[newlib-cygwin] Cygwin: threads: use mmap area to fulfill requests for big stacks

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=aa4d9603069503207e399b6240d12b46a8df6414

commit aa4d9603069503207e399b6240d12b46a8df6414
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Tue Apr 7 14:09:45 2020 +0200

    Cygwin: threads: use mmap area to fulfill requests for big stacks
    
    Otherwise big stacks have a higher probability to collide with
    randomized PEBs and TEBs after fork.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/miscfuncs.cc | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/miscfuncs.cc b/winsup/cygwin/miscfuncs.cc
index 1ed9684f1..e1eb5e8e2 100644
--- a/winsup/cygwin/miscfuncs.cc
+++ b/winsup/cygwin/miscfuncs.cc
@@ -515,11 +515,13 @@ public:
     BOOL overflow = FALSE;
     PVOID real_stackaddr = NULL;
 
-    /* If an application requests a monster stack, we fulfill this request
-       from outside of our pool, top down. */
+    /* If an application requests a monster stack, fulfill request
+       from mmap area. */
     if (real_size > THREAD_STACK_MAX)
-      return VirtualAlloc (NULL, real_size, MEM_RESERVE | MEM_TOP_DOWN,
-			   PAGE_READWRITE);
+      {
+	PVOID addr = mmap_alloc.alloc (NULL, real_size, false);
+	return VirtualAlloc (addr, real_size, MEM_RESERVE, PAGE_READWRITE);
+      }
     /* Simple round-robin.  Keep looping until VirtualAlloc succeeded, or
        until we overflowed and hit the current address. */
     for (UINT_PTR addr = current - real_size;