From 11cd42379bd4959e29e5eb47f405f21b5fc75039 Mon Sep 17 00:00:00 2001
From: Mark <markjordanthom@gmail.com>
Date: Thu, 28 Sep 2023 15:25:57 -0600
Subject: [PATCH] do not deref AttrVar binding in redo_attr_var_binding (#2059)

---
 src/machine/system_calls.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/machine/system_calls.rs b/src/machine/system_calls.rs
index 897dab67..daa119fc 100644
--- a/src/machine/system_calls.rs
+++ b/src/machine/system_calls.rs
@@ -5659,7 +5659,9 @@ impl Machine {
     }
     #[inline(always)]
     pub(crate) fn redo_attr_var_binding(&mut self) {
-        let var = self.deref_register(1);
+        // registers[1] MUST NOT be dereferenced here. the original
+        // AttrVar binding site must be preserved.
+        let var = self.machine_st.registers[1];
         let value = self.deref_register(2);
 
         debug_assert_eq!(HeapCellValueTag::AttrVar, var.get_tag());
-- 
2.54.0