[Buildroot] [PATCH v7 09/18] core: add HOST_SANITIZE_RPATH_HOOK to TARGET_FINALIZE_HOOKS

[Samuel Martin <s.martin49@gmail.com>]

This patch adds host-patchelf as a target-finalize dependency, and
introduces the HOST_SANITIZE_RPATH_HOOK hook to fix the ELF files'
RPATH from the HOST_DIR location (excluding the sysroot).

After running this hook, the RPATH from any host ELF files is relative to
the binary location itself.

Notes:
- we avoid to fix RPATH in the sysroot.
- we do not try to fix RPATH in the external toolchain installation
  location as they may have been built in a way, this is already correct;
  furthermore, fixing RPATH in those programs may result in breaking them.
- the whole host directory is processed because a number of
  host-package install programs that could be useful in places
  different from $(HOST_DIR)/{bin,sbin,usr/bin,usr/sbin}.
- the shared libraries are also processed in case they have a 'main'
  function.

As a step toward a fully relocatable SDK, this change allows to get the
toolchain relocatable, but not yet the whole SDK.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>

---
changes v6->v7:
- remove the DEBUG env. var. specific handling in Makefile, now just
  place the variable in the Buildroot environment, to enable debug logs.
  This is documented in a follow-up patch of this series.

changes v5->v6:
- update for the new script version
- add debug mode support

changes v4->v5:
- add verbose support

changes v3->v4:
- add host-patchelf to PACKAGES instead of target-finalize (Baruch)
- add comment

changes v2->v3:
- move hook in Makefile (Baruch)
---
 Makefile | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Makefile b/Makefile
index f1de4ed..268e14e 100644
--- a/Makefile
+++ b/Makefile
@@ -616,6 +616,21 @@ endef
 TARGET_FINALIZE_HOOKS += PURGE_LOCALES
 endif
 
+# RPATH fixing
+# - The host hook sets RPATH in host ELF binaries, using relative paths to the
+#   library locations.
+# - The target hook sanitizes RPATH in target ELF binaries, removing paths
+#   pointing to package's build directories or the sysroot's libdirs.
+PACKAGES += host-patchelf
+
+define HOST_SANITIZE_RPATH_HOOK
+	PATCHELF=$(HOST_DIR)/usr/bin/patchelf \
+	READELF=readelf \
+		$(TOPDIR)/support/scripts/fix-rpath host $(HOST_DIR)
+endef
+
+TARGET_FINALIZE_HOOKS += HOST_SANITIZE_RPATH_HOOK
+
 $(TARGETS_ROOTFS): target-finalize
 
 target-finalize: $(PACKAGES)
-- 
2.7.2