diff --git a/src/configure b/src/configure
index 2bbca83030..0d8f713aa4 100755
--- a/src/configure
+++ b/src/configure
@@ -5021,6 +5021,75 @@ _ACEOF
 
 
 
+ msg="for stack direction"
+echo "$as_me:$LINENO: checking $msg" >&5
+echo $ECHO_N "checking $msg... $ECHO_C" >&6
+if test "$cross_compiling" = yes; then
+  stack_direction=unknown
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+int grows_down_p(int n, void *cmp) {
+     if (!cmp)
+       return grows_down_p(10, &cmp);
+     else if (!n)
+       return ((unsigned long)&cmp < (unsigned long)cmp);
+     else
+       return grows_down_p(n - 1, cmp);
+   }
+   int main() {
+      return grows_down_p();
+   }
+_ACEOF
+rm -f conftest$ac_exeext
+if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && { ac_try='./conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  stack_direction=up
+else
+  echo "$as_me: program exited with status $ac_status" >&5
+echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+( exit $ac_status )
+stack_direction=down
+fi
+rm -f core *.core gmon.out bb.out conftest$ac_exeext conftest.$ac_objext conftest.$ac_ext
+fi
+echo "$as_me:$LINENO: result: $stack_direction" >&5
+echo "${ECHO_T}$stack_direction" >&6
+
+if test "${stack_direction}" = "uknown" ; then
+  echo configure: cannot determine stack direction
+  exit 1
+fi
+
+if test "${stack_direction}" = "up" ; then
+
+cat >>confdefs.h <<\_ACEOF
+#define STACK_DIRECTION 1
+_ACEOF
+
+fi
+if test "${stack_direction}" = "down" ; then
+
+cat >>confdefs.h <<\_ACEOF
+#define STACK_DIRECTION -1
+_ACEOF
+
+fi
+
 ###### Some flags imply other flags #######
 
 if test "${enable_smalloskit}" = "yes" ; then
diff --git a/src/mzscheme/configure.ac b/src/mzscheme/configure.ac
index 0d6fab2cea..d7c4746b66 100644
--- a/src/mzscheme/configure.ac
+++ b/src/mzscheme/configure.ac
@@ -89,6 +89,34 @@ AC_CHECK_SIZEOF(int)
 AC_CHECK_SIZEOF(long)
 AC_CHECK_SIZEOF(long long)
 
+[ msg="for stack direction" ]
+AC_MSG_CHECKING($msg)
+AC_TRY_RUN(
+   int grows_down_p(int n, void *cmp) {
+     if (!cmp)
+       return grows_down_p(10, &cmp);
+     else if (!n)
+       return ((unsigned long)&cmp < (unsigned long)cmp);
+     else
+       return grows_down_p(n - 1, cmp);
+   }
+   int main() {
+      return grows_down_p();
+   }, stack_direction=up, stack_direction=down, stack_direction=unknown)
+AC_MSG_RESULT($stack_direction) 
+
+if test "${stack_direction}" = "uknown" ; then
+  echo configure: cannot determine stack direction
+  exit 1
+fi
+
+if test "${stack_direction}" = "up" ; then
+  AC_DEFINE(STACK_DIRECTION,1,[Stack direction up])
+fi
+if test "${stack_direction}" = "down" ; then
+  AC_DEFINE(STACK_DIRECTION,-1,[Stack direction down])
+fi
+
 ###### Some flags imply other flags #######
 
 if test "${enable_smalloskit}" = "yes" ; then
diff --git a/src/mzscheme/gc2/Makefile.in b/src/mzscheme/gc2/Makefile.in
index 2e9121fcdf..909cb66ef9 100644
--- a/src/mzscheme/gc2/Makefile.in
+++ b/src/mzscheme/gc2/Makefile.in
@@ -288,8 +288,9 @@ main.@LTO@: $(XSRCDIR)/main.c
 	$(CC) $(CFLAGS) -c $(XSRCDIR)/main.c -o main.@LTO@
 
 gc2.@LTO@: $(srcdir)/gc2.c $(srcdir)/newgc.c $(srcdir)/compact.c $(srcdir)/newgc.c $(srcdir)/gc2.h \
-       $(srcdir)/vm_osx.c $(srcdir)/vm_mmap.c $(srcdir)/vm_osk.c $(srcdir)/alloc_cache.c $(srcdir)/my_qsort.c \
-       $(srcdir)/page_range.c $(srcdir)/protect_range.c $(srcdir)/../utils/splay.c \
+       $(srcdir)/vm_osx.c $(srcdir)/vm_mmap.c $(srcdir)/vm_osk.c $(srcdir)/alloc_cache.c \
+       $(srcdir)/page_range.c $(srcdir)/protect_range.c $(srcdir)/var_stack.c $(srcdir)/stack_comp.c \
+       $(srcdir)/../utils/splay.c $(srcdir)/my_qsort.c \
        $(srcdir)/weak.c $(srcdir)/fnls.c $(srcdir)/../include/scheme.h $(srcdir)/../src/schpriv.h
 	$(CC) $(CFLAGS) -c $(srcdir)/gc2.c -o gc2.@LTO@
 
