functions: improve cross-compilation guesses for glibc system hosts

Paul and Eric suggested that improving the cross-compilation guesses
for targets that are glibc systems would be welcome here [1][2].

This patch modifies the cross-compilation behaviour of
  AC_FUNC_CHOWN
  AC_FUNC_GETGROUPS
  AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
  AC_FUNC_MALLOC
  AC_FUNC_MMAP
  AC_FUNC_REALLOC
  AC_FUNC_STRCOLL
so that when the target is a glibc system (or, in case of AC_FUNC_MALLOC
and AC_FUNC_REALLOC, any known "good" Unix system), the guess is
"yes it works" rather than "guessing no".

This is important because some of these macros are used in Gnulib, and
in case of "guessing no" Gnulib provides extra workaround code, and
  1) Generally, when targetting embedded systems, code size should be
     minimized,
  2) In [3], unnecessary workaround code will look like a Glibc bug.

This patch also changes the configure output to "guessing yes" or
"guessing no" in a case where the ac_cv_* variable is undocumented.

[1] http://lists.gnu.org/archive/html/bug-gnulib/2012-05/msg00010.html
[2] http://lists.gnu.org/archive/html/bug-gnulib/2012-05/msg00013.html
[3] http://sourceware.org/glibc/wiki/Testing/Gnulib

This patch was tested with the simple configure.ac file
=============== configure.ac ==================
AC_INIT([dummy], [0])
AC_FUNC_CHOWN
AC_FUNC_GETGROUPS
AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
AC_FUNC_MALLOC
AC_FUNC_MMAP
AC_FUNC_REALLOC
AC_FUNC_STRCOLL
AC_OUTPUT
===============================================

* lib/autoconf/functions.m4 (AC_FUNC_CHOWN): Require AC_CANONICAL_HOST.
When cross-compiling to a glibc system, guess yes.
(AC_FUNC_GETGROUPS): Likewise.
(AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK): Likewise.
(AC_FUNC_STRCOLL): Likewise.
(_AC_FUNC_MALLOC_IF): Require AC_CANONICAL_HOST. When cross-compiling
to a know Unix system other than AIX and OSF/1, guess yes.
(_AC_FUNC_REALLOC_IF): Likewise.
(AC_FUNC_MMAP): Require AC_CANONICAL_HOST. When cross-compiling to a
system with a Linux kernel, guess yes.

diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 6f21fd599cd12ee5c98a539f0e0bc4f677ee32b1..97cb7b9b0ed91302bb7aefa5e39e80d500ba078e 100644 (file)
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -423,6 +423,7 @@ AU_ALIAS([AC_ALLOCA], [AC_FUNC_ALLOCA])
 AN_FUNCTION([chown], [AC_FUNC_CHOWN])
 AC_DEFUN([AC_FUNC_CHOWN],
 [AC_REQUIRE([AC_TYPE_UID_T])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
 AC_CHECK_HEADERS(unistd.h)
 AC_CACHE_CHECK([for working chown], ac_cv_func_chown_works,
 [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT
@@ -443,7 +444,12 @@ AC_CACHE_CHECK([for working chown], ac_cv_func_chown_works,
 ]])],
               [ac_cv_func_chown_works=yes],
               [ac_cv_func_chown_works=no],
-              [ac_cv_func_chown_works=no])
+              [case "$host_os" in # ((
+                         # Guess yes on glibc systems.
+                 *-gnu*) ac_cv_func_chown_works=yes ;;
+                         # If we don't know, assume the worst.
+                 *)      ac_cv_func_chown_works=no ;;
+               esac])
 rm -f conftest.chown
 ])
 if test $ac_cv_func_chown_works = yes; then
@@ -625,6 +631,7 @@ AN_FUNCTION([getgroups], [AC_FUNC_GETGROUPS])
 AC_DEFUN([AC_FUNC_GETGROUPS],
 [AC_REQUIRE([AC_TYPE_GETGROUPS])dnl
 AC_REQUIRE([AC_TYPE_SIZE_T])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
 AC_CHECK_FUNC(getgroups)
 
