From 4fbce79521457be14ca4af385368495442daa11e Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Thu, 24 Oct 2024 09:09:40 +0200
Subject: [PATCH] Fix UndefinedBehaviorSanitizer error

UBSan is right to complain that `s->ptr_last == NULL` when tracing is
disabled.
---
 quickjs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/quickjs.c b/quickjs.c
index 8573578..892a05c 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -35019,7 +35019,8 @@ static JSValue JS_ReadFunctionTag(BCReaderState *s)
         goto fail;
     if (b->source_len) {
         bc_read_trace(s, "source: %d bytes\n", b->source_len);
-        s->ptr_last += b->source_len;  // omit source code hex dump
+        if (s->ptr_last)
+            s->ptr_last += b->source_len;  // omit source code hex dump
         /* b->source is a UTF-8 encoded null terminated C string */
         b->source = js_mallocz(ctx, b->source_len + 1);
         if (!b->source)