Merge pull request #275 from cstes/ax_cc_tentdef

ax_cc_tentdef: test for C tentative definitions

2 files changed, 177 insertions, 0 deletions

diff --git a/m4/ax_cc_attrcommon.m4 b/m4/ax_cc_attrcommon.m4
new file mode 100644
index 0000000..f6b22fd
--- /dev/null
+++ b/m4/ax_cc_attrcommon.m4
@@ -0,0 +1,76 @@
+# ===========================================================================
+#       https://www.gnu.org/software/autoconf-archive
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CC_ATTRCOMMON
+#
+# DESCRIPTION
+#
+#   Determine whether the C compiler supports C tentative defintions
+#   with __attribute((__common__))
+#   See K&R book Appendix A10.2 on 'extern' and tentative definitions.
+#   Some compilers use a 'strict definition-reference model'
+#   Traditionally most UNIX C compilers support C tentative definitions.
+#   GCC 10 switched from default fcommon to fnocommon
+#   and will need __attribute__ ((__common__)) for tentative definitions.
+#
+#   The $ac_cv_attrcommon variable will be either yes or no,
+#   and can be overridden on the command line with using --with-attrcommon
+#
+#   See also:  ax_cc_tentdef.m4 for a test on C tentative definitions
+#
+# LICENSE
+#
+#   Copyright (c) 1996-2023 David Stes
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+
+#serial 1
+
+AC_ARG_WITH(attrcommon,
+  [  --with-attrcommon       use __attribute__ for C tentative definitions],
+  [ac_cv_attrcommon=$withval]
+)
+
+AC_DEFUN([AX_CC_ATTRCOMMON],
+[
+AC_MSG_CHECKING(whether compiler supports __attribute__((__common__)))
+AC_CACHE_VAL(ac_cv_attrcommon,[
+t1="ac$$.c"
+o1="ac$$.o"
+ac_clean_files="$t1 $o1"
+cat >$t1 <<EOF
+__attribute__((__common__)) int a = 7;
+EOF
+# tentative definitions are resolved using 'common storage'
+# this is the traditional case for most C compilers (K&R book Appendix A10.2)
+# this case is supported by setting CC to 'gcc -fcommon'
+# which is since gcc 10 not the default (it defaults now to -fno-common)
+echo "$CC -c $t1" >&5
+if $CC -c $t1 2>&5 1>&5
+  then
+    echo " (no)" >&5
+    ac_cv_attrcommon=yes;
+  else
+    echo " (yes)" >&5
+    ac_cv_attrcommon=no;
+fi
+rm -rf $ac_clean_files
+],ac_cv_attrcommon=yes,ac_cv_attrcommon=no)
+AC_MSG_RESULT($ac_cv_attrcommon)
+])
+
+
diff --git a/m4/ax_cc_tentdef.m4 b/m4/ax_cc_tentdef.m4
new file mode 100644
index 0000000..9171dea
--- /dev/null
+++ b/m4/ax_cc_tentdef.m4
@@ -0,0 +1,101 @@
+# ===========================================================================
+#       https://www.gnu.org/software/autoconf-archive/
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CC_TENTDEF
+#
+# DESCRIPTION
+#
+#   Determine whether the C compiler supports C tentative defintions.
+#   See K&R book Appendix A10.2 on 'extern' and tentative definitions.
+#   Some compilers use a 'strict definition-reference model'
+#   Traditionally most UNIX C compilers support tentative definitions,
+#   whereas some compiler such as Metrowerks or WATCOM C do not.
+#
+#   The $ac_cv_tentdef variable will be either no or yes,
+#   and can be overridden on the command line using --with-tentdef
+#
+#   See also:  ax_cc_attrcommon.m4 for a __attribute__(( __common__)) test
+#
+# LICENSE
+#
+#   Copyright (c) 1996-2023 David Stes
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+
+#serial 1
+
+AC_ARG_WITH(tentdef,
+  [  --with-tentdef          use C tentative definitions],
+  [ac_cv_tentdef=$withval]
+)
+
+AC_DEFUN([AX_CC_TENTDEF],
+[
+AC_MSG_CHECKING(whether compiler supports C tentative definitions)
+AC_CACHE_VAL(ac_cv_tentdef,[
+t1="x$$.c"
+t2="y$$.c"
+e1="x$$"
+e2="y$$"
+ac_clean_files="$e1 $e2 $t1 $t2"
+
+# this is the traditional case for most compilers (K&R book Appendix A10.2)
+# tentative definitions are resolved using 'common storage'
+# this case is supported by setting CC to 'gcc -fcommon'
+# which is since gcc 10 not the default (it defaults now to -fno-common)
+cat >$t1 <<EOF
+int a = 7;
+EOF
+
+cat >$t2 <<EOF
+#include <stdio.h>
+int a;
+int main() { exit(a);return a; }
+EOF
+
+echo "$CC $t1 $t2 -o $e1" >&5
+($CC $t1 $t2 -o $e1) 2>&5 1>&5
+echo "$CC $t2 $t1 -o $e2" >&5
+($CC $t2 $t1 -o $e2) 2>&5 1>&5
+
+if test -x ./$e1 -a -x ./$e2
+then
+  echo -n "check whether $e1 returns '7'" >&5
+  if ./$e1 != 7
+  then
+    echo " (no)" >&5
+    ac_cv_tentdef=no;
+  else
+    echo " (yes)" >&5
+    echo -n "check whether $e2 returns '7'" >&5
+    if ./$e2 != 7
+    then
+     echo " (no)" >&5
+     ac_cv_tentdef=no
+    else
+     echo " (yes)" >&5
+     ac_cv_tentdef=yes;
+    fi
+  fi
+else
+  ac_cv_tentdef=no;
+fi
+rm -rf $ac_clean_files
+],ac_cv_tentdef=no,ac_cv_tentdef=yes)
+AC_MSG_RESULT($ac_cv_tentdef)
+])
+