generic: fix crash when nothing match

The code for the generic selection doesn't take in account
the fact that the default entry could be absent.

Catch the case where nothing matches and issue an error.

Fixes: c100a7ab2504f9e6fe6b6d3f9a010a8ea5ed30a3
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>

2 files changed, 29 insertions, 2 deletions

diff --git a/evaluate.c b/evaluate.c
index bc69a1fa..95aef4dc 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -3299,11 +3299,15 @@ static struct symbol *evaluate_generic_selection(struct expression *expr)
 			continue;
 
 		res = map->expr;
-		goto end;
+		goto found;
 	}
 	res = expr->def;
+	if (!res) {
+		sparse_error(expr->pos, "no generic selection for '%s'", show_typename(ctrl));
+		return NULL;
+	}
 
-end:
+found:
 	*expr = *res;
 	return evaluate_expression(expr);
 }
diff --git a/validation/generic-bad0.c b/validation/generic-bad0.c
new file mode 100644
index 00000000..acc3d5e7
--- /dev/null
+++ b/validation/generic-bad0.c
@@ -0,0 +1,23 @@
+struct s;
+
+void foo(int n)
+{
+	_Generic(n, default: 1, default: 2);
+	_Generic(n, int[n]:0, default:1);
+	_Generic(n, struct s:0, default:1);
+	_Generic(n, void:0, default:1);
+	_Generic(n, void (void):0, default:1);
+	_Generic(&n, int:5, signed int:7, default:23);
+	_Generic(n, void *:5);
+}
+
+/*
+ * check-name: generic-bad0
+ *
+ * check-error-start
+generic-bad0.c:5:33: warning: multiple default in generic expression
+generic-bad0.c:5:30: note: previous was here
+generic-bad0.c:6:25: warning: Variable length array is used.
+generic-bad0.c:11:17: error: no generic selection for 'int [addressable] n'
+ * check-error-end
+ */