From 51776b297e04dabb24b7b645744da7100f85ff2e Mon Sep 17 00:00:00 2001
From: Beniamino Galvani <bgalvani@redhat.com>
Date: Tue, 4 Sep 2018 10:25:19 +0200
Subject: [PATCH] build: don't change CFLAGS from configure.ac

If configure.ac automatically adds compiler flags to CFLAGS, it
becomes hard to override one of them for a specific target because
CFLAGS is added last. It is better to use AM_CFLAGS. See [1].

[1] https://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
---
 configure.ac           |  5 +++--
 m4/compiler_options.m4 | 10 +++++-----
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/configure.ac b/configure.ac
index b3fc8b249f..e080d359cc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1043,7 +1043,7 @@ else
 	more_logging_default=no
 fi
 
-NM_COMPILER_WARNINGS(CFLAGS, ${more_warnings_default})
+NM_COMPILER_WARNINGS(AM_CFLAGS, ${more_warnings_default})
 
 NM_COMPILER_FLAG(LIBSYSTEMD_NM_CFLAGS, "-Wno-gnu-variable-sized-type-not-at-end")
 AC_SUBST(LIBSYSTEMD_NM_CFLAGS)
@@ -1051,7 +1051,7 @@ AC_SUBST(LIBSYSTEMD_NM_CFLAGS)
 CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
 	-fno-strict-aliasing \
 ])
-CFLAGS="$CFLAGS $with_cflags"
+AM_CFLAGS="$AM_CFLAGS $with_cflags"
 
 AC_ARG_ENABLE(more-asserts,
               AS_HELP_STRING([--enable-more-asserts],
@@ -1248,6 +1248,7 @@ fi
 
 AM_CONDITIONAL(BUILD_DOCS, test "$build_docs" = "yes")
 AM_CONDITIONAL(HAVE_DOCS, test "$build_docs" = "yes" -o "$use_pregen_docs" = "yes")
+AC_SUBST(AM_CFLAGS)
 
 AC_CONFIG_FILES([
 Makefile
diff --git a/m4/compiler_options.m4 b/m4/compiler_options.m4
index 0683e44e38..1f283db692 100644
--- a/m4/compiler_options.m4
+++ b/m4/compiler_options.m4
@@ -31,7 +31,7 @@ AC_DEFUN([NM_COMPILER_FLAG], [
 
 dnl Check whether a particular warning is not emitted with code provided,
 dnl append an option to disable the warning to a specified variable if the check fails.
-dnl NM_COMPILER_WARNING([ENV-VAR], [C-SNIPPET], [WARNING]])
+dnl NM_COMPILER_WARNING([ENV-VAR], [WARNING], [C-SNIPPET])
 AC_DEFUN([NM_COMPILER_WARNING], [
         _NM_COMPILER_FLAG([-W$2], [$3], [eval "AS_TR_SH([$1])='$$1 -W$2'"], [eval "AS_TR_SH([$1])='$$1 -Wno-$2'"])
 ])
@@ -47,10 +47,10 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
 
 	dnl This is enabled in clang by default, makes little sense,
 	dnl and causes the build to abort with -Werror.
-	CFLAGS_SAVED="$$1"
-	eval "AS_TR_SH([$1])='$$1 -Qunused-arguments'"
-	AC_COMPILE_IFELSE([AC_LANG_SOURCE([])], [], eval "AS_TR_SH([$1])='$CFLAGS_SAVED'")
-	unset CFLAGS_SAVED
+	CFLAGS_SAVED="$CFLAGS"
+	CFLAGS="$CFLAGS -Qunused-arguments"
+	AC_COMPILE_IFELSE([AC_LANG_SOURCE([])], eval "AS_TR_SH([$1])='$$1 -Qunused-arguments'", [])
+	CFLAGS="$CFLAGS_SAVED"
 
 	dnl clang only warns about unknown warnings, unless
 	dnl called with "-Werror=unknown-warning-option"