Alexandre Oliva writes:

This patch arranges for the .so files in say /usr/lib to be soft links
to ../../lib, instead of to /some/arbitrary/pathname/lib.  This
enables seamless relocation of a toolchain containing the development
and run time trees in a sys-root.

Makefile

@@ -186,6 +186,8 @@ tags:
 install: install_runtime install_dev finished2
 
 
+RUNTIME_PREFIX_LIB_FROM_DEVEL_PREFIX_LIB=$(shell extra/scripts/relative_path.sh $(DEVEL_PREFIX)lib $(RUNTIME_PREFIX)lib)
+
 # Installs header files and development library links.
 install_dev:
 	$(INSTALL) -d $(PREFIX)$(DEVEL_PREFIX)lib
@@ -254,11 +256,11 @@ endif
 ifeq ($(strip $(HAVE_SHARED)),y)
 	for i in `find lib/ -type l -name 'lib[a-zA-Z]*.so' | \
 	sed -e 's/lib\///'` ; do \
-		$(LN) -sf $(RUNTIME_PREFIX)lib/$$i.$(MAJOR_VERSION) \
+		$(LN) -sf $(RUNTIME_PREFIX_LIB_FROM_DEVEL_PREFIX_LIB)$$i.$(MAJOR_VERSION) \
 		$(PREFIX)$(DEVEL_PREFIX)lib/$$i; \
 	done;
 ifeq ($(strip $(PTHREADS_DEBUG_SUPPORT)),y)
-	ln -sf $(RUNTIME_PREFIX)lib/libthread_db.so.1 \
+	ln -sf $(RUNTIME_PREFIX_LIB_FROM_DEVEL_PREFIX_LIB)libthread_db.so.1 \
 		$(PREFIX)$(DEVEL_PREFIX)lib/libthread_db.so
 endif
 #	# If we build shared libraries then the static libs are PIC...

extra/scripts/relative_path.sh

@@ -0,0 +1,54 @@
+#! /bin/sh
+# This script computes a relative pathname from $1 to $2
+# They are assumed to not contain . or .. pathname components,
+# but if both directories exist and cd/pwd canonicalizes pathnames,
+# this shouldn't matter.  PWD_CMD may be set to some pwd command that does.
+
+# Copyright 2003 Alexandre Oliva <aoliva@redhat.com>
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+
+from=`(cd $1 > /dev/null && ${PWD_CMD-pwd} || echo $1) 2>/dev/null | sed 's,//*,/,g;s,/*$,,'`
+target=`(cd $2 > /dev/null && ${PWD_CMD-pwd} || echo $2) 2>/dev/null | sed 's,//*,/,g;s,/*$,,'`
+
+case $from in /* | "") ;; *) from=`${PWD_CMD-pwd}`/$from ;; esac
+case $target in /* | "") ;; *) target=`${PWD_CMD-pwd}`/$target ;; esac
+
+case $target in
+"$from" | "$from/"*)
+  dots=`echo $from | sed s,.,.,g`
+  echo $target | sed "s,^$dots/*,,;s,[^/]$,&/,"
+  exit 0
+  ;;
+esac
+
+case $from in
+"$target/"*)
+  dots=`echo $target | sed s,.,.,g`
+  echo $from/ | sed "s,^$dots/*,,;s,[^/]$,&/,;s,[^/]*/*,../,g;s,[^/]$,&/,"
+  exit 0
+  ;;
+esac
+
+prefix=`echo $from///$target | sed 's,\(\(/[^/]*\)*\).*///\1.*,\1,'`
+dots=`echo $prefix | sed s,.,.,g`
+from=`echo $from | sed "s,^$dots,,"`
+target=`echo $target | sed "s,^$dots,,"`
+
+from=`echo $from | sed 's,[^/][^/]*,..,g;s,.$,&/,'`
+echo ${from}$target/
+
+exit 0