diff --git a/src/mzscheme/gc2/compact.c b/src/mzscheme/gc2/compact.c
index 78080cf856..7b941bf4dd 100644
--- a/src/mzscheme/gc2/compact.c
+++ b/src/mzscheme/gc2/compact.c
@@ -89,8 +89,8 @@ typedef short Type_Tag;
 /* Debugging and performance tools: */
 #define TIME 0
 #define SEARCH 0
-#define CHECKS 0
-#define CHECK_STACK_PTRS 0
+#define CHECKS 1
+#define CHECK_STACK_PTRS 1
 #define NOISY 0
 #define MARK_STATS 0
 #define ALLOC_GC_PHASE 0
@@ -2720,124 +2720,27 @@ static int stack_depth;
 static int record_stack_source = 0;
 #endif
 
-void GC_mark_variable_stack(void **var_stack,
-			    long delta,
-			    void *limit)
-{
-  long size, count;
-  void ***p, **a;
+#include "stack_comp.c"
 
-#if TIME
-  stack_depth = 0;
-#endif
-
-  while (var_stack) {
-    var_stack = (void **)((char *)var_stack + delta);
-    if (var_stack == limit)
-      return;
-
-    size = *(long *)(var_stack + 1);
-
-#if CHECKS
-    oo_var_stack = o_var_stack;
-    o_var_stack = var_stack;
-#endif
-
-    p = (void ***)(var_stack + 2);
-    
-    while (size--) {
-      a = *p;
-      if (!a) {
-	/* Array */
-	count = ((long *)p)[2];
-	a = ((void ***)p)[1];
-	p += 2;
-	size -= 2;
-	a = (void **)((char *)a + delta);
-	while (count--) {
+#define GC_X_variable_stack GC_mark_variable_stack
 #if RECORD_MARK_SRC
-	  if (record_stack_source) {
-	    mark_src = a;
-	    mark_type = MTYPE_STACK;
-	  }
+# define X_source(p) if (record_stack_source) { mark_src = p; mark_type = MTYPE_STACK; }
+#else
+# define X_source(p) /* */
 #endif
-	  gcMARK(*a);
-	  a++;
-	}
-      } else {
-	a = (void **)((char *)a + delta);
-#if RECORD_MARK_SRC
-	if (record_stack_source) {
-	  mark_src = a;
-	  mark_type = MTYPE_STACK;
-	}
-#endif
-	gcMARK(*a);
-      }
-      p++;
-    }
+#define gcX(p) gcMARK(p)
+#include "var_stack.c"
+#undef GC_X_variable_stack
+#undef gcX
+#undef X_source
 
-#if 0
-    if (*var_stack && ((unsigned long)*var_stack < (unsigned long)var_stack)) {
-      GCPRINT(GCOUTF, "bad %d\n", stack_depth);
-      CRASH(32);
-    }
-#endif
-
-    var_stack = *var_stack;
-
-#if TIME
-    stack_depth++;
-#endif
-  }
-}
-
-void GC_fixup_variable_stack(void **var_stack,
-			     long delta,
-			     void *limit)
-{
-  long size, count;
-  void ***p, **a;
-
-#if TIME
-  stack_depth = 0;
-#endif
-
-  while (var_stack) {
-    var_stack = (void **)((char *)var_stack + delta);
-    if (var_stack == limit)
-      return;
-
-    size = *(long *)(var_stack + 1);
-
-    p = (void ***)(var_stack + 2);
-    
-    while (size--) {
-      a = *p;
-      if (!a) {
-	/* Array */
-	count = ((long *)p)[2];
-	a = ((void ***)p)[1];
-	p += 2;
-	size -= 2;
-	a = (void **)((char *)a + delta);
-	while (count--) {
-	  gcFIXUP(*a);
-	  a++;
-	}
-      } else {
-	a = (void **)((char *)a + delta);
-	gcFIXUP(*a);
-      }
-      p++;
-    }
-
-    var_stack = *var_stack;
-#if TIME
-    stack_depth++;
-#endif
-  }
-}
+#define GC_X_variable_stack GC_fixup_variable_stack
+#define gcX(p) gcFIXUP(p)
+#define X_source(p) /* */
+#include "var_stack.c"
+#undef GC_X_variable_stack
+#undef gcX
+#undef X_source
 
 #if CHECKS
 # if CHECK_STACK_PTRS
@@ -2899,6 +2802,11 @@ void GC_check_variable_stack()
     if (*var_stack && ((unsigned long)*var_stack <= (unsigned long)var_stack))
       CRASH(33);
 # endif
+       
+    size = *(long *)(var_stack + 1);
+
+    if (var_stack + size + 2 == limit)
+      return;
 
