Re: Cannot exec() program outside of /bin if PATH is unset

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Oct 10 17:39, Corinna Vinschen wrote:
> On Oct 10 14:13, Arjen Markus wrote:
> > 2014-10-10 13:22 GMT+02:00  <tednolan>:
> > >>2014-10-10 13:24 GMT+02:00 Jan Nijtmans <...>:
> > >>> 2014-10-10 12:34 GMT+02:00 Corinna Vinschen <...>:
> > >>>> On Oct  9 11:46, tednolan.net wrote:
> > >>>>> I'm pretty sure I've got some programs loading Tcl extensions that
> > >>>>> cd into the directory with the extension dlls, load the extension and then
> > >>>>> change back to where ever they were.
> > >>>>
> > >>>> Hmm.  If so, it's quite a weird way to handle this, rather than
> > >>>> loading the modules with full path.
> > >>>>
> > >>>> Is that a Tcl "feature", or is it how certain Tcl apps are implemented?
> > >>>> I can't really believe the former...
> > >>>
> > >>> This is certainly not a Tcl "feature"!  The standard Tcl extension
> > >>> mechanism always uses the full path simply because Tcl
> > >>> cannot depend on platform-specific ways to search for
> > >>> such libraries elsewhere.
> > >>>
> > >>> I'm willing to test this;I don't believe such a change
> > >>> will break anything in my Tcl environment.
> > >>>
> > >>> Regards,
> > >>>        Jan Nijtmans
> > >
> > > Hmm,
> > >
> > > It's been a while, but I think it is something like the extension is
> > > a DLL, but it depends on another DLL.  Consider for instance, mysqltcl.
> > > If you want to deploy that, you need the mysqltcl.dll and the mysql dll,
> > > so you either have to be in the same dir when you load the extension,
> > > or put that dir in PATH.
> > >
> > > Unfortunately, I can't run a test release on my work machine, or take
> > > my work progs home.
> > 
> > Right, that makes sense. There is indeed no way for the package
> > manager to handle that scenario without external help, such as a PATH
> > variable that includes the various directories these extra DLLs reside
> > in.
> 
> There might be a potential workaround.  Given that Cygwin Tcl calls
> dlopen to load DLLs, we have this somewhat under control.
> 
> The default DLL search algorithm searches the application dir for
> dependent DLLs.  But there's a LoadLibraryEx flag called
> LOAD_WITH_ALTERED_SEARCH_PATH.  When using this flag, and the DLL is
> given with full path, the application dir in the DLL search path is
> replaced by the directory of the DLL.  Thus, dependent DLLs will be
> searched in the same dir the original DLL has been loaded from.
> 
> This could be utilized in dlopen.  If the DLL is given with no path, and
> if LoadLibrary failes, create the full path to the DLL and call
> LoadLibraryEx (full_path, LOAD_WITH_ALTERED_SEARCH_PATH).  DLLs in /bin
> are taken care of by the SetDllDirectory call we're talking about here.

I implemented this in the latest snapshot.  It calls SetDllDirectory
on Cygwin's /bin, and dlopen addiotnally tries to load the DLL with
LoadLibraryEx(LOAD_WITH_ALTERED_SEARCH_PATH) if all else failed.

Please give the latest snapshot from https://cygwin.com/snapshots/
a try.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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