--- gc-7.2/include/gc.h	2014-06-01 19:00:48.000000000 +0200
+++ gc-7.2/include/gc.h	2015-05-27 12:55:42.248984200 +0200
@@ -1386,7 +1386,14 @@
 /* THREAD_LOCAL_ALLOC defined and the initial allocation call is not    */
 /* to GC_malloc() or GC_malloc_atomic().                                */
 
-#ifdef __CYGWIN32__
+#ifdef __CYGWIN__
+#ifdef __x86_64__
+  extern int __data_start__[], __data_end__[], __bss_start__[], __bss_end__[];
+#define GC_DATASTART (__data_start__ < __bss_start__ ?\
+                      (void *)__data_start__ : (void *)__bss_start__)
+#define GC_DATAEND (__data_end__ < __bss_end__ ?\
+                      (void *)__data_end__ : (void *)__bss_end__)
+#else
   /* Similarly gnu-win32 DLLs need explicit initialization from the     */
   /* main program, as does AIX.                                         */
   extern int _data_start__[], _data_end__[], _bss_start__[], _bss_end__[];
@@ -1394,6 +1401,7 @@
                        (void *)_data_start__ : (void *)_bss_start__)
 # define GC_DATAEND (_data_end__ > _bss_end__ ? \
                      (void *)_data_end__ : (void *)_bss_end__)
+#endif
 # define GC_INIT_CONF_ROOTS GC_add_roots(GC_DATASTART, GC_DATAEND); \
                                  GC_gcollect() /* For blacklisting. */
         /* Required at least if GC is in a DLL.  And doesn't hurt. */
--- gc-7.2/include/private/gcconfig.h	2014-06-01 19:00:48.000000000 +0200
+++ gc-7.2/include/private/gcconfig.h	2015-05-27 12:46:01.864338700 +0200
@@ -441,10 +441,20 @@
 #   endif
 #   define mach_type_known
 # endif
-# if defined(__CYGWIN32__) || defined(__CYGWIN__)
+# if defined(__CYGWIN32__)
 #   define I386
 #   define CYGWIN32
 #   define mach_type_known
+#if defined(__CYGWIN__)
+#  if defined(__LP64__)
+#    define X86_64
+#    define mach_type_known
+#  else
+#    define I386
+#  endif
+#  define CYGWIN32
+#  define mach_type_known
+#endif
 # endif
 # if defined(__MINGW32__) && !defined(mach_type_known)
 #   define I386
@@ -511,6 +521,16 @@
 #    define mach_type_known
 # endif
 
+#if defined(__CYGWIN__)
+#  if defined(__LP64__)
+#    define X86_64
+#    define mach_type_known
+#  else
+#    define I386
+#  endif
+#  define CYGWIN32
+#  define mach_type_known
+#endif
 /* Feel free to add more clauses here */
 
 /* Or manually define the machine type here.  A machine type is         */
@@ -2279,6 +2299,20 @@
 #       define GWW_VDB
 #       define DATAEND  /* not needed */
 #   endif
+
+#   ifdef CYGWIN32
+#       define OS_TYPE "CYGWIN32"
+#       define DATASTART ((ptr_t)GC_DATASTART)  /* From gc.h */
+#       define DATAEND   ((ptr_t)GC_DATAEND)
+#       define ALIGNMENT 8
+#       undef STACK_GRAN
+#       define STACK_GRAN 0x10000
+#       ifdef USE_MMAP
+#         define NEED_FIND_LIMIT
+#         define USE_MMAP_ANON
+#       endif
+#   endif
+
 # endif /* X86_64 */
 
 # ifdef HEXAGON
--- gc-7.2/os_dep.c	2015-05-27 12:25:29.097698800 +0200
+++ gc-7.2/os_dep.c	2015-05-27 12:48:23.714600800 +0200
@@ -764,10 +764,16 @@
     /* gcc version of boehm-gc).                                        */
     GC_API int GC_CALL GC_get_stack_base(struct GC_stack_base *sb)
     {
+# ifdef __x86_64__
+      PNT_TIB pTib = NtCurrentTeb();
+      void * _tlsbase = pTib->StackBase;
+      /*void * _tlsbase = NtCurrentTeb()->pTib.StackBase;*/
+      /*extern void * _tlsbase __asm__ ("%gs:8");*/
+# else
       void * _tlsbase;
-
       __asm__ ("movl %%fs:4, %0"
                : "=r" (_tlsbase));
+# endif
       sb -> mem_base = _tlsbase;
       return GC_SUCCESS;
     }