From 59a1adf194efe43741c2bb2005d93d8320a19d14 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Tue, 1 Jul 2025 10:57:02 -0300
Subject: LUAI_MAXSTACK defined privately

LUAI_MAXSTACK is limited to INT_MAX/2, so can use INT_MAX/2 to define
pseudo-indices (LUA_REGISTRYINDEX) in 'lua.h'. A change in the maximum
stack size does not need to change the Lua-C ABI.
---
 ldo.c     | 14 ++++++++++++++
 ltests.h  |  1 -
 lua.h     |  6 +++---
 luaconf.h | 14 --------------
 4 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/ldo.c b/ldo.c
index 776519dc..f232b588 100644
--- a/ldo.c
+++ b/ldo.c
@@ -174,6 +174,20 @@ TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud) {
 #define STACKERRSPACE	200
 
 
+/*
+** LUAI_MAXSTACK limits the size of the Lua stack.
+** It must fit into INT_MAX/2.
+*/
+
+#if !defined(LUAI_MAXSTACK)
+#if 1000000 < (INT_MAX / 2)
+#define LUAI_MAXSTACK           1000000
+#else
+#define LUAI_MAXSTACK           (INT_MAX / 2u)
+#endif
+#endif
+
+
 /* maximum stack size that respects size_t */
 #define MAXSTACK_BYSIZET  ((MAX_SIZET / sizeof(StackValue)) - STACKERRSPACE)
 
diff --git a/ltests.h b/ltests.h
index 43f08162..d34e9d42 100644
--- a/ltests.h
+++ b/ltests.h
@@ -155,7 +155,6 @@ LUA_API void *debug_realloc (void *ud, void *block,
 ** Reduce maximum stack size to make stack-overflow tests run faster.
 ** (But value is still large enough to overflow smaller integers.)
 */
-#undef LUAI_MAXSTACK
 #define LUAI_MAXSTACK   68000
 
 
diff --git a/lua.h b/lua.h
index 95e0db32..131a8fcb 100644
--- a/lua.h
+++ b/lua.h
@@ -37,10 +37,10 @@
 
 /*
 ** Pseudo-indices
-** (-LUAI_MAXSTACK is the minimum valid index; we keep some free empty
-** space after that to help overflow detection)
+** (The stack size is limited to INT_MAX/2; we keep some free empty
+** space after that to help overflow detection.)
 */
-#define LUA_REGISTRYINDEX	(-LUAI_MAXSTACK - 1000)
+#define LUA_REGISTRYINDEX	(-(INT_MAX/2 + 1000))
 #define lua_upvalueindex(i)	(LUA_REGISTRYINDEX - (i))
 
 
diff --git a/luaconf.h b/luaconf.h
index 51e77547..bc5fbe9f 100644
--- a/luaconf.h
+++ b/luaconf.h
@@ -763,20 +763,6 @@
 ** =====================================================================
 */
 
-/*
-@@ LUAI_MAXSTACK limits the size of the Lua stack.
-** CHANGE it if you need a different limit. This limit is arbitrary;
-** its only purpose is to stop Lua from consuming unlimited stack
-** space and to reserve some numbers for pseudo-indices.
-** (It must fit into max(int)/2.)
-*/
-#if 1000000 < (INT_MAX / 2)
-#define LUAI_MAXSTACK		1000000
-#else
-#define LUAI_MAXSTACK		(INT_MAX / 2u)
-#endif
-
-
 /*
 @@ LUA_EXTRASPACE defines the size of a raw memory area associated with
 ** a Lua state with very fast access.
-- 
cgit v1.2.3-55-g6feb