 # if CHECK_STACK_PTRS
     size = *(long *)(var_stack + 1);
diff --git a/src/mzscheme/gc2/newgc.c b/src/mzscheme/gc2/newgc.c
index 3ad4e6baa6..e4106b3ba5 100644
--- a/src/mzscheme/gc2/newgc.c
+++ b/src/mzscheme/gc2/newgc.c
@@ -486,6 +486,8 @@ void *GC_malloc_one_small_tagged(size_t sizeb)
 {
   unsigned long newsize;
 
+  return GC_malloc_one_tagged(sizeb);
+
   sizeb += WORD_SIZE;
   sizeb = ALIGN_BYTES_SIZE(sizeb);
   newsize = gen0_alloc_page->size + sizeb;
@@ -805,114 +807,27 @@ unsigned long GC_get_stack_base()
   return stack_base;
 }
 
-#define traverse_stack(var_stack, delta, limit, operation) {          \
-    long size, count;                                                 \
-    void ***p, **a;                                                   \
-                                                                      \
-    while(var_stack) {                                                \
-      var_stack = (void **)((char *)var_stack + delta);               \
-      if(var_stack == limit) return;                                  \
-                                                                      \
-      size = *(long*)(var_stack + 1); p = (void***)(var_stack + 2);   \
-      while(size--) {                                                 \
-        a = *p;                                                       \
-        if(!a) {                                                      \
-          count = ((long *)p)[2]; a = ((void***)p)[1];                \
-          p += 2; size -= 2; a = (void**)((char *)a + delta);         \
-          while(count--) { operation(*a); a++; }                      \
-        } else {                                                      \
-          a = (void**)((char *)a + delta); operation(*a);             \
-        }                                                             \
-        p++;                                                          \
-      }                                                               \
-      var_stack = *var_stack;                                         \
-    }                                                                 \
-  }
-
-
 #define gc_stack_base ((void*)(GC_get_thread_stack_base               \
                                ? GC_get_thread_stack_base()           \
                                : (unsigned long)stack_base)) 
 
-/* these names are fixed by the gc2 spec; which is a bit unfortunate */
-void GC_mark_variable_stack(void **var_stack, long delta, void *limit) 
-{
-  long size, count;
-  void ***p, **a;
+#include "stack_comp.c"
 
-  while (var_stack) {
-    var_stack = (void **)((char *)var_stack + delta);
-    if (var_stack == limit)
-      return;
+#define GC_X_variable_stack GC_mark_variable_stack
+#define gcX(p) gcMARK(p)
+#define X_source(p) set_backtrace_source(p, BT_STACK)
+#include "var_stack.c"
+#undef GC_X_variable_stack
+#undef gcX
+#undef X_source
 
-    size = *(long *)(var_stack + 1);
-    p = (void ***)(var_stack + 2);
-    
-    while (size--) {
-      a = *p;
-      if (!a) {
-	/* Array */
-	count = ((long *)p)[2];
-	a = ((void ***)p)[1];
-	p += 2;
-	size -= 2;
-	a = (void **)((char *)a + delta);
-	while (count--) {
-	  set_backtrace_source(a, BT_STACK);
-	  gcMARK(*a);
-	  a++;
-	}
-      } else {
-	a = (void **)((char *)a + delta);
-	set_backtrace_source(a, BT_STACK);
-	gcMARK(*a);
-      }
-      p++;
-    }
-
-    var_stack = *var_stack;
-  }
-/*   traverse_stack(var_stack, delta, limit, gcMARK); */
-}
-
-void GC_fixup_variable_stack(void **var_stack, long delta, void *limit) 
-{
-  long size, count;
-  void ***p, **a;
-
-  while (var_stack) {
-    var_stack = (void **)((char *)var_stack + delta);
-    if (var_stack == limit)
-      return;
-
-    size = *(long *)(var_stack + 1);
-
-    p = (void ***)(var_stack + 2);
-    
-    while (size--) {
-      a = *p;
-      if (!a) {
-	/* Array */
-	count = ((long *)p)[2];
-	a = ((void ***)p)[1];
-	p += 2;
-	size -= 2;
-	a = (void **)((char *)a + delta);
-	while (count--) {
-	  gcFIXUP(*a);
-	  a++;
-	}
-      } else {
-	a = (void **)((char *)a + delta);
-	gcFIXUP(*a);
-      }
-      p++;
-    }
-
-    var_stack = *var_stack;
-  }
-/*   traverse_stack(var_stack, delta, limit, gcFIXUP); */
-} 
+#define GC_X_variable_stack GC_fixup_variable_stack
+#define gcX(p) gcFIXUP(p)
+#define X_source(p) /* */
+#include "var_stack.c"
+#undef GC_X_variable_stack
+#undef gcX
+#undef X_source
 
