1 files changed, 29 insertions, 41 deletions

diff --git a/winsup/cygwin/dcrt0.cc b/winsup/cygwin/dcrt0.cc
index 5865426..26b7ec3 100644
--- a/winsup/cygwin/dcrt0.cc
+++ b/winsup/cygwin/dcrt0.cc
@@ -782,6 +782,11 @@ dll_crt0_0 ()
 	 description in wow64_test_for_64bit_parent. */
       if (wincap.wow64_has_secondary_stack ())
 	wow64_needs_stack_adjustment = wow64_test_for_64bit_parent ();
+#else
+      /* Windows 10 1511 has a stack move when a 64 bit process is started from
+	 a 32 bit process, just as it was vice versa in XP/2003. */
+      if (wincap.has_3264_stack_broken ())
+	wow64_needs_stack_adjustment = !wow64_test_for_64bit_parent ();
 #endif /* !__x86_64__ */
     }
   else
@@ -1062,67 +1067,50 @@ __cygwin_exit_return:			\n\
 extern "C" void __stdcall
 _dll_crt0 ()
 {
-#ifndef __x86_64__
+#ifdef __x86_64__
+  /* Handle 64 bit process on Windows 10 rel 1511 which has been started from
+     32 bit WOW64 process.  See comment in wow64_test_for_64bit_parent for a
+     problem description.  Unfortunately the areas the stacks would have to
+     be moved to are both taken by "something else"(tm) in both, forker and
+     forkee, so we can't use the wow64_revert_to_original_stack method as in
+     the 32 bit case.  Rather, we move the main thread stack to the stack area
+     reserved for pthread stacks for this process. */
+#define CREATE_STACK(a)	create_new_main_thread_stack(a)
+#define FIX_STACK(s)	__asm__ ("\n"				\
+				 "movq %[ADDR], %%rsp \n"	\
+				 "movq  %%rsp, %%rbp  \n"	\
+				 : : [ADDR] "r" (s))
+#else
   /* Handle WOW64 process on XP/2K3 which has been started from native 64 bit
      process.  See comment in wow64_test_for_64bit_parent for a full problem
      description. */
+#define CREATE_STACK(a)	wow64_revert_to_original_stack(a)
+#define FIX_STACK(s)	__asm__ ("\n"				\
+				 "movl  %[ADDR], %%esp \n"	\
+				 "xorl  %%ebp, %%ebp   \n"	\
+				 : : [ADDR] "r" (s))
+#endif
   if (wow64_needs_stack_adjustment && !dynamically_loaded)
     {
       /* Must be static since it's referenced after the stack and frame
 	 pointer registers have been changed. */
-      static PVOID allocationbase = 0;
+      static PVOID allocationbase;
 
-      /* Check if we just move the stack.  If so, wow64_revert_to_original_stack
-	 returns a non-NULL, 16 byte aligned address.  See comments in
-	 wow64_revert_to_original_stack for the gory details. */
-      PVOID stackaddr = wow64_revert_to_original_stack (allocationbase);
+      PVOID stackaddr = CREATE_STACK (allocationbase);
       if (stackaddr)
       	{
 	  /* 2nd half of the stack move.  Set stack pointer to new address.
 	     Set frame pointer to 0. */
-	  __asm__ ("\n\
-		   movl  %[ADDR], %%esp \n\
-		   xorl  %%ebp, %%ebp   \n"
-		   : : [ADDR] "r" (stackaddr));
+	  FIX_STACK (stackaddr);
 	  /* Now we're back on the original stack.  Free up space taken by the
 	     former main thread stack and set DeallocationStack correctly. */
 	  VirtualFree (NtCurrentTeb ()->DeallocationStack, 0, MEM_RELEASE);
 	  NtCurrentTeb ()->DeallocationStack = allocationbase;
 	}
       else
-	/* Fall back to respawn if wow64_revert_to_original_stack fails. */
+	/* Fall back to respawning if creating a new stack fails. */
 	wow64_respawn_process ();
     }
-#else
-  /* Starting with Windows 10 rel 1511, the main stack of an application is
-     not reproducible if a 64 bit process has been started from a 32 bit
-     process.  Given that we have enough virtual address space on 64 bit
-     anyway, we now move the main thread stack to the stack area reserved for
-     pthread stacks.  This allows a reproducible stack space under our own
-     control and avoids collision with the OS. */
-  if (!in_forkee && !dynamically_loaded)
-    {
-      /* Must be static since it's referenced after the stack and frame
-	 pointer registers have been changed. */
-      static PVOID allocationbase;
-
-      PVOID stackaddr = create_new_main_thread_stack (allocationbase);
-      if (stackaddr)
-	{
-	  /* 2nd half of the stack move.  Set stack pointer to new address.
-	     Don't set frame pointer to 0 since x86_64 uses the stack while
-	     evaluating NtCurrentTeb (). */
-	  __asm__ ("\n\
-		   movq %[ADDR], %%rsp \n\
-		   movq  %%rsp, %%rbp   \n"
-		   : : [ADDR] "r" (stackaddr));
-	  /* Now we're back on the new stack.  Free up space taken by the
-	     former main thread stack and set DeallocationStack correctly. */
-	  VirtualFree (NtCurrentTeb ()->DeallocationStack, 0, MEM_RELEASE);
-	  NtCurrentTeb ()->DeallocationStack = allocationbase;
-	}
-    }
-#endif /* !__x86_64__ */
   _feinitialise ();
 #ifndef __x86_64__
   main_environ = user_data->envptr;