objtool: Provide stats for jump_labels

Add objtool --stats to count the jump_label sites it encounters.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210506194158.153101906@infradead.org

tools/objtool/check.c

@@ -1225,8 +1225,15 @@ static int handle_jump_alt(struct objtool_file *file,
 			   struct instruction *orig_insn,
 			   struct instruction **new_insn)
 {
-	if (orig_insn->type == INSN_NOP)
+	if (orig_insn->type == INSN_NOP) {
+do_nop:
+		if (orig_insn->len == 2)
+			file->jl_nop_short++;
+		else
+			file->jl_nop_long++;
+
 		return 0;
+	}
 
 	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 		WARN_FUNC("unsupported instruction at jump label",
@@ -1245,9 +1252,14 @@ static int handle_jump_alt(struct objtool_file *file,
 			       orig_insn->offset, orig_insn->len,
 			       arch_nop_insn(orig_insn->len));
 		orig_insn->type = INSN_NOP;
-		return 0;
+		goto do_nop;
 	}
 
+	if (orig_insn->len == 2)
+		file->jl_short++;
+	else
+		file->jl_long++;
+
 	*new_insn = list_next_entry(orig_insn, list);
 	return 0;
 }
@@ -1328,6 +1340,12 @@ static int add_special_section_alts(struct objtool_file *file)
 		free(special_alt);
 	}
 
+	if (stats) {
+		printf("jl\\\tNOP\tJMP\n");
+		printf("short:\t%ld\t%ld\n", file->jl_nop_short, file->jl_short);
+		printf("long:\t%ld\t%ld\n", file->jl_nop_long, file->jl_long);
+	}
+
 out:
 	return ret;
 }

tools/objtool/include/objtool/objtool.h

@@ -22,6 +22,9 @@ struct objtool_file {
 	struct list_head static_call_list;
 	struct list_head mcount_loc_list;
 	bool ignore_unreachables, c_file, hints, rodata;
+
+	unsigned long jl_short, jl_long;
+	unsigned long jl_nop_short, jl_nop_long;
 };
 
 struct objtool_file *objtool_open_read(const char *_objname);