slot-ref, slot-set! et al bypass "using-class" variants
[bpt/guile.git] / acinclude.m4
index 6a56d26..6a1470f 100644 (file)
@@ -1,7 +1,30 @@
+dnl -*- Autoconf -*-
+
+dnl Copyright (C) 1997, 1999, 2000, 2001, 2002, 2004, 2006,
+dnl   2007, 2008, 2009, 2010, 2011, 2013 Free Software Foundation, Inc.
+dnl
+dnl This file is part of GUILE
+dnl
+dnl GUILE is free software; you can redistribute it and/or modify it under
+dnl the terms of the GNU Lesser General Public License as published by the
+dnl Free Software Foundation; either version 3, or (at your option) any
+dnl later version.
+dnl
+dnl GUILE is distributed in the hope that it will be useful, but WITHOUT
+dnl ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+dnl FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+dnl License for more details.
+dnl
+dnl You should have received a copy of the GNU Lesser General Public
+dnl License along with GUILE; see the file COPYING.LESSER.  If not, write
+dnl to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
+dnl Floor, Boston, MA 02110-1301, USA.
+
+
 dnl  On the NeXT, #including <utime.h> doesn't give you a definition for
 dnl  struct utime, unless you #define _POSIX_SOURCE.
 
-AC_DEFUN(GUILE_STRUCT_UTIMBUF, [
+AC_DEFUN([GUILE_STRUCT_UTIMBUF], [
   AC_CACHE_CHECK([whether we need POSIX to get struct utimbuf],
     guile_cv_struct_utimbuf_needs_posix,
     [AC_TRY_CPP([
@@ -15,7 +38,9 @@ struct utime blah;
                 guile_cv_struct_utimbuf_needs_posix=no,
                guile_cv_struct_utimbuf_needs_posix=yes)])
   if test "$guile_cv_struct_utimbuf_needs_posix" = yes; then
-     AC_DEFINE(UTIMBUF_NEEDS_POSIX)
+     AC_DEFINE([UTIMBUF_NEEDS_POSIX], 1,
+       [Define this if <utime.h> doesn't define struct utimbuf unless
+        _POSIX_SOURCE is defined.  See GUILE_STRUCT_UTIMBUF in aclocal.m4.])
   fi])
 
 
@@ -32,12 +57,12 @@ AC_DEFUN([GUILE_HEADER_LIBC_WITH_UNISTD],
   [
     AC_CHECK_HEADERS(libc.h unistd.h)
     AC_CACHE_CHECK(
-      "whether libc.h and unistd.h can be included together",
+      [whether libc.h and unistd.h can be included together],
       guile_cv_header_libc_with_unistd,
       [
         if test "$ac_cv_header_libc_h" = "no"; then
           guile_cv_header_libc_with_unistd="no"
-        elif test "$ac_cv_header_unistd.h" = "no"; then
+        elif test "$ac_cv_header_unistd_h" = "no"; then
           guile_cv_header_libc_with_unistd="yes"
         else
           AC_TRY_COMPILE(
@@ -53,7 +78,11 @@ AC_DEFUN([GUILE_HEADER_LIBC_WITH_UNISTD],
       ]
     )
     if test "$guile_cv_header_libc_with_unistd" = yes; then
-      AC_DEFINE(LIBC_H_WITH_UNISTD_H)
+      AC_DEFINE([LIBC_H_WITH_UNISTD_H], 1,
+        [Define this if we should include <libc.h> when we've already
+         included <unistd.h>.  On some systems, they conflict, and libc.h
+         should be omitted.  See GUILE_HEADER_LIBC_WITH_UNISTD in
+         aclocal.m4.])
     fi
   ]
 )
@@ -65,7 +94,7 @@ dnl with other parameters, such as libraries, varying.
 dnl
 dnl GUILE_NAMED_CHECK_FUNC(FUNCTION, TESTNAME,
 dnl                        [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]])
-AC_DEFUN(GUILE_NAMED_CHECK_FUNC,
+AC_DEFUN([GUILE_NAMED_CHECK_FUNC],
 [AC_MSG_CHECKING([for $1])
 AC_CACHE_VAL(ac_cv_func_$1_$2,
 [AC_TRY_LINK(
@@ -76,11 +105,10 @@ dnl select.  Similarly for bzero.
     which can conflict with char $1(); below.  */
 #include <assert.h>
 /* Override any gcc2 internal prototype to avoid an error.  */
-]ifelse(AC_LANG, CPLUSPLUS, [#ifdef __cplusplus
+#ifdef __cplusplus
 extern "C"
 #endif
-])dnl
-[/* We use char because int might match the return type of a gcc2
+/* We use char because int might match the return type of a gcc2
     builtin and then its argument prototype would still apply.  */
 char $1();
 ], [
@@ -105,38 +133,446 @@ fi
 
 
 
-dnl Check checks whether dlsym (if present) requires a leading underscore.
