LD_LIBRARY_PATH overriding -rpath for executable

eldiener · 09-29-2018, 08:19 PM

In a Linux executable I am building with gcc I have linker options setting the rpath with:

'-Wl,-rpath=/some/path'

Yet if LD_LIBRARY_PATH is set to some path which contains the same version number of a shared library which my Linux executable needs at run-time the loader uses that instance of the shared library rather than the one in the directory I am setting with the -rpath linker option above. Why is that ? Does LD_LIBRARY_PATH really override the -rpath path I am setting in the executable itself ? That seems as if it must be a wrong design. How then can I ensure that the executable uses the shared library path which I set in the executable over anything that can be set by an environment variable.

BTW I can of course test that the above is actually happening with the ldd command.

pan64 · 09-30-2018, 01:28 PM

rpath has lower precedence: https://en.wikipedia.org/wiki/Rpath.
or see man ld.so

eldiener · 10-01-2018, 09:57 AM

Quote:

Originally Posted by pan64

rpath has lower precedence: https://en.wikipedia.org/wiki/Rpath.
or see man ld.so

In the Wikipedia link you supplied it says that the rpath is searched first. I do not understand therefore how or why it would have lower precedence.

average_user · 10-01-2018, 02:08 PM

What version of ld do you use? It's possible that you set DT_RUNPATH instead of DT_RPATH. See https://software.intel.com/sites/def.../dsohowto.pdf:

Quote:

For each object, DSO as well as executable, the author can define a
“run path”. The dynamic linker will use the value of the path string
when searching for dependencies of the object the run path is defined
in. Run paths comes is two variants, of which one is deprecated. The
runpaths are accessible through entries in the dynamic section as
field with the tags DT RPATH and DT RUNPATH . The dif- ference between
the two value is when during the search for dependencies they are
used. The DT RPATH value is used first, before any other path,
specifically before the path defined in the LD LIBRARY PATH
environment vari- able. This is problematic since it does not allow
the user to overwrite the value. Therefore DT RPATH is depre-
cated. The introduction of the new variant, DT RUNPATH , corrects this
oversight by requiring the value is used after the path in LD LIBRARY
PATH .

Show output of:

Code:

readelf  -a binary  | grep -i RPATH

eldiener · 10-02-2018, 09:34 AM

Quote:

Originally Posted by average_user

What version of ld do you use? It's possible that you set DT_RUNPATH instead of DT_RPATH. See https://software.intel.com/sites/def.../dsohowto.pdf:

Show output of:

Code:

readelf  -a binary  | grep -i RPATH

Thanks !

I can see from the 'readelf' command that it is setting the RUNPATH rather than the RPATH to what I specify as the '-rpath' option to the linker, and that is why the LD_LIBRARY_PATH is being searched first.

But why would the linker set the RUNPATH rather than the RPATH when I specify '-rpath' in my linker option ? I clearly want the RPATH set since I do not want the end-user to have the ability to override the order of the search path for shared libraries for the executable.

average_user · 10-03-2018, 04:59 AM

Show output of

Code:

ld --version

ld is a part of binutils and I read somewhere that at some point they changed the meaning of -rpath option.