From e381622a9af715672c6a88cde6eece114ba50939 Mon Sep 17 00:00:00 2001
From: Jonathan Marler <johnnymarler@gmail.com>
Date: Sat, 11 Sep 2021 19:49:16 -0600
Subject: [PATCH] add NULL check in gc.c to avoid UB

After the UB was fixed in value.c, I tried running the build again and encoutered another instance of UB in gc.c.  With this fixed I can now build janet with ubsan enabled, meaning there's no more UB encountered in janet_boot during the build.
---
 src/core/gc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/core/gc.c b/src/core/gc.c
index b1efbe00..1a320abd 100644
--- a/src/core/gc.c
+++ b/src/core/gc.c
@@ -123,6 +123,8 @@ static void janet_mark_abstract(void *adata) {
 
 /* Mark a bunch of items in memory */
 static void janet_mark_many(const Janet *values, int32_t n) {
+    if (values == NULL)
+        return;
     const Janet *end = values + n;
     while (values < end) {
         janet_mark(*values);