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

Michael Haubenwallner michael.haubenwallner@ssi-schaefer.com
Mon Aug 29 09:24:00 GMT 2016


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).

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.

/haubi/



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