Add macro DECLARE_MODULE_TIED to denote a module as requiring the

kernel of exactly the same __FreeBSD_version as the headers module was
compiled against.

Mark our in-tree ABI emulators with DECLARE_MODULE_TIED. The modules
use kernel interfaces that the Release Engineering Team feel are not
stable enough to guarantee they will not change during the life cycle
of a STABLE branch. In particular, the layout of struct sysentvec is
declared to be not part of the STABLE KBI.

Discussed with:	bz, rwatson
Approved by:	re (bz, kensmith)
MFC after:	2 weeks

2 files changed, 17 insertions, 3 deletions

diff --git a/sys/sys/exec.h b/sys/sys/exec.h
index 8c95c36..140ab2e 100644
--- a/sys/sys/exec.h
+++ b/sys/sys/exec.h
@@ -115,7 +115,8 @@ int exec_unregister(const struct execsw *);
 		__CONCAT(name,_modevent), \
 		(void *)& execsw_arg \
 	}; \
-	DECLARE_MODULE(name, __CONCAT(name,_mod), SI_SUB_EXEC, SI_ORDER_ANY)
+	DECLARE_MODULE_TIED(name, __CONCAT(name,_mod), SI_SUB_EXEC, \
+	    SI_ORDER_ANY)
 #endif
 
 #endif
diff --git a/sys/sys/module.h b/sys/sys/module.h
index 2abad63..782770a 100644
--- a/sys/sys/module.h
+++ b/sys/sys/module.h
@@ -125,13 +125,26 @@ struct mod_metadata {
  */
 #define	MODULE_KERNEL_MAXVER	(roundup(__FreeBSD_version, 100000) - 1)
 
-#define	DECLARE_MODULE(name, data, sub, order)				\
+#define	DECLARE_MODULE_WITH_MAXVER(name, data, sub, order, maxver)	\
 	MODULE_DEPEND(name, kernel, __FreeBSD_version,			\
-	    __FreeBSD_version, MODULE_KERNEL_MAXVER);			\
+	    __FreeBSD_version, maxver);			\
 	MODULE_METADATA(_md_##name, MDT_MODULE, &data, #name);		\
 	SYSINIT(name##module, sub, order, module_register_init, &data);	\
 	struct __hack
 
+#define	DECLARE_MODULE(name, data, sub, order)				\
+	DECLARE_MODULE_WITH_MAXVER(name, data, sub, order, MODULE_KERNEL_MAXVER)
+
+/*
+ * The module declared with DECLARE_MODULE_TIED can only be loaded
+ * into the kernel with exactly the same __FreeBSD_version.
+ *
+ * Use it for modules that use kernel interfaces that are not stable
+ * even on STABLE/X branches.
+ */
+#define	DECLARE_MODULE_TIED(name, data, sub, order)				\
+	DECLARE_MODULE_WITH_MAXVER(name, data, sub, order, __FreeBSD_version)
+
 #define	MODULE_VERSION(module, version)					\
 	static struct mod_version _##module##_version = {		\
 		version							\