sh: panic on machvec section misalignment.

Now that __initmv references the machvec section unconditionally
there have been cases where folks have been mistakenly flagging
non-machvec structures with the machvec section attribute (presumably
to shut up modpost). This leads to obscure breakage in earlyprintk
amongst other places and is rather non-obvious.

Add a simple sanity check to try and catch __initmv misuse and
panic early.
Reported-by: NMarkus Brunner <super.firetwister@gmail.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/kernel/machvec.c

@@ -90,6 +90,13 @@ void __init sh_mv_setup(void)
 		machvec_size = ((unsigned long)&__machvec_end -
 				(unsigned long)&__machvec_start);
 
+		/*
+		 * Sanity check for machvec section alignment. Ensure
+		 * __initmv hasn't been misused.
+		 */
+		if (machvec_size % sizeof(struct sh_machine_vector))
+			panic("machvec misaligned, invalid __initmv use?");
+
 		/*
 		 * If the machvec hasn't been preselected, use the first
 		 * vector (usually the only one) from .machvec.init.