-dnl Written by Dan Hagerty <hag@ai.mit.edu> for scsh-0.5.0.
-AC_DEFUN(GUILE_DLSYM_USCORE, [
-  AC_MSG_CHECKING(for underscore before symbols)
-  AC_CACHE_VAL(guile_cv_uscore,[
-    echo "main(){int i=1;}
-    fnord(){int i=23; int ltuae=42;}" > conftest.c
-    ${CC} conftest.c > /dev/null
-    if (nm a.out | grep _fnord) > /dev/null; then
-      guile_cv_uscore=yes
-    else
-      guile_cv_uscore=no
-    fi])
-  AC_MSG_RESULT($guile_cv_uscore)
-  rm -f conftest.c a.out
-
-  if test $guile_cv_uscore = yes; then
-    AC_DEFINE(USCORE)
-
-    if test $ac_cv_func_dlopen = yes -o $ac_cv_lib_dl_dlopen = yes ; then
-       AC_MSG_CHECKING(whether dlsym always adds an underscore for us)
-       AC_CACHE_VAL(guile_cv_dlsym_adds_uscore,AC_TRY_RUN( [
-#include <dlfcn.h>
-#include <stdio.h>
-fnord() { int i=42;}
-main() { void *self, *ptr1, *ptr2; self=dlopen(NULL,RTLD_LAZY);
-    if(self) { ptr1=dlsym(self,"fnord"); ptr2=dlsym(self,"_fnord");
-    if(ptr1 && !ptr2) exit(0); } exit(1); } 
-], [guile_cv_dlsym_adds_uscore=yes
-       AC_DEFINE(DLSYM_ADDS_USCORE) ], guile_cv_dlsym_adds_uscore=no))
-
-        AC_MSG_RESULT($guile_cv_dlsym_adds_uscore)
+
+dnl Available from the Autoconf Macro Archive at:
+dnl http://autoconf-archive.cryp.to/acx_pthread.html
+dnl
+AC_DEFUN([ACX_PTHREAD], [
+AC_REQUIRE([AC_CANONICAL_HOST])
+AC_LANG_SAVE
+AC_LANG_C
+acx_pthread_ok=no
+
+# We used to check for pthread.h first, but this fails if pthread.h
+# requires special compiler flags (e.g. on True64 or Sequent).
+# It gets checked for in the link test anyway.
+
+# First of all, check if the user has set any of the PTHREAD_LIBS,
+# etcetera environment variables, and if threads linking works using
+# them:
+if test x"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then
+        save_CFLAGS="$CFLAGS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        save_LIBS="$LIBS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        AC_MSG_CHECKING([for pthread_join in LIBS=$PTHREAD_LIBS with CFLAGS=$PTHREAD_CFLAGS])
+        AC_TRY_LINK_FUNC(pthread_join, acx_pthread_ok=yes)
+        AC_MSG_RESULT($acx_pthread_ok)
+        if test x"$acx_pthread_ok" = xno; then
+                PTHREAD_LIBS=""
+                PTHREAD_CFLAGS=""
+        fi
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+fi
+
+# We must check for the threads library under a number of different
+# names; the ordering is very important because some systems
+# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
+# libraries is broken (non-POSIX).
+
+# Create a list of thread flags to try.  Items starting with a "-" are
+# C compiler flags, and other items are library names, except for "none"
+# which indicates that we try without any flags at all, and "pthread-config"
+# which is a program returning the flags for the Pth emulation library.
