man5/bsd.port.mk: document USE_NOBTCFI

feedback from and ok bentley@ and tb@ thanks!

diff --git a/share/man/man5/bsd.port.mk.5 b/share/man/man5/bsd.port.mk.5
index 00ec6c3..11d87d7 100644 (file)
--- a/share/man/man5/bsd.port.mk.5
+++ b/share/man/man5/bsd.port.mk.5
@@ -1,4 +1,4 @@
-.\" $OpenBSD: bsd.port.mk.5,v 1.621 2023/09/07 23:32:56 espie Exp $
+.\" $OpenBSD: bsd.port.mk.5,v 1.622 2023/09/08 21:57:09 lraab Exp $
 .\"
 .\" Copyright (c) 2000-2008 Marc Espie
 .\"
@@ -24,7 +24,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: September 7 2023 $
+.Dd $Mdocdate: September 8 2023 $
 .Dt BSD.PORT.MK 5
 .Os
 .Sh NAME
@@ -3613,6 +3613,22 @@ and not intended to be a user setting.
 See
 .Ev WRKOBJDIR_MFS
 for configuration.
+.It Ev USE_NOBTCFI
+If set to
+.Sq Yes ,
+writes a wrapper script to
+.Pa ${WRKDIR}/bin/ld
+in
+.Cm patch
+to request that the linker adds an
+.Dv PT_OPENBSD_NOBTCFI
+ELF section.
+Use when a port does not work with the default strict enforcement of
+indirect branch targets.
+.Pp
+Applies to all architectures; set
+.Ev USE_NOBTCFI-${MACHINE_ARCH}
+to apply to only a specific architecture.
 .It Ev USE_NOEXECONLY
 If set to
 .Sq Yes ,