Commit b17ef2ed authored Mar 02, 2017 by Steven Rostedt (VMware)

jump_label: Add comment about initialization order for anonymous unions

Commit 3821fd35 ("jump_label: Reduce the size of struct static_key")
broke old compilers that could not handle static initialization of anonymous
unions. Boris fixed it with a patch that added brackets around the static
initializer. But this creates a dependency between those initializers and
the structure's order of its fields. Document this dependency in case new
fields are added to struct static_key in the future.

Noted-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Suggested-by: Chris Mason <clm@fb.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent cd8d860d

include/linux/jump_label.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -90,6 +90,13 @@ extern bool static_key_initialized;
		struct static_key {
		atomic_t enabled;
		/*
		* Note:
		* To make anonymous unions work with old compilers, the static
		* initialization of them requires brackets. This creates a dependency
		* on the order of the struct with the initializers. If any fields
		* are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
		* to be modified.
		*
		* bit 0 => 1 if key is initially true
		* 0 if initially false
		* bit 1 => 1 if points to struct static_key_mod