package/patchelf: keep RPATH entries even without DT_NEEDED libraries

package/patchelf: keep RPATH entries even without DT_NEEDED libraries

Our patch
0003-Add-option-to-make-the-rpath-relative-under-a-specif.patch adds
an option --make-rpath-relative, which we use to tweak RPATH of target
binaries.

However, one of the effect of this option is that it drops RPATH
entries if the corresponding directory does not contain a library that
is referenced by a DT_NEEDED entry of the binary.

This unfortunately isn't correct, as RPATH entries are not only used
by the dynamic linker to resolve the location of libraries listed
through DT_NEEDED entries: RPATH entries are also used by dlopen()
when resolving the location of libraries that are loaded at runtime.

Therefore, the removal of RPATH entries that don't correspond to
directories containing libraries referenced by DT_NEEDED entries break
legitimate uses of RPATH for dlopen()ed libraries.

This issue was even pointed out during the review of the upstream pull
request:

  https://github.com/NixOS/patchelf/pull/118#discussion_r329660138

This fixes tst-origin uClibc-ng unit test:

https://github.com/wbx-github/uclibc-ng-test/blob/master/test/dlopen/Makefile.in#L25
https://github.com/wbx-github/uclibc-ng-test/blob/master/test/dlopen/tst-origin.c#L15

Without this patch:

$ gcc -o toto toto.c -Wl,-rpath,/tmp/test/bar
$ readelf -d toto | grep PATH
 0x000000000000000f (RPATH)              Library rpath: [/tmp/test/bar]
$ ./output/host/bin/patchelf --debug --make-rpath-relative /tmp/
toto
patching ELF file `toto'
Kernel page size is 4096 bytes
removing directory '/tmp/test/bar' from RPATH because it does not contain needed libs
new rpath is `'
$ readelf -d toto | grep PATH
 0x000000000000001d (RUNPATH)            Library runpath: []

With the patch applied:

$ gcc -o toto toto.c -Wl,-rpath,/tmp/test/bar
$ readelf -d toto | grep PATH
 0x000000000000000f (RPATH)              Library rpath: [/tmp/test/bar]
$ ./output/host/bin/patchelf --debug --make-rpath-relative /tmp/ toto
patching ELF file `toto'
Kernel page size is 4096 bytes
keeping relative path of /tmp/test/bar
new rpath is `test/bar'
$ readelf -d toto | grep PATH
 0x000000000000001d (RUNPATH)            Library runpath: [test/bar]

Signed-off-by: Yann Sionneau <ysionneau@kalray.eu>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>