From 0bee44c9dc9bee64d1143aa0febd2b61819d35bd Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Sat, 21 Dec 2019 13:52:47 +0100
Subject: [PATCH] Properly fix pointer diff in string.find().

Thanks to Vyacheslav Egorov.
---
 src/lj_ffrecord.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/lj_ffrecord.c b/src/lj_ffrecord.c
index cb374beb..c673d650 100644
--- a/src/lj_ffrecord.c
+++ b/src/lj_ffrecord.c
@@ -949,8 +949,8 @@ static void LJ_FASTCALL recff_string_find(jit_State *J, RecordFFData *rd)
 		    str->len-(MSize)start, pat->len)) {
       TRef pos;
       emitir(IRTG(IR_NE, IRT_PGC), tr, trp0);
-      /* Don't use STRREF of trstr. We need a pointer diff. */
-      pos = emitir(IRTI(IR_SUB), emitir(IRTI(IR_SUB), tr, trstr), lj_ir_kint(J, sizeof(GCstr)));
+      /* Recompute offset. trsptr may not point into trstr after folding. */
+      pos = emitir(IRTI(IR_ADD), emitir(IRTI(IR_SUB), tr, trsptr), trstart);
       J->base[0] = emitir(IRTI(IR_ADD), pos, lj_ir_kint(J, 1));
       J->base[1] = emitir(IRTI(IR_ADD), pos, trplen);
       rd->nres = 2;