 # If we don't yet have getgroups, see if it's in -lbsd.
@@ -643,15 +650,22 @@ if test $ac_cv_func_getgroups = yes; then
        return getgroups (0, 0) == -1;]])],
                  [ac_cv_func_getgroups_works=yes],
                  [ac_cv_func_getgroups_works=no],
-                 [ac_cv_func_getgroups_works=no])
+                 [case "$host_os" in # ((
+                            # Guess yes on glibc systems.
+                    *-gnu*) ac_cv_func_getgroups_works="guessing yes" ;;
+                            # If we don't know, assume the worst.
+                    *)      ac_cv_func_getgroups_works="guessing no" ;;
+                  esac])
    ])
 else
   ac_cv_func_getgroups_works=no
 fi
-if test $ac_cv_func_getgroups_works = yes; then
-  AC_DEFINE(HAVE_GETGROUPS, 1,
-           [Define to 1 if your system has a working `getgroups' function.])
-fi
+case "$ac_cv_func_getgroups_works" in
+  *yes)
+    AC_DEFINE(HAVE_GETGROUPS, 1,
+             [Define to 1 if your system has a working `getgroups' function.])
+    ;;
+esac
 LIBS=$ac_save_LIBS
 ])# AC_FUNC_GETGROUPS
 
@@ -847,7 +861,8 @@ fi
 # calls lstat a second time when necessary.
 AN_FUNCTION([lstat], [AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK])
 AC_DEFUN([AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK],
-[AC_CACHE_CHECK(
+[AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
+AC_CACHE_CHECK(
        [whether lstat correctly handles trailing slash],
        [ac_cv_func_lstat_dereferences_slashed_symlink],
 [rm -f conftest.sym conftest.file
@@ -861,7 +876,12 @@ if test "$as_ln_s" = "ln -s" && ln -s conftest.file conftest.sym; then
      return lstat ("conftest.sym/", &sbuf) == 0;])],
                [ac_cv_func_lstat_dereferences_slashed_symlink=yes],
                [ac_cv_func_lstat_dereferences_slashed_symlink=no],
-               [ac_cv_func_lstat_dereferences_slashed_symlink=no])
+               [case "$host_os" in # ((
+                          # Guess yes on glibc systems.
+                  *-gnu*) ac_cv_func_lstat_dereferences_slashed_symlink=yes ;;
+                          # If we don't know, assume the worst.
+                  *)      ac_cv_func_lstat_dereferences_slashed_symlink=no ;;
+                esac])
 else
   # If the `ln -s' command failed, then we probably don't even
   # have an lstat function.
@@ -886,6 +906,7 @@ fi
 # If `malloc (0)' properly handled, run IF-WORKS, otherwise, IF-NOT.
 AC_DEFUN([_AC_FUNC_MALLOC_IF],
 [AC_REQUIRE([AC_HEADER_STDC])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
 AC_CHECK_HEADERS(stdlib.h)
 AC_CACHE_CHECK([for GNU libc compatible malloc], ac_cv_func_malloc_0_nonnull,
 [AC_RUN_IFELSE(
@@ -899,7 +920,14 @@ char *malloc ();
                 [return ! malloc (0);])],
               [ac_cv_func_malloc_0_nonnull=yes],
               [ac_cv_func_malloc_0_nonnull=no],
-              [ac_cv_func_malloc_0_nonnull=no])])
+              [case "$host_os" in # ((
+                 # Guess yes on platforms where we know the result.
+                 *-gnu* | freebsd* | netbsd* | openbsd* \
+                 | hpux* | solaris* | cygwin* | mingw*)
+                   ac_cv_func_malloc_0_nonnull=yes ;;
+                 # If we don't know, assume the worst.
+                 *) ac_cv_func_malloc_0_nonnull=no ;;
+               esac])])
 AS_IF([test $ac_cv_func_malloc_0_nonnull = yes], [$1], [$2])
 ])# _AC_FUNC_MALLOC_IF
 
