From 1d75cd4d7be638babe6d4e47bf73ea05fc65d81c Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Sun, 27 Nov 2022 15:25:32 +0100
Subject: [PATCH] Avoid assertion in case of stack overflow from stitched
 trace.

Reported by Sergey Bronnikov. Fixed by Sergey Kaplun.
---
 src/lj_debug.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/lj_debug.c b/src/lj_debug.c
index 112f5358..ca893153 100644
--- a/src/lj_debug.c
+++ b/src/lj_debug.c
@@ -101,9 +101,12 @@ static BCPos debug_framepc(lua_State *L, GCfunc *fn, cTValue *nextframe)
   pos = proto_bcpos(pt, ins) - 1;
 #if LJ_HASJIT
   if (pos > pt->sizebc) {  /* Undo the effects of lj_trace_exit for JLOOP. */
-    GCtrace *T = (GCtrace *)((char *)(ins-1) - offsetof(GCtrace, startins));
-    lj_assertL(bc_isret(bc_op(ins[-1])), "return bytecode expected");
-    pos = proto_bcpos(pt, mref(T->startpc, const BCIns));
+    if (bc_isret(bc_op(ins[-1]))) {
+      GCtrace *T = (GCtrace *)((char *)(ins-1) - offsetof(GCtrace, startins));
+      pos = proto_bcpos(pt, mref(T->startpc, const BCIns));
+    } else {
+      pos = NO_BCPOS;  /* Punt in case of stack overflow for stitched trace. */
+    }
   }
 #endif
   return pos;