 /*****************************************************************************/
 /* Routines for root sets                                                    */
@@ -1795,7 +1710,7 @@ int GC_set_account_hook(int type, void *c1, unsigned long b, void *c2)
 /* administration / initialization                                           */
 /*****************************************************************************/
 
-static int generations_available = 1;
+static int generations_available = 0;
 
 void designate_modified(void *p)
 {
diff --git a/src/mzscheme/gc2/stack_comp.c b/src/mzscheme/gc2/stack_comp.c
new file mode 100644
index 0000000000..efe09699b1
--- /dev/null
+++ b/src/mzscheme/gc2/stack_comp.c
@@ -0,0 +1,7 @@
+
+#include "mzconfig.h"
+#if STACK_DIRECTION > 0
+# define SHALLOWER_STACK_ADDRESS(a, b) ((unsigned long)a > (unsigned long)b)
+#else
+# define SHALLOWER_STACK_ADDRESS(a, b) ((unsigned long)a < (unsigned long)b)
+#endif
diff --git a/src/mzscheme/gc2/var_stack.c b/src/mzscheme/gc2/var_stack.c
new file mode 100644
index 0000000000..101bafde63
--- /dev/null
+++ b/src/mzscheme/gc2/var_stack.c
@@ -0,0 +1,84 @@
+
+void GC_X_variable_stack(void **var_stack, long delta, void *limit) 
+{
+  long size, count;
+  void ***p, **a;
+
+#if TIME
+  stack_depth = 0;
+#endif
+
+  while (var_stack) {
+    var_stack = (void **)((char *)var_stack + delta);
+
+    size = *(long *)(var_stack + 1);
+    p = (void ***)(var_stack + 2);
+
+#if CHECKS
+    oo_var_stack = o_var_stack;
+    o_var_stack = var_stack;
+#endif
+
+    if ((var_stack == limit)
+	|| (var_stack + size + 2 == limit)) {
+      /* Last frame: need to X things that are shallower than the
+	 limit: */
+     
+      while (size--) {
+	a = *p;
+	if (!a) {
+	  /* Array */
+	  count = ((long *)p)[2];
+	  a = ((void ***)p)[1];
+	  p += 2;
+	  size -= 2;
+	  a = (void **)((char *)a + delta);
+	  if (SHALLOWER_STACK_ADDRESS(a, limit)) {
+	    while (count--) {
+	      X_source(a);
+	      gcX(*a);
+	      a++;
+	    }
+	  }
+	} else {
+	  a = (void **)((char *)a + delta);
+	  if (SHALLOWER_STACK_ADDRESS(a, limit)) {
+	    X_source(a);
+	    gcX(*a);
+	  }
+	}
+	p++;
+      }
+
+      return;
+    }
+
+    while (size--) {
+      a = *p;
+      if (!a) {
+	/* Array */
+	count = ((long *)p)[2];
+	a = ((void ***)p)[1];
+	p += 2;
+	size -= 2;
+	a = (void **)((char *)a + delta);
+	while (count--) {
+	  X_source(a);
+	  gcX(*a);
+	  a++;
+	}
+      } else {
+	a = (void **)((char *)a + delta);
+	X_source(a);
+	gcX(*a);
+      }
+      p++;
+    }
+
+    var_stack = *var_stack;
+
+#if TIME
+    stack_depth++;
+#endif
+  }
+}
diff --git a/src/mzscheme/mzconfig.h.in b/src/mzscheme/mzconfig.h.in
index 6d192bdaad..85308ae2dd 100644
--- a/src/mzscheme/mzconfig.h.in
+++ b/src/mzscheme/mzconfig.h.in
@@ -1,6 +1,9 @@
 
 /* This file contains information that was gathered by the configure script. */
 
+#ifndef __MZSCHEME_CONFIGURATION_INFO__
+#define __MZSCHEME_CONFIGURATION_INFO__
+
 
 /* The size of a `char', as computed by sizeof. */
 #undef SIZEOF_CHAR
@@ -17,9 +20,14 @@
 /* The size of a `long long', as computed by sizeof. */
 #undef SIZEOF_LONG_LONG
 
+/* Direction of stack growth: 1 = up, -1 = down, 0 = unknown */
+#undef STACK_DIRECTION
 
 /* whether nl_langinfo works */
 #undef HAVE_CODESET
 
 /* whether getaddrinfo works */
 #undef HAVE_GETADDRINFO
+
+
+#endif
diff --git a/src/mzscheme/sconfig.h b/src/mzscheme/sconfig.h
index 8f5ca2260f..fc9779cbdd 100644
--- a/src/mzscheme/sconfig.h
+++ b/src/mzscheme/sconfig.h
@@ -27,7 +27,6 @@
 
