Port AC_FUNC_MMAP to more-modern systems

* lib/autoconf/functions.m4 (AC_FUNC_MMAP): Don’t call
getpagesize, as it’s tricky to configure, modern POSIX doesn’t
require it, and calling it without including <unistd.h> provokes a
compile-time error on modern systems.  Instead, rework the test
to not need getpagesize.  Add a FIXME comment for unnecessary
tests; I don't want to remove them now as we're too close to
a release.  Remove long-obsolete comment about GNU grep.

1 files changed, 5 insertions, 39 deletions

diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 499e4c02..5a0f0185 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -1283,6 +1283,7 @@ AU_ALIAS([AM_FUNC_MKTIME], [AC_FUNC_MKTIME])
 AN_FUNCTION([mmap], [AC_FUNC_MMAP])
 AC_DEFUN([AC_FUNC_MMAP],
 [AC_REQUIRE([AC_CANONICAL_HOST])dnl for cross-compiles
+dnl FIXME: Remove the unnecessary checks for unistd.h, sys/param.h, getpagesize.
 AC_CHECK_HEADERS_ONCE([unistd.h sys/param.h])
 AC_CHECK_FUNCS_ONCE([getpagesize])
 AC_CACHE_CHECK([for working mmap], [ac_cv_func_mmap_fixed_mapped],
@@ -1305,48 +1306,11 @@ AC_CACHE_CHECK([for working mmap], [ac_cv_func_mmap_fixed_mapped],
    VM page cache was not coherent with the file system buffer cache
    like early versions of FreeBSD and possibly contemporary NetBSD.)
    For shared mappings, we should conversely verify that changes get
-   propagated back to all the places they're supposed to be.
-
-   Grep wants private fixed already mapped.
-   The main things grep needs to know about mmap are:
-   * does it exist and is it safe to write into the mmap'd area
-   * how to use it (BSD variants)  */
+   propagated back to all the places they're supposed to be.  */
 
 #include <fcntl.h>
 #include <sys/mman.h>
 
-/* This mess was copied from the GNU getpagesize.h.  */
-#ifndef HAVE_GETPAGESIZE
-# ifdef _SC_PAGESIZE
-#  define getpagesize() sysconf(_SC_PAGESIZE)
-# else /* no _SC_PAGESIZE */
-#  ifdef HAVE_SYS_PARAM_H
-#   include <sys/param.h>
-#   ifdef EXEC_PAGESIZE
-#    define getpagesize() EXEC_PAGESIZE
-#   else /* no EXEC_PAGESIZE */
-#    ifdef NBPG
-#     define getpagesize() NBPG * CLSIZE
-#     ifndef CLSIZE
-#      define CLSIZE 1
-#     endif /* no CLSIZE */
-#    else /* no NBPG */
-#     ifdef NBPC
-#      define getpagesize() NBPC
-#     else /* no NBPC */
-#      ifdef PAGESIZE
-#       define getpagesize() PAGESIZE
-#      endif /* PAGESIZE */
-#     endif /* no NBPC */
-#    endif /* no NBPG */
-#   endif /* no EXEC_PAGESIZE */
-#  else /* no HAVE_SYS_PARAM_H */
-#   define getpagesize() 8192	/* punt totally */
-#  endif /* no HAVE_SYS_PARAM_H */
-# endif /* no _SC_PAGESIZE */
-
-#endif /* no HAVE_GETPAGESIZE */
-
 int
 main (void)
 {
@@ -1355,7 +1319,9 @@ main (void)
   int i, pagesize;
   int fd, fd2;
 
-  pagesize = getpagesize ();
+  /* The "page size" need not equal the system page size,
+     and need not even be a power of 2.  */
+  pagesize = 8192;
 
   /* First, make a file with some known garbage in it. */
   data = (char *) malloc (pagesize);