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Index: lib/libc/sys/mmap.2
===================================================================
--- lib/libc/sys/mmap.2
+++ lib/libc/sys/mmap.2
@@ -28,7 +28,7 @@
.\" @(#)mmap.2 8.4 (Berkeley) 5/11/95
.\" $FreeBSD$
.\"
-.Dd February 4, 2017
+.Dd June 22, 2017
.Dt MMAP 2
.Os
.Sh NAME
@@ -199,9 +199,21 @@
.Dv MAP_EXCL
is specified, the request will fail if a mapping
already exists within the range.
-.It Dv MAP_HASSEMAPHORE
-Notify the kernel that the region may contain semaphores and that special
-handling may be necessary.
+.It Dv MAP_GUARD
+Instead of a mapping, create a guard of the specified size.
+Guards allow a process to create reservations in its address space,
+which can later be replaced by actual mappings.
+.Pp
+.Fa mmap
+will not create mappings in the address range of a guard unless
+the request specifies
+.Dv MAP_FIXED .
+Guards can be destroyed with
+.Xr munmap 2 .
+Any memory access by a thread to the guarded range results
+in the delivery of a
+.Dv SIGSEGV
+signal to that thread.
.It Dv MAP_NOCORE
Region is not included in a core file.
.It Dv MAP_NOSYNC
@@ -306,6 +318,7 @@
.Dv PROT_READ
and
.Dv PROT_WRITE .
+.Pp
This option creates
a memory region that grows to at most
.Fa len
@@ -316,6 +329,10 @@
bytes.
The bottom of the stack at maximum growth is the starting
address returned by the call.
+The system uses guards to prevent the inadvertent use of
+regions into which stacks created with
+.Dv MAP_STACK
+will automatically grow, without mapping the whole stack in advance.
.El
.Pp
The
@@ -458,6 +475,16 @@
was specified, but
.Dv MAP_FIXED
was not.
+.It Bq Er EINVAL
+.Dv MAP_GUARD
+was specified, but either the
+.Fa offset
+argument was not zero, or the
+.Fa fd
+argument was not -1, or the
+.Fa prot
+argument was not
+.Dv PROT_NONE .
.It Bq Er ENODEV
.Dv MAP_ANON
has not been specified and
Index: lib/libc/sys/munmap.2
===================================================================
--- lib/libc/sys/munmap.2
+++ lib/libc/sys/munmap.2
@@ -28,7 +28,7 @@
.\" @(#)munmap.2 8.3 (Berkeley) 5/27/94
.\" $FreeBSD$
.\"
-.Dd May 27, 1994
+.Dd June 22, 2017
.Dt MUNMAP 2
.Os
.Sh NAME
@@ -44,7 +44,7 @@
The
.Fn munmap
system call
-deletes the mappings for the specified address range,
+deletes the mappings and guards for the specified address range,
and causes further references to addresses within the range
to generate invalid memory references.
.Sh RETURN VALUES

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