 # define SYSTEM_TYPE_NAME "oskit"
 
-# define STACK_GROWS_DOWN
 # define DO_STACK_CHECK
 # ifndef OSKIT_TEST
 #  define OSKIT_FIXED_STACK_BOUNDS
@@ -83,7 +82,6 @@
 
 # include "uconfig.h"
 
-# define STACK_GROWS_DOWN
 # ifndef i386
 #  define SCHEME_BIG_ENDIAN
 # endif
@@ -138,7 +136,6 @@
 # include "uconfig.h"
 # undef USE_FCHDIR
 
-# define STACK_GROWS_DOWN
 # define SCHEME_BIG_ENDIAN
 # define UNIX_LIMIT_STACK 33554944
 
@@ -209,10 +206,7 @@
 # endif
 
 # if defined(__hppa__)
-#  define STACK_GROWS_UP
 #  define SIXTY_FOUR_BIT_INTEGERS
-# else
-#  define STACK_GROWS_DOWN
 # endif
 
 # define USE_IEEE_FP_PREDS
@@ -254,8 +248,6 @@
 # undef HAS_STANDARD_IOB
 # define HAS_BSD_IOB
 
-# define STACK_GROWS_DOWN
-
 #ifndef __ELF__
 # define UNDERSCORE_DYNLOAD_SYMBOL_PREFIX
 #endif
@@ -296,8 +288,6 @@
 
 # define HAS_BSD_IOB
 
-# define STACK_GROWS_DOWN
-
 #ifndef __ELF__
 # define UNDERSCORE_DYNLOAD_SYMBOL_PREFIX
 #endif
@@ -331,8 +321,6 @@
 
 # define HAS_BSD_IOB
 
-# define STACK_GROWS_DOWN
-
 # ifdef FREEBSD_VERSION_2x
 #  define UNDERSCORE_DYNLOAD_SYMBOL_PREFIX
 # endif
@@ -367,7 +355,6 @@
 
 # include "uconfig.h"
 
-# define STACK_GROWS_DOWN
 # define SCHEME_BIG_ENDIAN
 
 # define DIRENT_NO_NAMLEN
@@ -402,7 +389,6 @@
 
 # define DIRENT_NO_NAMLEN
 
-# define STACK_GROWS_DOWN
 # define SCHEME_BIG_ENDIAN
 
 # define NO_USLEEP
@@ -420,8 +406,6 @@
 
 # include "uconfig.h"
 
-# define STACK_GROWS_DOWN
-
 # define SIXTY_FOUR_BIT_INTEGERS
 
 # define ALPHA_CONTROL_FP
@@ -441,7 +425,6 @@
 
 # include "uconfig.h"
 
-# define STACK_GROWS_UP
 # define SCHEME_BIG_ENDIAN
 
 # define SOME_FDS_ARE_NOT_SELECTABLE
@@ -480,8 +463,6 @@
 
 # define HAS_SCO_IOB
 
-# define STACK_GROWS_DOWN
-
 # define USE_SCO_IEEE_FP_PREDS
 # define USE_EXPLICT_FP_FORM_CHECK
 # define USE_FCNTL_O_NONBLOCK
@@ -522,7 +503,6 @@
 # define GETENV_FUNCTION
 # define DIR_FUNCTION
 
-# define STACK_GROWS_DOWN
 # define DO_STACK_CHECK
 # define WINDOWS_FIND_STACK_BOUNDS
 
@@ -628,7 +608,6 @@
 
 # define USE_DIVIDE_MAKE_INFINITY
 
-# define STACK_GROWS_DOWN
 # define DO_STACK_CHECK
 # define WINDOWS_FIND_STACK_BOUNDS
 
@@ -670,7 +649,6 @@
 # define SYSTEM_TYPE_NAME "macosx"
 #endif
 
-# define STACK_GROWS_DOWN
 #ifdef __POWERPC__
 # define SCHEME_BIG_ENDIAN
 #endif
@@ -713,7 +691,6 @@
 
 # include "uconfig.h"
 
-# define STACK_GROWS_DOWN
 # define USE_MAP_ANON
 
 # define USE_DYNAMIC_FDSET_SIZE
@@ -769,7 +746,6 @@
 #  define LINK_EXTENSIONS_BY_TABLE
 # endif
 
-# define STACK_GROWS_DOWN
 # define SCHEME_BIG_ENDIAN
 
 # define DO_STACK_CHECK
@@ -827,8 +803,6 @@
 # define GETENV_FUNCTION
 # define DIR_FUNCTION
 
-# define STACK_GROWS_DOWN
-
 # define DO_STACK_CHECK
 # define USE_STACKAVAIL
 # define STACK_SAFETY_MARGIN 15000
@@ -863,7 +837,6 @@
 # define NO_USER_BREAK_HANDLER
 # define NO_USLEEP
 
