configure: allow adding compiler-specific warning flags

[babeltrace.git] / m4 / ax_compiler_flags_ldflags.m4

diff --git a/m4/ax_compiler_flags_ldflags.m4 b/m4/ax_compiler_flags_ldflags.m4
new file mode 100644 (file)
index 0000000..976d119
--- /dev/null
+++ b/m4/ax_compiler_flags_ldflags.m4
@@ -0,0 +1,111 @@
+# ==============================================================================
+#  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