objtool: Ignore unreachable fake jumps

It is possible for alternative code to unconditionally jump out of the
alternative region. In such a case, if a fake jump is added at the end
of the alternative instructions, the fake jump will never be reached.
Since the fake jump is just a mean to make sure code validation does not
go beyond the set of alternatives, reaching it is not a requirement.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

Author: Julien Thierry

tools/objtool/check.c

@@ -2648,6 +2648,9 @@ static bool ignore_unreachable_insn(struct instruction *insn)
 	    !strcmp(insn->sec->name, ".altinstr_aux"))
 		return true;
 
+	if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->offset == FAKE_JUMP_OFFSET)
+		return true;
+
 	if (!insn->func)
 		return false;