# config/check_decls.m4 # This file redefines the standard Autoconf macro AC_CHECK_DECL, # and adds a supporting function _AC_UNDECLARED_WARNING, to make # AC_CHECK_DECLS behave correctly when checking for built-in library # functions with clang. # This is based on commit 82ef7805faffa151e724aa76c245ec590d174580 # in the Autoconf git repository, adapted to work with Autoconf 2.63. # It's still mostly their code, so # it's distributed under Autoconf's license: # This file is part of Autoconf. This program is free # software; you can redistribute it and/or modify it under the # terms of the GNU General Public License as published by the # Free Software Foundation, either version 3 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # Under Section 7 of GPL version 3, you are granted additional # permissions described in the Autoconf Configure Script Exception, # version 3.0, as published by the Free Software Foundation. # # You should have received a copy of the GNU General Public License # and a copy of the Autoconf Configure Script Exception along with # this program; see the files COPYINGv3 and COPYING.EXCEPTION # respectively. If not, see . # Written by David MacKenzie, with help from # Franc,ois Pinard, Karl Berry, Richard Pixley, Ian Lance Taylor, # Roland McGrath, Noah Friedman, david d zuhn, and many others. # _AC_UNDECLARED_WARNING # ---------------------- # Set ac_[]_AC_LANG_ABBREV[]_decl_warn_flag=yes if the compiler uses a warning, # not a more-customary error, to report some undeclared identifiers. Fail when # an affected compiler warns also on valid input. _AC_PROG_PREPROC_WORKS_IFELSE # solves a related problem. AC_DEFUN([_AC_UNDECLARED_WARNING], [# The Clang compiler raises a warning for an undeclared identifier that matches # a compiler builtin function. All extant Clang versions are affected, as of # Clang 3.6.0. Test a builtin known to every version. This problem affects the # C and Objective C languages, but Clang does report an error under C++ and # Objective C++. # # Passing -fno-builtin to the compiler would suppress this problem. That # strategy would have the advantage of being insensitive to stray warnings, but # it would make tests less realistic. AC_CACHE_CHECK([how $CC reports undeclared, standard C functions], [ac_cv_[]_AC_LANG_ABBREV[]_decl_report], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [(void) strchr;])], [AS_IF([test -s conftest.err], [dnl # For AC_CHECK_DECL to react to warnings, the compiler must be silent on # valid AC_CHECK_DECL input. No library function is consistently available # on freestanding implementations, so test against a dummy declaration. # Include always-available headers on the off chance that they somehow # elicit warnings. AC_COMPILE_IFELSE([AC_LANG_PROGRAM([dnl #include #include #include #include extern void ac_decl (int, char *);], [@%:@ifdef __cplusplus (void) ac_decl ((int) 0, (char *) 0); (void) ac_decl; @%:@else (void) ac_decl; @%:@endif ])], [AS_IF([test -s conftest.err], [AC_MSG_FAILURE([cannot detect from compiler exit status or warnings])], [ac_cv_[]_AC_LANG_ABBREV[]_decl_report=warning])], [AC_MSG_FAILURE([cannot compile a simple declaration test])])], [AC_MSG_FAILURE([compiler does not report undeclared identifiers])])], [ac_cv_[]_AC_LANG_ABBREV[]_decl_report=error])]) case $ac_cv_[]_AC_LANG_ABBREV[]_decl_report in warning) ac_[]_AC_LANG_ABBREV[]_decl_warn_flag=yes ;; *) ac_[]_AC_LANG_ABBREV[]_decl_warn_flag= ;; esac ])# _AC_UNDECLARED_WARNING # AC_CHECK_DECL # ------------- # Replace Autoconf 2.63's standard definition of AC_CHECK_DECL, # setting it up to treat warnings as errors if necessary. m4_define([AC_CHECK_DECL], [dnl Initialize each $ac_[]_AC_LANG_ABBREV[]_decl_warn_flag once. AC_DEFUN([_AC_UNDECLARED_WARNING_]_AC_LANG_ABBREV, [_AC_UNDECLARED_WARNING])dnl AC_REQUIRE([_AC_UNDECLARED_WARNING_]_AC_LANG_ABBREV)dnl AS_VAR_PUSHDEF([ac_Symbol], [ac_cv_have_decl_$1])dnl AC_CACHE_CHECK([whether $1 is declared], [ac_Symbol], [ac_save_werror_flag=$ac_[]_AC_LANG_ABBREV[]_werror_flag ac_[]_AC_LANG_ABBREV[]_werror_flag="$ac_[]_AC_LANG_ABBREV[]_decl_warn_flag$ac_[]_AC_LANG_ABBREV[]_werror_flag" AC_COMPILE_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT([$4])], [#ifndef $1 (void) $1; #endif ])], [AS_VAR_SET([ac_Symbol], [yes])], [AS_VAR_SET([ac_Symbol], [no])]) ac_[]_AC_LANG_ABBREV[]_werror_flag=$ac_save_werror_flag]) AS_VAR_IF([ac_Symbol], [yes], [$2], [$3])[]dnl AS_VAR_POPDEF([ac_Symbol])dnl ])# AC_CHECK_DECL