-# define STACK_GROWS_DOWN
 # define SCHEME_BIG_ENDIAN
 
 # define DO_STACK_CHECK
@@ -1249,14 +1222,6 @@
 # define UNIX_FIND_STACK_BOUNDS
 # define STACK_SAFETY_MARGIN 50000
 
- /* STACK_GROWS_UP means that deeper stack values have higher
-     numbered addresses.
-    STACK_GROWS_DOWN means that deeper stack values have lower
-     numbered addresses. This is usually the case (Sparc and
-     Intel platforms, for example, use this).
-    Use only one or none of these. (It's faster if you know which
-     one applies, but it can also be figured it out dynamically.) */
-
  /* DO_STACK_CHECK checks for stack overflow during execution.
      Requires either UNIX_FIND_STACK_BOUNDS, USE_STACKAVAIL,
      MACOS_FIND_STACK_BOUNDS, or ASSUME_FIXED_STACK_SIZE. */
diff --git a/src/mzscheme/src/eval.c b/src/mzscheme/src/eval.c
index 03797cb5ac..0ad32c202a 100644
--- a/src/mzscheme/src/eval.c
+++ b/src/mzscheme/src/eval.c
@@ -135,8 +135,6 @@ Scheme_Object *scheme_multiple_values;
 
 volatile int scheme_fuel_counter;
 
-int scheme_stack_grows_up;
-
 int scheme_startup_use_jit = 1;
 void scheme_set_startup_use_jit(int v) { scheme_startup_use_jit =  v; }
 
@@ -540,17 +538,17 @@ scheme_handle_stack_overflow(Scheme_Object *(*k)(void))
 void scheme_init_stack_check()
      /* Finds the C stack limit --- platform-specific. */
 {
-  int *v;
+  int *v, stack_grows_up;
   unsigned long deeper;
 #ifdef UNIX_FIND_STACK_BOUNDS
   struct rlimit rl;
 #endif
   
   deeper = scheme_get_deeper_address();
-  scheme_stack_grows_up = (deeper > (unsigned long)&v);
+  stack_grows_up = (deeper > (unsigned long)&v);
 
 #ifdef STACK_GROWS_UP
-  if (!scheme_stack_grows_up) {
+  if (!stack_grows_up) {
     if (scheme_console_printf)
       scheme_console_printf("Stack grows DOWN, not UP.\n");
     else
@@ -559,7 +557,7 @@ void scheme_init_stack_check()
   }
 #endif
 #ifdef STACK_GROWS_DOWN
-  if (scheme_stack_grows_up) {
+  if (stack_grows_up) {
     if (scheme_console_printf)
       scheme_console_printf("Stack grows UP, not DOWN.\n");
     else
@@ -570,7 +568,7 @@ void scheme_init_stack_check()
 
 #ifdef ASSUME_FIXED_STACK_SIZE
   scheme_stack_boundary = scheme_get_stack_base();
-  if (scheme_stack_grows_up)
+  if (stack_grows_up)
     scheme_stack_boundary += (FIXED_STACK_SIZE - STACK_SAFETY_MARGIN);
   else
     scheme_stack_boundary += (STACK_SAFETY_MARGIN - FIXED_STACK_SIZE);
@@ -618,7 +616,7 @@ void scheme_init_stack_check()
       lim = UNIX_STACK_MAXIMUM;
 # endif
 
-    if (scheme_stack_grows_up)
+    if (stack_grows_up)
       bnd += (lim - STACK_SAFETY_MARGIN);
     else
       bnd += (STACK_SAFETY_MARGIN - lim);
diff --git a/src/mzscheme/src/network.c b/src/mzscheme/src/network.c
index a6aa427d89..428d4e84a8 100644
--- a/src/mzscheme/src/network.c
+++ b/src/mzscheme/src/network.c
@@ -2714,14 +2714,12 @@ static Scheme_Object *udp_bind_or_connect(const char *name, int argc, Scheme_Obj
       }
       errid = SOCK_ERRNO();
     } else {
-      int ok;
+      int ok = 1;
 
 #ifdef USE_NULL_TO_DISCONNECT_UDP
       if (!origid) {
 	if (udp->connected)
 	  ok = !connect(udp->s, NULL, 0);
-	else
-	  ok = 1;
       } else
 #endif
 	{
diff --git a/src/mzscheme/src/schmach.h b/src/mzscheme/src/schmach.h
index 2acc5afafa..d66b24431b 100644
--- a/src/mzscheme/src/schmach.h
+++ b/src/mzscheme/src/schmach.h
@@ -25,21 +25,24 @@
 
 /* If stacks grow up then */
 
-#if !defined(STACK_GROWS_UP) && !defined(STACK_GROWS_DOWN)
-# define STACK_GROWS_UNKNOWN
+ /* STACK_GROWS_UP means that deeper stack values have higher
+     numbered addresses.
+    STACK_GROWS_DOWN means that deeper stack values have lower
+     numbered addresses. This is usually the case (Sparc and
+     Intel platforms, for example, use this). */
+
+#if STACK_DIRECTION > 0
+# define STACK_GROWS_UP
+#else
+# define STACK_GROWS_DOWN
 #endif
 
