--- /dev/null
+# ==============================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_compiler_flags_ldflags.html
+# ==============================================================================
+#
+# SYNOPSIS
+#
+# AX_COMPILER_FLAGS_LDFLAGS([VARIABLE], [IS-RELEASE], [EXTRA-BASE-FLAGS], [EXTRA-YES-FLAGS])
+#
+# DESCRIPTION
+#
+# Add warning flags for the linker to VARIABLE, which defaults to
+# WARN_LDFLAGS. VARIABLE is AC_SUBST-ed by this macro, but must be
+# manually added to the LDFLAGS variable for each target in the code base.
+#
+# This macro depends on the environment set up by AX_COMPILER_FLAGS.
+# Specifically, it uses the value of $ax_enable_compile_warnings to decide
+# which flags to enable.
+#
+# LICENSE
+#
+# Copyright (c) 2014, 2015 Philip Withnall <philip@tecnocode.co.uk>
+# Copyright (c) 2017, 2018 Reini Urban <rurban@cpan.org>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 9
+
+AC_DEFUN([AX_COMPILER_FLAGS_LDFLAGS],[
+ AX_REQUIRE_DEFINED([AX_APPEND_LINK_FLAGS])
+ AX_REQUIRE_DEFINED([AX_APPEND_FLAG])
+ AX_REQUIRE_DEFINED([AX_CHECK_COMPILE_FLAG])
+ AX_REQUIRE_DEFINED([AX_CHECK_LINK_FLAG])
+
+ # Variable names
+ m4_define([ax_warn_ldflags_variable],
+ [m4_normalize(ifelse([$1],,[WARN_LDFLAGS],[$1]))])
+
+ # Always pass -Werror=unknown-warning-option to get Clang to fail on bad
+ # flags, otherwise they are always appended to the warn_ldflags variable,
+ # and Clang warns on them for every compilation unit.
+ # If this is passed to GCC, it will explode, so the flag must be enabled
+ # conditionally.
+ AX_CHECK_COMPILE_FLAG([-Werror=unknown-warning-option],[
+ ax_compiler_flags_test="-Werror=unknown-warning-option"
+ ],[
+ ax_compiler_flags_test=""
+ ])
+
+ AX_CHECK_LINK_FLAG([-Wl,--as-needed], [
+ AX_APPEND_LINK_FLAGS([-Wl,--as-needed],
+ [AM_LDFLAGS],[$ax_compiler_flags_test])
+ ])
+ AX_CHECK_LINK_FLAG([-Wl,-z,relro], [
+ AX_APPEND_LINK_FLAGS([-Wl,-z,relro],
+ [AM_LDFLAGS],[$ax_compiler_flags_test])
+ ])
+ AX_CHECK_LINK_FLAG([-Wl,-z,now], [
+ AX_APPEND_LINK_FLAGS([-Wl,-z,now],
+ [AM_LDFLAGS],[$ax_compiler_flags_test])
+ ])
+ AX_CHECK_LINK_FLAG([-Wl,-z,noexecstack], [
+ AX_APPEND_LINK_FLAGS([-Wl,-z,noexecstack],
+ [AM_LDFLAGS],[$ax_compiler_flags_test])
+ ])
+ # textonly, retpolineplt not yet
+
+ # macOS and cygwin linker do not have --as-needed
+ AX_CHECK_LINK_FLAG([-Wl,--no-as-needed], [
+ ax_compiler_flags_as_needed_option="-Wl,--no-as-needed"
+ ], [
+ ax_compiler_flags_as_needed_option=""
+ ])
+
+ # macOS linker speaks with a different accent
+ ax_compiler_flags_fatal_warnings_option=""
+ AX_CHECK_LINK_FLAG([-Wl,--fatal-warnings], [
+ ax_compiler_flags_fatal_warnings_option="-Wl,--fatal-warnings"
+ ])
+ AX_CHECK_LINK_FLAG([-Wl,-fatal_warnings], [
+ ax_compiler_flags_fatal_warnings_option="-Wl,-fatal_warnings"
+ ])
+
+ # Base flags
+ AX_APPEND_LINK_FLAGS([ dnl
+ $ax_compiler_flags_as_needed_option dnl
+ $3 dnl
+ ],ax_warn_ldflags_variable,[$ax_compiler_flags_test])
+
+ AS_IF([test "$ax_enable_compile_warnings" != "no"],[
+ # "yes" flags
+ AX_APPEND_LINK_FLAGS([$4 $5 $6 $7],
+ ax_warn_ldflags_variable,
+ [$ax_compiler_flags_test])
+ ])
+ AS_IF([test "$ax_enable_compile_warnings" = "error"],[
+ # "error" flags; -Werror has to be appended unconditionally because
+ # it's not possible to test for
+ #
+ # suggest-attribute=format is disabled because it gives too many false
+ # positives
+ AX_APPEND_LINK_FLAGS([ dnl
+ $ax_compiler_flags_fatal_warnings_option dnl
+ ],ax_warn_ldflags_variable,[$ax_compiler_flags_test])
+ ])
+
+ # Substitute the variables
+ AC_SUBST(ax_warn_ldflags_variable)
+])dnl AX_COMPILER_FLAGS