Dr. David Kirkby wrote:
> Georg S. Weber wrote:
>> Hmm,
>>
>> I don't quite get the point of your message.
>
> Sorry,
>
> I was trying to get some discussion, and hopefully understanding, of why
> these
> issues arise, with a hope to trying to fix them. It's clear the present
> situation has 'issues' and to my knowledge, nobody has a foolproof way of
> building Sage without having to rely on 'hacks' on some operating systems.
>
>> "Installing the dynamic library somewhere else and link it in by ...
>> adding said library to the users LD_LIBRARY_PATH ..."
>>
>> is pretty much exactly the way things are designed and supposed to
>> work (and actually do work to a large extent) in Sage. I don't think
>> LD_PRELOAD in its various incarnations is portable enough for the Sage
>> purposes (I haven't checked though).
>
> LD_LIBRARY_PATH tells the program where to look for libraries it can't find.
> I'm
> not aware of how it is supposed to behave if there are system libraries and
> libraries of the same name in LD_LIBRARY_PATH. Can we be sure that system
> libraries will be used in preference to those in LD_LIBRARY_PATH, or can we
> be
> sure those in LD_LIBRARY_PATH will be used in preference to those in the
> system?
> It seems to me, if the library is on the system in somewhere like /usr/lib,
> then it will be loaded from there, despite the fact LD_LIBRARY_PATH might
> specify a location where another copy resides.
>
> For Solaris at least, LD_PRELOAD can be used to force something to be loaded
> in
> preference to what exists on the system. I've no idea how portable that is.
> I'm
> not suggesting it is the way forward.
>
While not a guarantee, here's what I get from the manpage of ld.so on
Ubuntu (x86_64):
The necessary shared libraries needed by the program are searched for
in the following order
* Using the environment variable LD_LIBRARY_PATH
(LD_AOUT_LIBRARY_PATH for a.out programs). Except if the exe‐
cutable is a setuid/setgid binary, in which case it is ignored.
* From the cache file /etc/ld.so.cache which contains a compiled
list of candidate libraries previously found in the augmented
library path.
* In the default path /lib, and then /usr/lib.
So it looks like, for Linux, at least, setting LD_LIBRARY_PATH is
sufficient.
Also, there's this:
LD_PRELOAD
A whitespace-separated list of additional, user-specified, ELF
shared libraries to be loaded before all others. This can be
used to selectively override functions in other shared
libraries. For setuid/setgid ELF binaries, only libraries in
the standard search directories that are also setgid will be
loaded.
I don't know very much about these issues, but the above might help, at
least for (Ubuntu) linux.
Jason
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