# ==============================================================================

#  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