From 444c8ff19a39248307a7037354d6d259cc0e5efc Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Thu, 4 Jul 2024 00:03:40 +0200
Subject: [PATCH] Clarify that lj_buf_shrink() does not keep any buffer data.

https://www.freelists.org/post/luajit/lj-buf-shrink-may-truncate-the-data-and-sbw-point-over-the-end-of-the-buffer,1
Thanks to Junlong li.
---
 src/lj_buf.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/lj_buf.c b/src/lj_buf.c
index ae2ccd82..702c5a40 100644
--- a/src/lj_buf.c
+++ b/src/lj_buf.c
@@ -92,10 +92,8 @@ void LJ_FASTCALL lj_buf_shrink(lua_State *L, SBuf *sb)
   char *b = sb->b;
   MSize osz = (MSize)(sb->e - b);
   if (osz > 2*LJ_MIN_SBUF) {
-    MSize n = (MSize)(sb->w - b);
     b = lj_mem_realloc(L, b, osz, (osz >> 1));
-    sb->b = b;
-    sb->w = b + n;
+    sb->w = sb->b = b;  /* Not supposed to keep data across shrinks. */
     sb->e = b + (osz >> 1);
   }
   lj_assertG_(G(sbufL(sb)), !sbufisext(sb), "YAGNI shrink SBufExt");