Always allocate main thread stack from pthread stack area on x86_64.

* dcrt0.cc: Semi-revert commit 12743c2d5d.
        (dll_crt0_0): Drop setting wow64_needs_stack_adjustment on 64 bit.
        (_dll_crt0): Split out 64 bit code again and always create new main
        thread stack, unless forked off from the non main thread in the parent.
        Call create_new_main_thread_stack with parent stack commitsize if
        started from the parent's main thread.
        Only call child_info_fork::alloc_stack for the latter case on 64 bit.
        Slightly rearrange moving rsp and rbp to new stack and document how.
        Revert 32 bit wow64 handling to its former self.
        * miscfunc.cc (create_new_main_thread_stack): Take a commitsize
        parameter and use it if it's not 0.  Don't set _main_tls here, it's
        done in the caller _dll_crt0 anyway.  Return stackbase - 16 bytes,
        rather than stacklimit (which was very wrong anyway).
        * miscfuncs.h (create_new_main_thread_stack): Accommodate declaration
        to aforementioned change.
        * wincap.h (wincaps::has_3264_stack_broken): Remove element.
        * wincap.cc: Ditto, throughout.
        * wow64.cc: Semi-revert to pre-12743c2d5d2721f3a80b4d7671a349be03c1f520
        but keep architecture-agnostic type changes intact.  Fix formatting.
        * wow64.h: Revert to pre-12743c2d5d2721f3a80b4d7671a349be03c1f520.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/wow64.cc

@@ -8,6 +8,10 @@ This software is a copyrighted work licensed under the terms of the
 Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
+#ifndef __x86_64__
+/* WOW64 only plays a role in the 32 bit version.  Don't use any of this
+   in the 64 bit version. */
+
 #include "winsup.h"
 #include "cygtls.h"
 #include "ntdll.h"
@@ -37,15 +41,8 @@ wow64_eval_expected_main_stack (PVOID &allocbase, PVOID &stackbase)
      stack address on Vista/2008 64 bit is 0x80000 and on W7/2K8R2 64 bit
      it is 0x90000.  However, this is no problem because the system sticks
      to that address for all WOW64 processes, not only for the first one
-     started from a 64 bit parent.
-
-     On 64 bit W10 1511 the stack starts at 0x400000 by default.  See comment
-     in wow64_test_for_64bit_parent. */
-#ifdef __x86_64__
-  allocbase = (PVOID) 0x400000;
-#else
+     started from a 64 bit parent. */
   allocbase = (PVOID) 0x30000;
-#endif
   /* Stack size.  The OS always rounds the size up to allocation granularity
      and it never allocates less than 256K. */
   size = roundup2 (ntheader->OptionalHeader.SizeOfStackReserve,
@@ -79,14 +76,6 @@ wow64_test_for_64bit_parent ()
      process here.  If so, we note this fact in wow64_needs_stack_adjustment
      so we can workaround the stack problem in _dll_crt0.  See there for how
      we go along. */
-
-  /* Amazing but true: Starting with Windows 10 1511 this problem has been
-     reintroduced, just in the opposite direction: If a 64 bit process is
-     created from a 32 bit WOW64 process, the main thread stack in the 64
-     bit child gets moved to another location than the default.  In the
-     forked child, the stack is back where it usually is when started from
-     another 64 bit process.  Therefore we have to be able to recognize
-     this scenarion now on 64 bit as well.  We I don't believe it... */
   NTSTATUS ret;
   PROCESS_BASIC_INFORMATION pbi;
   HANDLE parent;
@@ -118,8 +107,6 @@ wow64_test_for_64bit_parent ()
   return !wow64;
 }
 
-#ifndef __x86_64__
-
 PVOID
 wow64_revert_to_original_stack (PVOID &allocationbase)
 {
@@ -184,14 +171,12 @@ wow64_revert_to_original_stack (PVOID &allocationbase)
      accordingly, and return the new, 16 byte aligned address for the
      stack pointer.  The second half of the stack move is done by the
      caller _dll_crt0. */
-  NtCurrentTeb()->Tib.StackBase = (char *) newbase;
-  NtCurrentTeb()->Tib.StackLimit = (char *) newtop;
+  NtCurrentTeb ()->Tib.StackBase = (char *) newbase;
+  NtCurrentTeb ()->Tib.StackLimit = (char *) newtop;
   _main_tls = &_my_tls;
-  return PTR_ADD (NtCurrentTeb()->Tib.StackBase, -16);
+  return PTR_ADD (NtCurrentTeb ()->Tib.StackBase, -16);
 }
 
-#endif /* !__x86_64__ */
-
 /* Respawn WOW64 process. This is only called if we can't reuse the original
    stack.  See comment in wow64_revert_to_original_stack for details.  See
    _dll_crt0 for the call of this function.
@@ -226,3 +211,5 @@ wow64_respawn_process ()
   TerminateProcess (GetCurrentProcess (), ret);
   ExitProcess (ret);
 }
+
+#endif /* !__x86_64__ */