 #ifdef STACK_GROWS_UP
 # define STK_COMP(a,b) ((a) > (b))
 # define STK_DIFF(a, b) ((a) - (b))
 #else
-# ifdef STACK_GROWS_DOWN
-#  define STK_COMP(a,b) ((a) < (b))
+# define STK_COMP(a,b) ((a) < (b))
 # define STK_DIFF(a, b) ((b) - (a))
-# else
-#  define STK_COMP(a,b) (scheme_stack_grows_up == ((a) > (b)))
-#  define STK_DIFF(a,b) (scheme_stack_grows_up ? ((b) - (a)) : ((a) - (b)))
-# endif
 #endif
 
 #ifdef SHORT_ALIGN
@@ -48,8 +51,6 @@ typedef short stack_val;
 typedef long stack_val;
 #endif
 
-extern int scheme_stack_grows_up;
-
 #ifndef STACK_SAFETY_MARGIN
 # define STACK_SAFETY_MARGIN 50000
 #endif
diff --git a/src/mzscheme/src/setjmpup.c b/src/mzscheme/src/setjmpup.c
index 35d8546695..97c104b863 100644
--- a/src/mzscheme/src/setjmpup.c
+++ b/src/mzscheme/src/setjmpup.c
@@ -28,14 +28,9 @@
 #include "schgc.h"
 
 #ifdef STACK_GROWS_UP
-#define DEEPPOS(b) ((unsigned long)(b)->stack_from+(unsigned long)(b)->stack_size)
+# define DEEPPOS(b) ((unsigned long)(b)->stack_from+(unsigned long)(b)->stack_size)
 #else
-#ifdef STACK_GROWS_DOWN
-#define DEEPPOS(b) ((unsigned long)(b)->stack_from)
-#else
-#define DEEPPOS(b) ((unsigned long)(b)->stack_from+ \
-                 (scheme_stack_grows_up ? (unsigned long)(b)->stack_size : 0))
-#endif
+# define DEEPPOS(b) ((unsigned long)(b)->stack_from)
 #endif
 
 #ifdef MZ_PRECISE_GC
@@ -258,12 +253,12 @@ void scheme_copy_stack(Scheme_Jumpup_Buf *b, void *base, void *start GC_VAR_STAC
   here = &size;
 
   size = (long)here XFORM_OK_MINUS (long)start;
-  if (scheme_stack_grows_up) {
-    b->stack_from = start;
-  } else {
-    size = -size;
-    b->stack_from = here;
-  }
+#ifdef STACK_GROWS_UP
+  b->stack_from = start;
+#else
+  size = -size;
+  b->stack_from = here;
+#endif
 
   if (size < 0)
     size = 0;
@@ -361,16 +356,16 @@ static void uncopy_stack(int ok, Scheme_Jumpup_Buf *b, long *prev)
     memcpy(cto, cfrom, size);
 
     if (c->cont) {
-      if (scheme_stack_grows_up) {
-	top_delta = ((unsigned long)c->stack_from 
-		     - ((unsigned long)c->cont->buf.stack_from
-			+ c->cont->buf.stack_size));
-      } else {
-	bottom_delta = ((unsigned long)c->stack_from 
-			+ c->stack_size
-			- (unsigned long)c->cont->buf.stack_from);
-	top_delta = bottom_delta;
-      }
+#ifdef STACK_GROWS_UP
+      top_delta = ((unsigned long)c->stack_from 
+		   - ((unsigned long)c->cont->buf.stack_from
+		      + c->cont->buf.stack_size));
+#else
+      bottom_delta = ((unsigned long)c->stack_from 
+		      + c->stack_size
+		      - (unsigned long)c->cont->buf.stack_from);
+      top_delta = bottom_delta;
+#endif
       c = &c->cont->buf;
     } else
       c = NULL;
@@ -411,19 +406,19 @@ static long find_same(char *p, char *low, long max_size)
     max_size = MAX_STACK_DIFF;
   }
 
-  if (scheme_stack_grows_up) {
-    while (max_size--) {
-      if (p[cnt] != low[cnt])
-	break;
-      cnt++;
-    }
-  } else {
-    while (max_size--) {
-      if (p[max_size] != low[max_size])
-	break;
-      cnt++;
-    }
+#ifdef STACK_GROWS_UP
+  while (max_size--) {
+    if (p[cnt] != low[cnt])
+      break;
+    cnt++;
   }
+#else
+  while (max_size--) {
+    if (p[max_size] != low[max_size])
+      break;
+    cnt++;
+  }
+#endif
 