+
+acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
+
+# The ordering *is* (sometimes) important.  Some notes on the
+# individual items follow:
+
+# pthreads: AIX (must check this before -lpthread)
+# none: in case threads are in libc; should be tried before -Kthread and
+#       other compiler flags to prevent continual compiler warnings
+# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
+# -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
+# lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
+# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads)
+# -pthreads: Solaris/gcc
+# -mthreads: Mingw32/gcc, Lynx/gcc
+# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
+#      doesn't hurt to check since this sometimes defines pthreads too;
+#      also defines -D_REENTRANT)
+#      ... -mt is also the pthreads flag for HP/aCC
+# pthread: Linux, etcetera
+# --thread-safe: KAI C++
+# pthread-config: use pthread-config program (for GNU Pth library)
+
+case "${host_cpu}-${host_os}" in
+        *solaris*)
+
+        # On Solaris (at least, for some versions), libc contains stubbed
+        # (non-functional) versions of the pthreads routines, so link-based
+        # tests will erroneously succeed.  (We need to link with -pthreads/-mt/
+        # -lpthread.)  (The stubs are missing pthread_cleanup_push, or rather
+        # a function called by this macro, so we could check for that, but
+        # who knows whether they'll stub that too in a future libc.)  So,
+        # we'll just look for -pthreads and -lpthread first:
+
+        acx_pthread_flags="-pthreads pthread -mt -pthread $acx_pthread_flags"
+        ;;
+esac
+
+if test x"$acx_pthread_ok" = xno; then
+for flag in $acx_pthread_flags; do
+
+        case $flag in
+                none)
+                AC_MSG_CHECKING([whether pthreads work without any flags])
+                ;;
+
+                -*)
+                AC_MSG_CHECKING([whether pthreads work with $flag])
+                PTHREAD_CFLAGS="$flag"
+                ;;
+
+                pthread-config)
+                AC_CHECK_PROG(acx_pthread_config, pthread-config, yes, no)
+                if test x"$acx_pthread_config" = xno; then continue; fi
+                PTHREAD_CFLAGS="`pthread-config --cflags`"
+                PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
+                ;;
+
+                *)
+                AC_MSG_CHECKING([for the pthreads library -l$flag])
+                PTHREAD_LIBS="-l$flag"
+                ;;
+        esac
+
+        save_LIBS="$LIBS"
+        save_CFLAGS="$CFLAGS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+
+        # Check for various functions.  We must include pthread.h,
+        # since some functions may be macros.  (On the Sequent, we
+        # need a special flag -Kthread to make this header compile.)
+        # We check for pthread_join because it is in -lpthread on IRIX
+        # while pthread_create is in libc.  We check for pthread_attr_init
+        # due to DEC craziness with -lpthreads.  We check for
+        # pthread_cleanup_push because it is one of the few pthread
+        # functions on Solaris that doesn't have a non-functional libc stub.
+        # We try pthread_create on general principles.
+        AC_TRY_LINK([#include <pthread.h>],
+                    [pthread_t th; pthread_join(th, 0);
+                     pthread_attr_init(0); pthread_cleanup_push(0, 0);
+                     pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
+                    [acx_pthread_ok=yes])
+
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+
+        AC_MSG_RESULT($acx_pthread_ok)
+        if test "x$acx_pthread_ok" = xyes; then
+                break;
+        fi
+
+        PTHREAD_LIBS=""
+        PTHREAD_CFLAGS=""
+done
+fi
+
+# Various other checks:
+if test "x$acx_pthread_ok" = xyes; then
+        save_LIBS="$LIBS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        save_CFLAGS="$CFLAGS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+
+        # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
+        AC_MSG_CHECKING([for joinable pthread attribute])
+        attr_name=unknown
+        for attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
+            AC_TRY_LINK([#include <pthread.h>], [int attr=$attr; return attr;],
+                        [attr_name=$attr; break])
+        done
+        AC_MSG_RESULT($attr_name)
+        if test "$attr_name" != PTHREAD_CREATE_JOINABLE; then
+            AC_DEFINE_UNQUOTED([PTHREAD_CREATE_JOINABLE], $attr_name,
+                               [Define to necessary symbol if this constant
+                                uses a non-standard name on your system.])
