objtool: Remove check preventing branches within alternative

While jumping from outside an alternative region to the middle of an
alternative region is very likely wrong, jumping from an alternative
region into the same region is valid. It is a common pattern on arm64.

The first pattern is unlikely to happen in practice and checking only
for this adds a lot of complexity.

Just remove the current check.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20200327152847.15294-6-jthierry@redhat.com

tools/objtool/check.c

@@ -2162,12 +2162,6 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 	sec = insn->sec;
 
-	if (insn->alt_group && list_empty(&insn->alts)) {
-		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
-			  sec, insn->offset);
-		return 1;
-	}
-
 	while (1) {
 		next_insn = next_insn_same_sec(file, insn);