@@ -1199,7 +1227,8 @@ AU_ALIAS([AM_FUNC_MKTIME], [AC_FUNC_MKTIME])
 # ------------
 AN_FUNCTION([mmap], [AC_FUNC_MMAP])
 AC_DEFUN([AC_FUNC_MMAP],
-[AC_CHECK_HEADERS_ONCE([stdlib.h unistd.h sys/param.h])
+[AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
+AC_CHECK_HEADERS_ONCE([stdlib.h unistd.h sys/param.h])
 AC_CHECK_FUNCS([getpagesize])
 AC_CACHE_CHECK([for working mmap], [ac_cv_func_mmap_fixed_mapped],
 [AC_RUN_IFELSE([AC_LANG_SOURCE([AC_INCLUDES_DEFAULT]
@@ -1340,7 +1369,12 @@ main ()
 }]])],
               [ac_cv_func_mmap_fixed_mapped=yes],
               [ac_cv_func_mmap_fixed_mapped=no],
-              [ac_cv_func_mmap_fixed_mapped=no])])
+              [case "$host_os" in # ((
+                         # Guess yes on platforms where we know the result.
+                 linux*) ac_cv_func_mmap_fixed_mapped=yes ;;
+                         # If we don't know, assume the worst.
+                 *)      ac_cv_func_mmap_fixed_mapped=no ;;
+               esac])])
 if test $ac_cv_func_mmap_fixed_mapped = yes; then
   AC_DEFINE([HAVE_MMAP], [1],
            [Define to 1 if you have a working `mmap' system call.])
@@ -1391,6 +1425,7 @@ AU_ALIAS([AM_FUNC_OBSTACK], [AC_FUNC_OBSTACK])
 # If `realloc (0, 0)' is properly handled, run IF-WORKS, otherwise, IF-NOT.
 AC_DEFUN([_AC_FUNC_REALLOC_IF],
 [AC_REQUIRE([AC_HEADER_STDC])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
 AC_CHECK_HEADERS(stdlib.h)
 AC_CACHE_CHECK([for GNU libc compatible realloc], ac_cv_func_realloc_0_nonnull,
 [AC_RUN_IFELSE(
@@ -1404,7 +1439,14 @@ char *realloc ();
                 [return ! realloc (0, 0);])],
               [ac_cv_func_realloc_0_nonnull=yes],
               [ac_cv_func_realloc_0_nonnull=no],
-              [ac_cv_func_realloc_0_nonnull=no])])
+              [case "$host_os" in # ((
+                 # Guess yes on platforms where we know the result.
+                 *-gnu* | freebsd* | netbsd* | openbsd* \
+                 | hpux* | solaris* | cygwin* | mingw*)
+                   ac_cv_func_realloc_0_nonnull=yes ;;
+                 # If we don't know, assume the worst.
+                 *) ac_cv_func_realloc_0_nonnull=no ;;
+               esac])])
 AS_IF([test $ac_cv_func_realloc_0_nonnull = yes], [$1], [$2])
 ])# AC_FUNC_REALLOC
 
@@ -1723,14 +1765,20 @@ AU_ALIAS([AC_SETVBUF_REVERSED], [AC_FUNC_SETVBUF_REVERSED])
 # ---------------
 AN_FUNCTION([strcoll], [AC_FUNC_STRCOLL])
 AC_DEFUN([AC_FUNC_STRCOLL],
-[AC_CACHE_CHECK(for working strcoll, ac_cv_func_strcoll_works,
+[AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
+AC_CACHE_CHECK(for working strcoll, ac_cv_func_strcoll_works,
 [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT],
   [[return (strcoll ("abc", "def") >= 0 ||
         strcoll ("ABC", "DEF") >= 0 ||
         strcoll ("123", "456") >= 0)]])],
               ac_cv_func_strcoll_works=yes,
               ac_cv_func_strcoll_works=no,
-              ac_cv_func_strcoll_works=no)])
+              [case "$host_os" in # ((
+                         # Guess yes on glibc systems.
+                 *-gnu*) ac_cv_func_strcoll_works=yes ;;
+                         # If we don't know, assume the worst.
+                 *)      ac_cv_func_strcoll_works=no ;;
+               esac])])
 if test $ac_cv_func_strcoll_works = yes; then
   AC_DEFINE(HAVE_STRCOLL, 1,
            [Define to 1 if you have the `strcoll' function and it is properly