+        fi
+
+        AC_MSG_CHECKING([if more special flags are required for pthreads])
+        flag=no
+        case "${host_cpu}-${host_os}" in
+            *-aix* | *-freebsd* | *-darwin*) flag="-D_THREAD_SAFE";;
+            *solaris* | *-osf* | *-hpux*) flag="-D_REENTRANT";;
+        esac
+        AC_MSG_RESULT(${flag})
+        if test "x$flag" != xno; then
+            PTHREAD_CFLAGS="$flag $PTHREAD_CFLAGS"
+        fi
+
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+
+        # More AIX lossage: must compile with xlc_r or cc_r
+        if test x"$GCC" != xyes; then
+          AC_CHECK_PROGS(PTHREAD_CC, xlc_r cc_r, ${CC})
+        else
+          PTHREAD_CC=$CC
+        fi
+else
+        PTHREAD_CC="$CC"
+fi
+
+AC_SUBST(PTHREAD_LIBS)
+AC_SUBST(PTHREAD_CFLAGS)
+AC_SUBST(PTHREAD_CC)
+
+# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
+if test x"$acx_pthread_ok" = xyes; then
+        ifelse([$1],,AC_DEFINE([HAVE_PTHREAD],1,[Define if you have POSIX threads libraries and header files.]),[$1])
+        :
+else
+        acx_pthread_ok=no
+        $2
+fi
+AC_LANG_RESTORE
+])dnl ACX_PTHREAD
+
+dnl GUILE_GNU_LD_RELRO
+dnl
+dnl Check whether GNU ld's read-only relocations (the `PT_GNU_RELRO'
+dnl ELF segment header) are supported.  This allows things like
+dnl statically allocated cells (1) to eventually be remapped read-only
+dnl by the loader, and (2) to be identified as pointerless by the
+dnl garbage collector.  Substitute `GNU_LD_FLAGS' with the relevant
+dnl flags.
+AC_DEFUN([GUILE_GNU_LD_RELRO], [
+  AC_MSG_CHECKING([whether the linker understands `-z relro'])
+
+  GNU_LD_FLAGS="-Wl,-z -Wl,relro"
+
+  save_LDFLAGS="$LDFLAGS"
+  LDFLAGS="$LDFLAGS $GNU_LD_FLAGS"
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])],
+    [AC_MSG_RESULT([yes])],
+    [AC_MSG_RESULT([no])
+     GNU_LD_FLAGS=""])
+  LDFLAGS="$save_LDFLAGS"
+
+  AC_SUBST([GNU_LD_FLAGS])
+])
+
+dnl GUILE_THREAD_LOCAL_STORAGE
+dnl
+dnl Check for compiler thread-local storage (TLS) support.
+AC_DEFUN([GUILE_THREAD_LOCAL_STORAGE], [
+  AC_REQUIRE([AC_CANONICAL_HOST])
+
+  AC_CACHE_CHECK([whether the `__thread' storage class is available],
+    [ac_cv_have_thread_storage_class],
+    [dnl On some systems, e.g., NetBSD 5.0 with GCC 4.1, `__thread' is
+     dnl properly compiled but fails to link due to the lack of TLS
+     dnl support in the C library.  Thus we try to link, not just
+     dnl compile.  Unfortunately, this test is not enough, so we
+     dnl explicitly check for known-broken systems.  See
+     dnl http://lists.gnu.org/archive/html/guile-devel/2009-10/msg00138.html
+     dnl for details.
+     dnl
+     dnl Known broken systems includes:
+     dnl   - x86_64-unknown-netbsd5.0.
+     dnl   - x86_64-unknown-netbsd5.1
+     dnl   - sparc-sun-solaris2.8
+     dnl
+     dnl On `x86_64-unknown-freebsd8.0', thread-local storage appears to
+     dnl be reclaimed at the wrong time, leading to a segfault when
+     dnl running `threads.test'.  So disable it.
+     case "$enable_shared--$host_os" in
+       [yes--netbsd[0-5].[0-9]*|yes--solaris2.8|yes--freebsd[0-8]*])
+         ac_cv_have_thread_storage_class="no"
+         ;;
+       *)
+         AC_LINK_IFELSE([AC_LANG_PROGRAM([__thread int tls_integer;],
+                          [tls_integer = 123;])],
+           [ac_cv_have_thread_storage_class="yes"],
+           [ac_cv_have_thread_storage_class="no"])
+         ;;
+     esac])
+
+  if test "x$ac_cv_have_thread_storage_class" = "xyes"; then
+     SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS=1
+  else
+     SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS=0
+  fi
+
+  AC_SUBST([SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS])
+])
+
+dnl GUILE_READLINE
+dnl
+dnl Check all the things needed by `guile-readline', the Readline
+dnl bindings.
