From 6c10f89e825f80f027fac2cb3b3b0b86bcd1d7ef Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 16 Feb 2020 12:39:39 +0000
Subject: [PATCH] configure[.ac]: Arrange to cope with jessie's gcc

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 configure    | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac | 22 ++++++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/configure b/configure
index 43de16e..152c8ed 100755
--- a/configure
+++ b/configure
@@ -4132,6 +4132,54 @@ fi
 done
 
 
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking required gcc -std flag" >&5
+$as_echo_n "checking required gcc -std flag... " >&6; }
+if ${secnet_cv_gcc_std_flag+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    secnet_cv_gcc_std_flag=""
+    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+void x(void) { for (int i=0; i<1; i++) { } }
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+else
+
+        old_cflags="$CFLAGS"
+	CFLAGS="$CFLAGS -std=gnu11"
+	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+void x(void) { for (int i=0; i<1; i++) { } }
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+	    secnet_cv_gcc_std_flag=" -std=gnu11"
+
+else
+
+	    { $as_echo "$as_me:${as_lineno-$LINENO}: result: failure!" >&5
+$as_echo "failure!" >&6; }
+	    as_fn_error 1 "cannot get test program to compile" "$LINENO" 5
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	CFLAGS="$old_cflags"
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $secnet_cv_gcc_std_flag" >&5
+$as_echo "$secnet_cv_gcc_std_flag" >&6; }
+CFLAGS="$CFLAGS$secnet_cv_gcc_std_flag"
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: Checking requirements for IPv6 support..." >&5
 $as_echo "$as_me: Checking requirements for IPv6 support..." >&6;}
 enable_ipv6=true
diff --git a/configure.ac b/configure.ac
index 674ed36..471a6e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -102,6 +102,28 @@ REQUIRE_HEADER([adns.h])
 
 AC_CHECK_FUNCS([fmemopen funopen])
 
+dnl gcc 4.9.2 (jessie) requires -std=gnu11 to cope with for (int i=...
+dnl but we do not want to pass that everywhere because we don't want
+dnl to nail down the C dialect this way.  Why oh why oh why.
+m4_define([for_gcc_std],[
+void x(void) { for (int i=0; i<1; i++) { } }
+])
+AC_CACHE_CHECK([required gcc -std flag],[secnet_cv_gcc_std_flag],[
+    secnet_cv_gcc_std_flag=""
+    AC_COMPILE_IFELSE([AC_LANG_SOURCE(for_gcc_std)],[],[
+        old_cflags="$CFLAGS"
+	CFLAGS="$CFLAGS -std=gnu11"
+	AC_COMPILE_IFELSE([AC_LANG_SOURCE(for_gcc_std)],[
+	    secnet_cv_gcc_std_flag=" -std=gnu11"
+	],[
+	    AC_MSG_RESULT([failure!])
+	    AC_MSG_ERROR([cannot get test program to compile],1)
+	])
+	CFLAGS="$old_cflags"
+    ])
+])
+CFLAGS="$CFLAGS$secnet_cv_gcc_std_flag"
+
 AC_MSG_NOTICE([Checking requirements for IPv6 support...])
 enable_ipv6=true
 m4_define(NO_IPV6,[enable_ipv6=false])
-- 
2.30.2