check missing or duplicate goto labels

This patch sets ->stmt of a SYM_LABEL to the corresponding label
statement.  If ->stmt was already set, it is a duplicate label.

On the other hand, if ->stmt of a goto label is not set during
evaluation, the label was never declared.

Signed-off-by: Christopher Li <sparse@chrisli.org>

3 files changed, 45 insertions, 2 deletions

diff --git a/evaluate.c b/evaluate.c
index bebe9687..0987a5e5 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -3312,6 +3312,16 @@ static void evaluate_switch_statement(struct statement *stmt)
 	} END_FOR_EACH_PTR(sym);
 }
 
+static void evaluate_goto_statement(struct statement *stmt)
+{
+	struct symbol *label = stmt->goto_label;
+
+	if (label && !label->stmt && !lookup_keyword(label->ident, NS_KEYWORD))
+		sparse_error(stmt->pos, "label '%s' was not declared", show_ident(label->ident));
+
+	evaluate_expression(stmt->goto_expression);
+}
+
 struct symbol *evaluate_statement(struct statement *stmt)
 {
 	if (!stmt)
@@ -3370,7 +3380,7 @@ struct symbol *evaluate_statement(struct statement *stmt)
 	case STMT_LABEL:
 		return evaluate_statement(stmt->label_statement);
 	case STMT_GOTO:
-		evaluate_expression(stmt->goto_expression);
+		evaluate_goto_statement(stmt);
 		return NULL;
 	case STMT_NONE:
 		break;
diff --git a/parse.c b/parse.c
index f8ade3e0..8fbba6bf 100644
--- a/parse.c
+++ b/parse.c
@@ -2276,8 +2276,12 @@ static struct token *statement(struct token *token, struct statement **tree)
 			return s->op->statement(token, stmt);
 
 		if (match_op(token->next, ':')) {
+			struct symbol *s = label_symbol(token);
 			stmt->type = STMT_LABEL;
-			stmt->label_identifier = label_symbol(token);
+			stmt->label_identifier = s;
+			if (s->stmt)
+				sparse_error(stmt->pos, "label '%s' redefined", show_ident(token->ident));
+			s->stmt = stmt;
 			token = skip_attributes(token->next->next);
 			return statement(token, &stmt->label_statement);
 		}
diff --git a/validation/goto-label.c b/validation/goto-label.c
new file mode 100644
index 00000000..1196fdef
--- /dev/null
+++ b/validation/goto-label.c
@@ -0,0 +1,29 @@
+void foo(void)
+{
+	goto a;
+a:
+a:
+	return;
+}
+
+void g(void)
+{
+	goto a;
+a:
+	return;
+}
+
+void bar(void)
+{
+	goto neverland;
+}
+
+/*
+ * check-name: goto labels
+ *
+ * check-error-start
+goto-label.c:5:1: error: label 'a' redefined
+goto-label.c:18:9: error: label 'neverland' was not declared
+ * check-error-end
+ */
+