+AC_DEFUN([GUILE_READLINE], [
+  for termlib in ncurses curses termcap terminfo termlib pdcurses ; do
+     AC_CHECK_LIB(${termlib}, [tgoto],
+       [READLINE_LIBS="-l${termlib} $READLINE_LIBS"; break])
+  done
+
+  AC_LIB_LINKFLAGS([readline])
+
+  if test "x$LTLIBREADLINE" = "x"; then
+    AC_MSG_WARN([GNU Readline was not found on your system.])
+  else
+    rl_save_LIBS="$LIBS"
+    LIBS="$LIBREADLINE $READLINE_LIBS $LIBS"
+
+    AC_CHECK_FUNCS([siginterrupt rl_clear_signals rl_cleanup_after_signal])
+
+    dnl Check for modern readline naming
+    AC_CHECK_FUNCS([rl_filename_completion_function])
+    AC_CHECK_DECLS([rl_catch_signals, rl_catch_sigwinch], [], [],
+                   [[#include <stdio.h>]
+                    [#include <readline/readline.h>]])
+
+    dnl Check for rl_get_keymap.  We only use this for deciding whether to
+    dnl install paren matching on the Guile command line (when using
+    dnl readline for input), so it's completely optional.
+    AC_CHECK_FUNCS([rl_get_keymap])
+
+    AC_CACHE_CHECK([for rl_getc_function pointer in readline],
+                    ac_cv_var_rl_getc_function,
+                    [AC_TRY_LINK([
+    #include <stdio.h>
+    #include <readline/readline.h>],
+                                 [printf ("%ld", (long) rl_getc_function)],
+                                 [ac_cv_var_rl_getc_function=yes],
+                                 [ac_cv_var_rl_getc_function=no])])
+    if test "${ac_cv_var_rl_getc_function}" = "yes"; then
+      AC_DEFINE([HAVE_RL_GETC_FUNCTION], 1,
+       [Define if your readline library has the rl_getc_function variable.])
+    fi
+
+    if test $ac_cv_var_rl_getc_function = no; then
+      AC_MSG_WARN([*** GNU Readline is too old on your system.])
+      AC_MSG_WARN([*** You need readline version 2.1 or later.])
+      LTLIBREADLINE=""
+      LIBREADLINE=""
     fi
+
+    LIBS="$rl_save_LIBS"
+
+    READLINE_LIBS="$LTLIBREADLINE $READLINE_LIBS"
   fi
+
+  AM_CONDITIONAL([HAVE_READLINE], [test "x$LTLIBREADLINE" != "x"])
+
+  AC_CHECK_FUNCS([strdup])
+
+  AC_SUBST([READLINE_LIBS])
 ])
+
+dnl GUILE_LIBUNISTRING_WITH_ICONV_SUPPORT
+dnl
+dnl Check whether libunistring has iconv support.  When it lacks iconv
+dnl support, `mem_iconveh' returns -1 (ENOSYS) and conversions from one
+dnl codeset to another do not work.
+AC_DEFUN([GUILE_LIBUNISTRING_WITH_ICONV_SUPPORT], [
+  AC_CACHE_CHECK([whether libunistring was built with iconv support],
+    [ac_cv_libunistring_with_iconv_support], [
+     save_LIBS=$LIBS
+     LIBS="$LIBS $LIBUNISTRING"
+     AC_RUN_IFELSE([AC_LANG_SOURCE([[
+       #include <uniconv.h>
+       #include <unistring/iconveh.h>
+       int
+       main (int argc, char *argv[])
+       {
+        size_t result_size;
+        return (NULL == u32_conv_from_encoding ("ASCII", iconveh_question_mark,
+                                                "a", 1,
+                                                NULL, NULL, &result_size));
+       }
+     ]])],
+        [ac_cv_libunistring_with_iconv_support=yes],
+        [ac_cv_libunistring_with_iconv_support=no],
+        [ac_cv_libunistring_with_iconv_support=yes])
+     LIBS=$save_LIBS
+   ])
+])
+
+dnl GUILE_UNISTRING_CONSTANT NAME
+dnl
+dnl Determine the compile-time value of NAME and define/substitute
+dnl `SCM_I_GSC_NAME'.
