[PATCH v2] Check if rpath is supported before setting it

[Ulf Hermann <ulf dot hermann at qt dot io>]

Some systems don't have rpath. In that case the backends need to be
made available by some external mechanism. Provide a configure switch
to explicitly turn off the setting of rpaths. Throw an error if that is
not set and rpath is not supported.

Signed-off-by: Ulf Hermann <ulf.hermann@qt.io>
---
 ChangeLog         |  5 +++++
 configure.ac      | 22 ++++++++++++++++++++++
 libdw/ChangeLog   |  4 ++++
 libdw/Makefile.am |  9 +++++++--
 4 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 22c46c6..344ae0b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2017-05-03  Ulf Hermann  <ulf.hermann@qt.io>
 
+	* configure.ac: Check if the linker supports -rpath and add a switch
+	to disable setting of rpath.
+
+2017-05-03  Ulf Hermann  <ulf.hermann@qt.io>
+
 	* configure.ac: Test if symbol versioning is supported.
 
 2017-04-27  Ulf Hermann  <ulf.hermann@qt.io>
diff --git a/configure.ac b/configure.ac
index 48b06de..598b372 100644
--- a/configure.ac
+++ b/configure.ac
@@ -204,6 +204,28 @@ fi
 
 AC_SUBST([dso_LDFLAGS])
 
+AC_ARG_ENABLE([rpath],
+AS_HELP_STRING([--disable-rpath], [Disable setting of rpath]))
+
+AC_CACHE_CHECK([for rpath support], ac_cv_rpath, [dnl
+save_LDFLAGS="$LDFLAGS"
+LDFLAGS="$save_LDFLAGS -Wl,--enable-new-dtags,-rpath,/foo/bar"
+AC_LINK_IFELSE([AC_LANG_PROGRAM()], ac_cv_rpath=yes, ac_cv_rpath=no)
+LDFLAGS="$save_LDFLAGS"
+])
+if test "$ac_cv_rpath" = "no"; then
+    if test "x$enable_rpath" != "xno"; then
+        AC_MSG_ERROR([rpath is not supported.
+                      Use --disable-rpath to build without.])
+    fi
+fi
+
+AM_CONDITIONAL(RPATH, [test "x$enable_rpath" != "xno"])
+AS_IF([test "x$enable_rpath" = "xno"],
+      [AC_MSG_WARN([Disabling rpath prevents libdw from automatically 
+                    finding the ebl backends.])
+       enable_rpath=no],[enable_rpath=yes])
+
 AC_CACHE_CHECK([for __thread support], ac_cv_tls, [dnl
 # Use the same flags that we use for our DSOs, so the test is representative.
 # Some old compiler/linker/libc combinations fail some ways and not others.
diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index af4aa40..d33ffe3 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2017-02-28  Ulf Hermann  <ulf.hermann@qt.io>
+
+	* Makefile.am: Don't set rpath if it's disabled.
+
 2017-02-27  Ulf Hermann  <ulf.hermann@qt.io>
 
 	* libdwP.h: Use attribute_hidden.
diff --git a/libdw/Makefile.am b/libdw/Makefile.am
index 31f7012..055e3f1 100644
--- a/libdw/Makefile.am
+++ b/libdw/Makefile.am
@@ -99,6 +99,12 @@ $(srcdir)/known-dwarf.h: $(top_srcdir)/config/known-dwarf.awk $(srcdir)/dwarf.h
 	mv -f $@.new $@
 endif
 
+if RPATH
+PKG_RPATH = -Wl,--enable-new-dtags,-rpath,$(pkglibdir)
+else
+PKG_RPATH =
+endif
+
 libdw_pic_a_SOURCES =
 am_libdw_pic_a_OBJECTS = $(libdw_a_SOURCES:.c=.os)
 
@@ -115,8 +121,7 @@ libdw.so$(EXEEXT): $(srcdir)/libdw.map libdw_pic.a ../libdwelf/libdwelf_pic.a \
 # The rpath is necessary for libebl because its $ORIGIN use will
 # not fly in a setuid executable that links in libdw.
 	$(AM_V_CCLD)$(LINK) $(dso_LDFLAGS) -o $@ -Wl,--soname,$@.$(VERSION) \
-		-Wl,--enable-new-dtags,-rpath,$(pkglibdir) \
-		-Wl,--version-script,$<,--no-undefined \
+		-Wl,--version-script,$<,--no-undefined $(PKG_RPATH) \
 		-Wl,--whole-archive $(filter-out $<,$^) -Wl,--no-whole-archive\
 		-ldl -lz $(intl_LDADD) $(zip_LIBS) $(libgnu)
 	@$(textrel_check)
-- 
2.1.4