   if (cnt & (SHARED_STACK_ALIGNMENT - 1)) {
     cnt -= (cnt & (SHARED_STACK_ALIGNMENT - 1));
@@ -435,15 +430,63 @@ static long find_same(char *p, char *low, long max_size)
 #ifdef MZ_PRECISE_GC
 static void *align_var_stack(void **vs, void *s)
 {
+  void **nvs, **next;
+  long i, cnt;
+  void *a;
+  
   while (STK_COMP((unsigned long)vs, (unsigned long)s)) {
     vs = (void **)(*vs);
   }
-  return (void *)vs;
+
+  s = (void *)vs;
+
+  /* Check next few frames to see whether they refer to variables
+     before s. This can happen due to inlining, so that an older
+     frame is shallower in the stack. It shouldn't happen much,
+     though. */
+  nvs = *vs;
+  while (nvs) {
+    next = NULL;
+    cnt = ((long *)nvs)[1];
+    for (i = 0; i < cnt; i++) {
+      a = nvs[i+2];
+      if (!a) {
+	a = nvs[i+3];
+	i += 2;
+      }
+      if (STK_COMP((unsigned long)a, (unsigned long)s)) {
+	/* We need nvs to update part of copied stack! */
+	vs = nvs;
+	s = (void *)vs;
+	next = *nvs;
+	break;
+      }
+    }
+    nvs = next;
+  }
+
+  return s;
 }
 #define ALIGN_VAR_STACK(vs, s) s = align_var_stack(vs, s)
+
+static void *shift_var_stack(void *s)
+{
+#ifdef STACK_GROWS_UP
+  return s;
+#else
+  void **vs = (void **)s;
+  long cnt;
+  
+  /* Set s past end of vs: */
+  cnt = ((long *)vs)[1];
+  return (void *)(vs + cnt + 2);
+#endif
+}
+#define PAST_VAR_STACK(s) s = shift_var_stack(s);
 END_XFORM_SKIP;
 #else
 # define ALIGN_VAR_STACK(vs, s) /* empty */
+# define PAST_VAR_STACK(s) /* empty */
 #endif
 
 int scheme_setjmpup_relative(Scheme_Jumpup_Buf *b, void *base,
@@ -458,9 +501,6 @@ int scheme_setjmpup_relative(Scheme_Jumpup_Buf *b, void *base,
 
   FLUSH_REGISTER_WINDOWS;
 
-  if (STK_COMP((unsigned long)start, (unsigned long)&local))
-    start = (void *)&local;
-
   if (!(local = scheme_setjmp(b->buf))) {
     if (c) {
       /* We'd like to re-use the stack copied for a continuation
@@ -481,17 +521,19 @@ int scheme_setjmpup_relative(Scheme_Jumpup_Buf *b, void *base,
       START_XFORM_SKIP;
       same_size = find_same(get_copy(c->buf.stack_copy), c->buf.stack_from, c->buf.stack_size);
       b->cont = c;
-      if (scheme_stack_grows_up) {
-	start = (void *)((char *)c->buf.stack_from + same_size);
-      } else {
-	start = (void *)((char *)c->buf.stack_from + (c->buf.stack_size - same_size));
-      }
-      /* In 3m-mode, we need to copy on a var-stack boundary: */
+#ifdef STACK_GROWS_UP
+      start = (void *)((char *)c->buf.stack_from + same_size);
+#else
+      start = (void *)((char *)c->buf.stack_from + (c->buf.stack_size - same_size));
+#endif
+      /* In 3m-mode, we need `start' on a var-stack boundary: */
       ALIGN_VAR_STACK(__gc_var_stack__, start);
       END_XFORM_SKIP;
     } else
       b->cont = NULL;
 
+    /* In 3m-mode, we need `start' at the end of the frame */
+    PAST_VAR_STACK(start);
 
     /* b is a pointer into the middle of `base', which bad for precise
      gc, so we hide it. */
diff --git a/src/worksp/mzconfig.h b/src/worksp/mzconfig.h
index 977415b526..b32b30f50f 100644
--- a/src/worksp/mzconfig.h
+++ b/src/worksp/mzconfig.h
@@ -4,7 +4,11 @@
  * things that should be defined here.
  */
 
-/* These are not used on Windows. */
+#ifndef __MZSCHEME_CONFIGURATION_INFO__
+#define __MZSCHEME_CONFIGURATION_INFO__
+
+
+/* Undefined items are not used on Windows. */
 
 /* The size of a `char', as computed by sizeof. */
 #undef SIZEOF_CHAR
@@ -21,9 +25,14 @@
 /* The size of a `long long', as computed by sizeof. */
 #undef SIZEOF_LONG_LONG
 
+/* Direction of stack growth: 1 = up, -1 = down, 0 = unknown */
+#define STACK_DIRECTION -1
 
 /* whether nl_langinfo works */
 #undef HAVE_CODESET
 
 /* whether getaddrinfo works */
 #define HAVE_GETADDRINFO 1
+
+
+#endif