in a function unrelated to the extension library. Replacing Tcl_PkgRequire with a direct call to dlopen and passing RTLD_NOW | RTLD_LOCAL as second argument restores mod_rivet (and Apache) full functionality. On the other hand, it was also verified that setting in tclLoadDl.c the flags argument as RTLD_NOW | RTLD_LOCAL  and building a custom Tcl installation against which Rivet gets linked, preserves Apache functioning even when the extension is loaded by calling Tcl_PkgRequire, thus fully identifying the problem with the RTLD_GLOBAL flag.
>
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> https://sourceforge.net/tracker/?func=detail&atid=110894&aid=3216070&group_id=10894
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