About the dll search algorithm of dlopen (patch-r3)

Corinna Vinschen corinna-cygwin@cygwin.com
Tue Aug 30 13:35:00 GMT 2016


On Aug 29 11:24, Michael Haubenwallner wrote:
> Hi Corinna,
> 
> On 08/26/2016 02:04 PM, Corinna Vinschen wrote:
> > On Aug 25 19:48, Michael Haubenwallner wrote:
> >> On 08/22/2016 08:37 PM, Corinna Vinschen wrote:
> >>> (*) Yuk!  Do we really, *really* want that?  The redirection from
> >>>     /usr/lib to /usr/bin is only done for system libs, and only because
> >>>     otherwise we had trouble starting Cygwin from CMD or the Explorer
> >>>     GUI "Run..." box.  We can't change this without breaking everything
> >>>     since we *do* depend on the Windows loader yet.
> >>>     
> >>>     However, as long as this is restricted to /usr/lib, /usr/bin, it's a
> >>>     closed system under control of "the distro".  If you extend this to
> >>>     *any* external path ending in "lib", isn't it inherently dangerous
> >>>     to automate this under the hood, without the application's consent?
> >>>     Or, FWIW, the user's consent in case of LD_LIBRARY_PATH?
> >>
> >> 've split into add_lib_searchdir (), used for "/usr/lib" only.
> > 
> > Btw., I just noticed something interesting, independently of your patch.
> > Consider the file /usr/bin/cygz.dll:
> > 
> > - dlopen (libz.so)            success
> > 
> > - dlopen (/usr/bin/libz.so)   success
> > 
> > - dlopen (/usr/lib/libz.so)   fails
> > 
> > That's pretty clear when looking through the code, but... wouldn't
> > it make sense to allow that?  If a path is given, and the path points
> > to /usr/lib, search the file in /usr/bin as well?
> 
> Easy enough - but this should apply to any prefix IMO: While the
> application specific prefix often isn't /usr - but something like
> /usr/local or /opt/application, application specific libs may be
> built & installed with libtool or something similar as well - at
> least some tool that knows about installing the real dll into
> <app-prefix>/bin (because of the missing Cygwin loader).

You have a point there.

> But agreed, it makes sense doing /lib->/bin for the explicit path and
> the /usr/lib default only and not for the environment-provided paths.

It feels certainly more safe to restrict this to the system path for
now.  But... yeah, you have a point.

Not well thought out, just an idea kicking around:

Apart from the obvious system path handling, what if other lib->bin
transitions only take place if the calling application is installed
in that very bin dir...?


Corinna

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