From dd77c8383c1a759e909ac3185160cfed6e765b9c Mon Sep 17 00:00:00 2001
From: "Diego E. 'Flameeyes' Pettenò" <flameeyes@gmail.com>
Date: Wed, 19 Nov 2008 03:25:40 +0100
Subject: Check if the linker has an option to refuse undefined references.

This ensures that hte library will be built in a way that will not
fail when --as-needed is used.
---
 configure.ac           |  2 ++
 libasyncns/Makefile.am |  2 +-
 m4/attributes.m4       | 25 +++++++++++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index d6a505e..d08f1b9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -83,6 +83,8 @@ ACF_SEARCH_FUNCTION([res_query], [-lresolv, -lbind],
 
 ACX_PTHREAD
 
+CC_NOUNDEFINED
+
 ZP_LYNX_DOC
 
 AC_CONFIG_FILES([Makefile libasyncns/Makefile doc/Makefile doc/README.html doxygen/Makefile doxygen/doxygen.conf libasyncns.pc])
diff --git a/libasyncns/Makefile.am b/libasyncns/Makefile.am
index 40e989f..0b38163 100644
--- a/libasyncns/Makefile.am
+++ b/libasyncns/Makefile.am
@@ -21,7 +21,7 @@ AM_CFLAGS=-D__EXTENSIONS__ $(PTHREAD_CFLAGS)
 lib_LTLIBRARIES=libasyncns.la
 libasyncns_la_CC=$(PTHREAD_CC)
 libasyncns_la_SOURCES=asyncns.c asyncns.h
-libasyncns_la_LDFLAGS=-version-info $(LIBASYNCNS_VERSION_INFO)
+libasyncns_la_LDFLAGS=-version-info $(LIBASYNCNS_VERSION_INFO) $(LDFLAGS_NOUNDEFINED)
 libasyncns_la_LIBADD=$(PTHREAD_LIBS)
 
 check_PROGRAMS=asyncns-test
diff --git a/m4/attributes.m4 b/m4/attributes.m4
index 45ea789..e86456a 100644
--- a/m4/attributes.m4
+++ b/m4/attributes.m4
@@ -99,6 +99,31 @@ AC_DEFUN([CC_CHECK_LDFLAGS], [
     [$2], [$3])
 ])
 
+dnl define the LDFLAGS_NOUNDEFINED variable with the correct value for
+dnl the current linker to avoid undefined references in a shared object.
+AC_DEFUN([CC_NOUNDEFINED], [
+  dnl We check $host for which systems to enable this for.
+  AC_REQUIRE([AC_CANONICAL_HOST])
+
+  case $host in
+     dnl FreeBSD (et al.) does not complete linking for shared objects when pthreads
+     dnl are requested, as different implementations are present; to avoid problems
+     dnl use -Wl,-z,defs only for those platform not behaving this way.
+     *-freebsd*) ;;
+     *)
+        dnl First of all check for the --no-undefined variant of GNU ld. This allows
+        dnl for a much more readable commandline, so that people can understand what
+        dnl it does without going to look for what the heck -z defs does.
+   	for possible_flags in "-Wl,--no-undefined" "-Wl,-z,defs"; do
+          CC_CHECK_LDFLAGS([$possible_flags], [LDFLAGS_NOUNDEFINED="$possible_flags"])
+	  break
+        done
+	;;
+  esac
+
+  AC_SUBST([LDFLAGS_NOUNDEFINED])
+])
+
 dnl Check for a -Werror flag or equivalent. -Werror is the GCC
 dnl and ICC flag that tells the compiler to treat all the warnings
 dnl as fatal. We usually need this option to make sure that some
-- 
cgit