Index: head/share/mk/bsd.mkopt.mk
===================================================================
--- head/share/mk/bsd.mkopt.mk	(revision 279897)
+++ head/share/mk/bsd.mkopt.mk	(revision 279898)
@@ -1,60 +1,72 @@
 #
 # $FreeBSD$
 #
 # Generic mechanism to deal with WITH and WITHOUT options and turn
 # them into MK_ options.
 #
 # For each option FOO in __DEFAULT_YES_OPTIONS, MK_FOO is set to
 # "yes", unless WITHOUT_FOO is defined, in which case it is set to
 # "no".
 #
 # For each option FOO in __DEFAULT_NO_OPTIONS, MK_FOO is set to "no",
 # unless WITH_FOO is defined, in which case it is set to "yes".
 #
 # If both WITH_FOO and WITHOUT_FOO are defined, WITHOUT_FOO wins and
 # MK_FOO is set to "no" regardless of which list it was in.
 #
 # Both __DEFAULT_YES_OPTIONS and __DEFAULT_NO_OPTIONS are undef'd
 # after all this processing, allowing this file to be included
 # multiple times with different lists.
 #
+# Other parts of the build system will set BROKEN_OPTIONS to a list
+# of options that are broken on this platform. This will not be unset
+# before returning. Clients are expected to always += this variable.
+#
 # Users should generally define WITH_FOO or WITHOUT_FOO, but the build
 # system should use MK_FOO={yes,no} when it needs to override the
 # user's desires or default behavior.
 #
 
 #
 # MK_* options which default to "yes".
 #
 .for var in ${__DEFAULT_YES_OPTIONS}
 .if !defined(MK_${var})
 .if defined(WITHOUT_${var})			# WITHOUT always wins
 MK_${var}:=	no
 .else
 MK_${var}:=	yes
 .endif
 .else
 .if ${MK_${var}} != "yes" && ${MK_${var}} != "no"
 .error "Illegal value for MK_${var}: ${MK_${var}}"
 .endif
 .endif # !defined(MK_${var})
 .endfor
 .undef __DEFAULT_YES_OPTIONS
 
 #
 # MK_* options which default to "no".
 #
 .for var in ${__DEFAULT_NO_OPTIONS}
 .if !defined(MK_${var})
 .if defined(WITH_${var}) && !defined(WITHOUT_${var}) # WITHOUT always wins
 MK_${var}:=	yes
 .else
 MK_${var}:=	no
 .endif
 .else
 .if ${MK_${var}} != "yes" && ${MK_${var}} != "no"
 .error "Illegal value for MK_${var}: ${MK_${var}}"
 .endif
 .endif # !defined(MK_${var})
 .endfor
 .undef __DEFAULT_NO_OPTIONS
+
+#
+# MK_* options which are always no, usually because they are
+# unsupported/badly broken on this architecture.
+#
+.for var in ${BROKEN_OPTIONS}
+MK_${var}:=	no
+.endfor
Index: head/sys/conf/kern.opts.mk
===================================================================
--- head/sys/conf/kern.opts.mk	(revision 279897)
+++ head/sys/conf/kern.opts.mk	(revision 279898)
@@ -1,109 +1,116 @@
 # $FreeBSD$
 
 # Options set in the build system that affect the kernel somehow.
 
 #
 # Define MK_* variables (which are either "yes" or "no") for users
 # to set via WITH_*/WITHOUT_* in /etc/src.conf and override in the
 # make(1) environment.
 # These should be tested with `== "no"' or `!= "no"' in makefiles.
 # The NO_* variables should only be set by makefiles for variables
 # that haven't been converted over.
 #
 
 # Note: bsd.own.mk must be included before the rest of kern.opts.mk to make
 # building on 10.x and earlier work. This should be removed when that's no
 # longer supported since it confounds the defaults (since it uses the host's
 # notion of defaults rather than what's default in current when building
 # within sys/modules).
 .include <bsd.own.mk>
 
 # These options are used by the kernel build process (kern.mk and kmod.mk)
 # They have to be listed here so we can build modules outside of the
 # src tree.
 
 __DEFAULT_YES_OPTIONS = \
     AUTOFS \
     BHYVE \
     BLUETOOTH \
     CCD \
     CDDL \
     CRYPT \
     CUSE \
     FORMAT_EXTENSIONS \
     INET \
     INET6 \
     IPFILTER \
     ISCSI \
     KERNEL_SYMBOLS \
     NETGRAPH \
     PF \
     SOURCELESS_HOST \
     SOURCELESS_UCODE \
     USB_GADGET_EXAMPLES \
     ZFS
 
 __DEFAULT_NO_OPTIONS = \
     EISA \
     NAND \
     OFED
 
 # expanded inline from bsd.mkopt.mk to avoid share/mk dependency
 
 # Those that default to yes
 .for var in ${__DEFAULT_YES_OPTIONS}
 .if !defined(MK_${var})
 .if defined(WITHOUT_${var})			# WITHOUT always wins
 MK_${var}:=	no
 .else
 MK_${var}:=	yes
 .endif
 .else
 .if ${MK_${var}} != "yes" && ${MK_${var}} != "no"
 .error "Illegal value for MK_${var}: ${MK_${var}}"
 .endif
 .endif # !defined(MK_${var})
 .endfor
 .undef __DEFAULT_YES_OPTIONS
 
 # Those that default to no
 .for var in ${__DEFAULT_NO_OPTIONS}
 .if !defined(MK_${var})
 .if defined(WITH_${var}) && !defined(WITHOUT_${var}) # WITHOUT always wins
 MK_${var}:=	yes
 .else
 MK_${var}:=	no
 .endif
 .else
 .if ${MK_${var}} != "yes" && ${MK_${var}} != "no"
 .error "Illegal value for MK_${var}: ${MK_${var}}"
 .endif
 .endif # !defined(MK_${var})
 .endfor
 .undef __DEFAULT_NO_OPTIONS
 
 #
+# MK_* options which are always no, usually because they are
+# unsupported/badly broken on this architecture.
+#
+.for var in ${BROKEN_OPTIONS}
+MK_${var}:=	no
+.endfor
+.undef BROKEN_OPTIONS
+#end of bsd.mkopt.mk expanded inline.
+
+#
 # MK_*_SUPPORT options which default to "yes" unless their corresponding
 # MK_* variable is set to "no".
 #
 .for var in \
     INET \
     INET6
 .if defined(WITHOUT_${var}_SUPPORT) || ${MK_${var}} == "no"
 MK_${var}_SUPPORT:= no
 .else
 .if defined(KERNBUILDDIR)	# See if there's an opt_foo.h
 OPT_${var}!= cat ${KERNBUILDDIR}/opt_${var:tl}.h; echo
 .if ${OPT_${var}} == ""		# nothing -> no
 MK_${var}_SUPPORT:= no
 .else
 MK_${var}_SUPPORT:= yes
 .endif
 .else				# otherwise, yes
 MK_${var}_SUPPORT:= yes
 .endif
 .endif
 .endfor
-
-
-