correct usage of rpath (relative vs absolute)

Question

When building a binary or library, specifying the rpath, i.e.

-Wl,rpath,

tells the linker where to find the

Answer 1

In the case of rpath, it makes no sense to use a relative path, since a relative path will be relative to the current working directory, NOT relative to the directory where the binary/library was found. So it simply won't work for executables found in $PATH or libraries in pretty much any case.

Instead, you can use the $ORIGIN "special" path to have a path relative to the executable with
-Wl,-rpath,'$ORIGIN' -- note that you need quotes around it to avoid having the shell interpret it as a variable, and if you try to do this in a Makefile, you need $$ to avoid having make interpret the $ as well.

Answer 2

What is the UNIX philosphy regarding absolute and relative paths here?

Using relative path makes an executable that only works when invoked from a particular directory, which is almost never what you want. E.g. if the executable is in /app/foo/bin/exe and has DT_RUNPATH of lib/, and a dependent library is in /app/foo/lib/libfoo.so, then the exe would only run when invoked from /app/foo, and not when invoked from any other directory.

Using absolute path is much better: you can do cd /tmp; /app/foo/bin/exe and have the executable still work. This is still however less than ideal: you can't easily have multiple versions of the binary (important during development), and you dictate to end-users where they must install the package.

On systems that support $ORIGIN, using DT_RUNPATH of $ORIGIN/../lib would give you an executable what works when installed anywhere and invoked from any directory, so long as relative paths to bin/ and lib/ are preserved.