+AC_DEFUN([GUILE_UNISTRING_CONSTANT], [
+  m4_pushdef([UPPER_CASE_NAME],
+    [m4_translit([$1],[abcdefghijklmnopqrstuvwxyz],
+                  [ABCDEFGHIJKLMNOPQRSTUVWXYZ])])
+
+  AC_CACHE_CHECK([the value of `$1'], [ac_cv_]$1, [
+    AC_COMPUTE_INT([ac_cv_]$1, [$1],
+      [AC_INCLUDES_DEFAULT
+#include <uniconv.h>
+],
+      [AC_MSG_ERROR([failed to determine the value of `$1'])])
+  ])
+
+  [SCM_I_GSC_]UPPER_CASE_NAME="$ac_cv_[]$1"
+  AC_SUBST([SCM_I_GSC_]UPPER_CASE_NAME)
+  m4_popdef([UPPER_CASE_NAME])])
+
+dnl GUILE_UNISTRING_ICONVEH_VALUES
+dnl
+dnl Determine the values of the `iconveh_' libunistring constants.
+AC_DEFUN([GUILE_UNISTRING_ICONVEH_VALUES], [
+  GUILE_UNISTRING_CONSTANT([iconveh_error])
+  GUILE_UNISTRING_CONSTANT([iconveh_question_mark])
+  GUILE_UNISTRING_CONSTANT([iconveh_escape_sequence])
+])
+
+dnl GUILE_CHECK_VERSION
+dnl
+dnl Ensure that $GUILE_FOR_BUILD has the same version as ourselves.
+AC_DEFUN([GUILE_CHECK_VERSION], [
+  if ! "$GUILE_FOR_BUILD" --version > /dev/null 2>&1; then
+     AC_MSG_ERROR([failed to run `$GUILE_FOR_BUILD'])
+  fi
+
+  dnl Use MAJOR.MINOR.MICRO instead of (version) so that developers can
+  dnl freely shoot themselves in the foot by using, say, 2.0.3.80 and
+  dnl 2.0.3.42.
+  AC_CACHE_CHECK([the version of $GUILE_FOR_BUILD],
+    [ac_cv_guile_for_build_version],
+    [ac_cv_guile_for_build_version="`"$GUILE_FOR_BUILD" \
+       -c '(format #t "~a.~a.~a" (major-version) (minor-version) (micro-version))'`"
+    ])
+
+  if test "$ac_cv_guile_for_build_version" != \
+       "$GUILE_MAJOR_VERSION.$GUILE_MINOR_VERSION.$GUILE_MICRO_VERSION"
+  then
+      AC_MSG_ERROR([building Guile $PACKAGE_VERSION but `$GUILE_FOR_BUILD' has version $ac_cv_guile_for_build_version"])
+  fi
+])
+
+dnl GUILE_CHECK_GUILE_FOR_BUILD
+dnl
+dnl When cross-compiling, ensure that $GUILE_FOR_BUILD is suitable.
+AC_DEFUN([GUILE_CHECK_GUILE_FOR_BUILD], [
+  if test "$cross_compiling" = "yes"; then
+    if test "x$GUILE_FOR_BUILD" = "x"; then
+      AC_PATH_PROG([GUILE_FOR_BUILD], [guile], [not-found])
+      if test "$GUILE_FOR_BUILD" = "not-found"; then
+        AC_MSG_ERROR([a native Guile $PACKAGE_VERSION is required to cross-build Guile])
+      fi
+    fi
+    AC_MSG_CHECKING([guile for build])
+    AC_MSG_RESULT([$GUILE_FOR_BUILD])
+
+    dnl Since there is currently no distinction between the run-time
+    dnl search path, %load-path, and the compiler's search path,
+    dnl $GUILE_FOR_BUILD must be a native build of the very same version.
+    GUILE_CHECK_VERSION
+  else
+    GUILE_FOR_BUILD='this-value-will-never-be-used'
+  fi
+
+  AC_ARG_VAR([GUILE_FOR_BUILD], [guile for the build system])
+  AM_SUBST_NOTMAKE([GUILE_FOR_BUILD])
+])
+
+dnl Declare file $1 to be a script that needs configuring,
+dnl and arrange to make it executable in the process.
+AC_DEFUN([GUILE_CONFIG_SCRIPT],[AC_CONFIG_FILES([$1],[chmod +x $1])])