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From b6d16129a525f572ef37d20ba1cd70d59ca4f079 Mon Sep 17 00:00:00 2001
From: Stefan Berger <stefanb@linux.vnet.ibm.com>
Date: Tue, 21 Jul 2020 17:38:10 -0400
Subject: [PATCH 1/2] build-sys: Use AC_COMPILE_IFELSE to check for unused
 linker flags (clang)

This patch fixes a clang issue report in issue #280.

clang does not use ld, so we cannot grep for support of certain linker
flags but have to test-compile.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 configure.ac | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/configure.ac b/configure.ac
index b4d4258..56d3f09 100644
--- a/configure.ac
+++ b/configure.ac
@@ -357,13 +357,25 @@ if test "x$enable_hardening" != "xno"; then
 	if test -z "$TMP1" && test -n "$TPM2"; then
 		HARDENING_CFLAGS="$HARDENING_CFLAGS -D_FORTIFY_SOURCE=2 "
 	fi
-	dnl Check ld for 'relro' and 'now'
-	if $LD --help 2>&1 | $GREP '\-z relro ' > /dev/null; then
-		HARDENING_CFLAGS="$HARDENING_CFLAGS -Wl,-z,relro "
-	fi
-	if $LD --help 2>&1 | $GREP '\-z now ' > /dev/null; then
-		HARDENING_CFLAGS="$HARDENING_CFLAGS -Wl,-z,now "
-	fi
+	dnl Check linker for 'relro' and 'now'
+	save_CFLAGS="$CFLAGS"
+	CFLAGS="-Wl,-z,relro -Werror"
+	AC_MSG_CHECKING([whether linker supports -Wl,-z,relro])
+	AC_COMPILE_IFELSE(
+		[AC_LANG_SOURCE([[int main() { return 0; }]])],
+		[HARDENING_CFLAGS="$HARDENING_CFLAGS -Wl,-z,relro"
+		 AC_MSG_RESULT(yes)],
+		[AC_MSG_RESULT(no)]
+	)
+	CFLAGS="-Wl,-z,now -Werror"
+	AC_MSG_CHECKING([whether linker supports -Wl,-z,now])
+	AC_COMPILE_IFELSE(
+		[AC_LANG_SOURCE([[int main() { return 0; }]])],
+		[HARDENING_CFLAGS="$HARDENING_CFLAGS -Wl,-z,now"
+		 AC_MSG_RESULT(yes)],
+		[AC_MSG_RESULT(no)]
+	)
+	CFLAGS="$save_CFLAGS"
 	AC_SUBST([HARDENING_CFLAGS])
 fi
 
-- 
2.26.2