Cygwin: Allow accessing 48 bit address space in Windows 8.1 or later

64 bit Windows started out with a 44 bit address space due to a
restriction of the AMD64 CPUs at the time.  Starting with Windows
8.1, these CPUs are not supported anymore and Windows switched to
the full 48 bit address space supported by AMD64.

Cygwin didn't follow suit yet so mmaps are still restricted to
the lower 44 bit address space.  Fix that by using a system-specific
upper address for mmap allocations, 44 bit up to Windows 8, 48 bit
starting with Windows 8.1.

While at it, move the heap by another 8 Gigs to leave some space
for a potential extension of DLL address space, and restrict the
mmap lower address so the heap can grow to 32 Gigs before colliding
with mmaps.

winsup/cygwin/heap.cc

@@ -34,9 +34,9 @@ eval_start_address ()
      executable starts at 0x1:00400000L, the Cygwin DLL starts at
      0x1:80040000L, other rebased DLLs are located in the region from
      0x2:00000000L up to 0x4:00000000L, -auto-image-based DLLs are located
-     in the region from 0x4:00000000L up to 0x6:00000000L.
+     in the region from 0x4:00000000L up to 0x6:00000000L.  Leave another
-     So we let the heap start at 0x6:00000000L. */
+     8 Gigs slack space, so lets start the heap at 0x8:00000000L. */
-  uintptr_t start_address = 0x600000000L;
+  uintptr_t start_address = 0x800000000L;
 #else
   /* Windows performs heap ASLR.  This spoils the entire region below
      0x20000000 for us, because that region is used by Windows to randomize

winsup/cygwin/mmap.cc

@@ -801,8 +801,10 @@ mmap_worker (mmap_list *map_list, fhandler_base *fh, caddr_t base, size_t len,
 #ifdef __x86_64__
 
 /* The memory region used for memory maps */
-#define MMAP_STORAGE_LOW	0x00800000000L	/* Leave 8 Gigs for heap. */
+#define MMAP_STORAGE_LOW	0x001000000000L	/* Leave 32 Gigs for heap. */
-#define MMAP_STORAGE_HIGH	0x70000000000L	/* Leave enough room for OS. */
+/* Up to Win 8 only supporting 44 bit address space, starting with Win 8.1
+   48 bit address space. */
+#define MMAP_STORAGE_HIGH	wincap.mmap_storage_high ()
 
 /* FIXME?  Unfortunately the OS doesn't support a top down allocation with
 	   a ceiling value.  The ZeroBits mechanism only works for

winsup/cygwin/wincap.cc

@@ -20,6 +20,7 @@ details. */
 
 wincaps wincap_vista __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:1,
+  mmap_storage_high:0x070000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:true,
@@ -46,6 +47,7 @@ wincaps wincap_vista __attribute__((section (".cygwin_dll_common"), shared)) = {
 
 wincaps wincap_7 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:1,
+  mmap_storage_high:0x070000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -72,6 +74,7 @@ wincaps wincap_7 __attribute__((section (".cygwin_dll_common"), shared)) = {
 
 wincaps wincap_8 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x070000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -98,6 +101,7 @@ wincaps wincap_8 __attribute__((section (".cygwin_dll_common"), shared)) = {
 
 wincaps wincap_8_1 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -124,6 +128,7 @@ wincaps wincap_8_1 __attribute__((section (".cygwin_dll_common"), shared)) = {
 
 wincaps  wincap_10_1507 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -150,6 +155,7 @@ wincaps  wincap_10_1507 __attribute__((section (".cygwin_dll_common"), shared))
 
 wincaps wincap_10_1703 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -176,6 +182,7 @@ wincaps wincap_10_1703 __attribute__((section (".cygwin_dll_common"), shared)) =
 
 wincaps wincap_10_1709 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -202,6 +209,7 @@ wincaps wincap_10_1709 __attribute__((section (".cygwin_dll_common"), shared)) =
 
 wincaps wincap_10_1803 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,
@@ -228,6 +236,7 @@ wincaps wincap_10_1803 __attribute__((section (".cygwin_dll_common"), shared)) =
 
 wincaps wincap_10_1809 __attribute__((section (".cygwin_dll_common"), shared)) = {
   def_guard_pages:2,
+  mmap_storage_high:0x700000000000LL,
   {
     is_server:false,
     needs_count_in_si_lpres2:false,

winsup/cygwin/wincap.h

@@ -12,6 +12,7 @@ details. */
 struct wincaps
 {
   DWORD def_guard_pages;
+  int64_t mmap_storage_high;
   /* The bitfields must be 8 byte aligned on x86_64, otherwise the bitfield
      ops generated by gcc are off by 4 bytes. */
   struct  __attribute__ ((aligned (8))) {
@@ -71,6 +72,9 @@ public:
   {
     return ((wincaps *) this->caps)->def_guard_pages * page_size ();
   }
+#ifdef __x86_64__
+  intptr_t IMPLEMENT (mmap_storage_high)
+#endif
   bool  IMPLEMENT (is_server)
   bool	IMPLEMENT (needs_count_in_si_lpres2)
   bool	IMPLEMENT (needs_query_information)