From ffbcadfb4197213d55222bca3ecc52606cd980f4 Mon Sep 17 00:00:00 2001
From: Roberto I <roberto@inf.puc-rio.br>
Date: Fri, 5 Sep 2025 15:29:15 -0300
Subject: In C++, 'throw' must go to the correct handler.

In C, we may have several "setjmp" nested, and the "longjmp" will go
to the one given by the corresponding "jmp_buf". In C++, a "throw"
will always go to the inner "catch". So, the "catch" must check
whether it is the recipient of the "throw" and, if not, rethrow
the exception to the outer level.
---
 ldo.c | 42 +++++++++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/ldo.c b/ldo.c
index dff9488e..44937068 100644
--- a/ldo.c
+++ b/ldo.c
@@ -57,10 +57,18 @@
 ** =======================================================
 */
 
+/* chained list of long jump buffers */
+typedef struct lua_longjmp {
+  struct lua_longjmp *previous;
+  jmp_buf b;
+  volatile TStatus status;  /* error code */
+} lua_longjmp;
+
+
 /*
 ** LUAI_THROW/LUAI_TRY define how Lua does exception handling. By
 ** default, Lua handles errors with exceptions when compiling as
-** C++ code, with _longjmp/_setjmp when asked to use them, and with
+** C++ code, with _longjmp/_setjmp when available (POSIX), and with
 ** longjmp/setjmp otherwise.
 */
 #if !defined(LUAI_THROW)				/* { */
@@ -69,38 +77,38 @@
 
 /* C++ exceptions */
 #define LUAI_THROW(L,c)		throw(c)
-#define LUAI_TRY(L,c,f,ud) \
-    try { (f)(L, ud); } catch(...) { if ((c)->status == 0) (c)->status = -1; }
-#define luai_jmpbuf		int  /* dummy field */
+
+static void LUAI_TRY (lua_State *L, lua_longjmp *c, Pfunc f, void *ud) {
+  try {
+    f(L, ud);  /* call function protected */
+  }
+  catch (lua_longjmp *c1) { /* Lua error */
+    if (c1 != c)  /* not the correct level? */
+      throw;  /* rethrow to upper level */
+  }
+  catch (...) {  /* non-Lua exception */
+    c->status = -1;  /* create some error code */
+  }
+}
+
 
 #elif defined(LUA_USE_POSIX)				/* }{ */
 
-/* in POSIX, try _longjmp/_setjmp (more efficient) */
+/* in POSIX, use _longjmp/_setjmp (more efficient) */
 #define LUAI_THROW(L,c)		_longjmp((c)->b, 1)
 #define LUAI_TRY(L,c,f,ud)	if (_setjmp((c)->b) == 0) ((f)(L, ud))
-#define luai_jmpbuf		jmp_buf
 
 #else							/* }{ */
 
 /* ISO C handling with long jumps */
 #define LUAI_THROW(L,c)		longjmp((c)->b, 1)
 #define LUAI_TRY(L,c,f,ud)	if (setjmp((c)->b) == 0) ((f)(L, ud))
-#define luai_jmpbuf		jmp_buf
 
 #endif							/* } */
 
 #endif							/* } */
 
 
-
-/* chain list of long jump buffers */
-struct lua_longjmp {
-  struct lua_longjmp *previous;
-  luai_jmpbuf b;
-  volatile TStatus status;  /* error code */
-};
-
-
 void luaD_seterrorobj (lua_State *L, TStatus errcode, StkId oldtop) {
   if (errcode == LUA_ERRMEM) {  /* memory error? */
     setsvalue2s(L, oldtop, G(L)->memerrmsg); /* reuse preregistered msg. */
@@ -151,7 +159,7 @@ l_noret luaD_throwbaselevel (lua_State *L, TStatus errcode) {
 
 TStatus luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud) {
   l_uint32 oldnCcalls = L->nCcalls;
-  struct lua_longjmp lj;
+  lua_longjmp lj;
   lj.status = LUA_OK;
   lj.previous = L->errorJmp;  /* chain new error handler */
   L->errorJmp = &lj;
-- 
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