[newlib-cygwin] Implement address space guards.

[newlib-cygwin] Implement address space guards.

[Sebastian Huber]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=eb82d7086c08a92d15392a181673429c6db24a09

commit eb82d7086c08a92d15392a181673429c6db24a09
Author: kib <kib@FreeBSD.org>
Date:   Sat Jun 24 17:01:11 2017 +0000

    Implement address space guards.
    
    Guard, requested by the MAP_GUARD mmap(2) flag, prevents the reuse of
    the allocated address space, but does not allow instantiation of the
    pages in the range.  It is useful for more explicit support for usual
    two-stage reserve then commit allocators, since it prevents accidental
    instantiation of the mapping, e.g. by mprotect(2).
    
    Use guards to reimplement stack grow code.  Explicitely track stack
    grow area with the guard, including the stack guard page.  On stack
    grow, trivial shift of the guard map entry and stack map entry limits
    makes the stack expansion.  Move the code to detect stack grow and
    call vm_map_growstack(), from vm_fault() into vm_map_lookup().
    
    As result, it is impossible to get random mapping to occur in the
    stack grow area, or to overlap the stack guard page.
    
    Enable stack guard page by default.
    
    Reviewed by:	alc, markj
    Man page update reviewed by:	alc, bjk, emaste, markj, pho
    Tested by:	pho, Qualys
    Sponsored by:	The FreeBSD Foundation
    MFC after:	1 week
    Differential revision:	https://reviews.freebsd.org/D11306 (man pages)

Diff:
---
 newlib/libc/sys/rtems/include/sys/mman.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/newlib/libc/sys/rtems/include/sys/mman.h b/newlib/libc/sys/rtems/include/sys/mman.h
index 8aeed87..c099e22 100644
--- a/newlib/libc/sys/rtems/include/sys/mman.h
+++ b/newlib/libc/sys/rtems/include/sys/mman.h
@@ -90,6 +90,7 @@
 /*
  * Extended flags
  */
+#define	MAP_GUARD	 0x00002000 /* reserve but don't map address range */
 #define	MAP_EXCL	 0x00004000 /* for MAP_FIXED, fail if address is used */
 #define	MAP_NOCORE	 0x00020000 /* dont include these pages in a coredump */
 #define	MAP_PREFAULT_READ 0x00040000 /* prefault mapping for reading */