From e4a38eb0e828e9589c391171e2e1904a3b9698e7 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 19 Oct 2020 15:55:25 -0300
Subject: [PATCH] Fixed wrong trace of vararg functions

Trace of vararg functions was skipping an instruction when returning
from a call. (Bug introduced by commit 5d8ce05b3.)
---
 lvm.c         | 45 +++++++++++++++++++++++++--------------------
 testes/db.lua | 10 ++++++++++
 2 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/lvm.c b/lvm.c
index 72d3e695..aa3b22bf 100644
--- a/lvm.c
+++ b/lvm.c
@@ -1092,15 +1092,11 @@ void luaV_finishOp (lua_State *L) {
 #define ProtectNT(exp)  (savepc(L), (exp), updatetrap(ci))
 
 /*
-** Protect code that will finish the loop (returns) or can only raise
-** errors. (That is, it will not return to the interpreter main loop
-** after changing the stack or hooks.)
+** Protect code that can only raise errors. (That is, it cannnot change
+** the stack or hooks.)
 */
 #define halfProtect(exp)  (savestate(L,ci), (exp))
 
-/* idem, but without changing the stack */
-#define halfProtectNT(exp)  (savepc(L), (exp))
-
 /* 'c' is the limit of live values in the stack */
 #define checkGC(L,c)  \
 	{ luaC_condGC(L, (savepc(L), L->top = (c)), \
@@ -1132,17 +1128,20 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
 #if LUA_USE_JUMPTABLE
 #include "ljumptab.h"
 #endif
- execute:
+ startfunc:
   trap = L->hookmask;
+ returning:  /* trap already set */
   cl = clLvalue(s2v(ci->func));
   k = cl->p->k;
   pc = ci->u.l.savedpc;
   if (trap) {
-    if (cl->p->is_vararg)
-      trap = 0;  /* hooks will start after VARARGPREP instruction */
-    else if (pc == cl->p->code)  /* first instruction (not resuming)? */
-      luaD_hookcall(L, ci);
-    ci->u.l.trap = 1;  /* there may be other hooks */
+    if (pc == cl->p->code) {  /* first instruction (not resuming)? */
+      if (cl->p->is_vararg)
+        trap = 0;  /* hooks will start after VARARGPREP instruction */
+      else  /* check 'call' hook */
+        luaD_hookcall(L, ci);
+    }
+    ci->u.l.trap = 1;  /* assume trap is on, for now */
   }
   base = ci->func + 1;
   /* main loop of interpreter */
@@ -1615,10 +1614,10 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         savepc(L);  /* in case of errors */
         if ((newci = luaD_precall(L, ra, nresults)) == NULL)
           updatetrap(ci);  /* C call; nothing else to be done */
-        else {  /* Lua call: run function in this same invocation */
+        else {  /* Lua call: run function in this same C frame */
           ci = newci;
           ci->callstatus = 0;  /* call re-uses 'luaV_execute' */
-          goto execute;
+          goto startfunc;
         }
         vmbreak;
       }
@@ -1631,7 +1630,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
           L->top = ra + b;
         else  /* previous instruction set top */
           b = cast_int(L->top - ra);
-        savepc(ci);  /* some calls here can raise errors */
+        savepc(ci);  /* several calls here can raise errors */
         if (TESTARG_k(i)) {
           /* close upvalues from current call; the compiler ensures
              that there are no to-be-closed variables here, so this
@@ -1650,11 +1649,12 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
           updatestack(ci);  /* stack may have been relocated */
           ci->func -= delta;  /* restore 'func' (if vararg) */
           luaD_poscall(L, ci, cast_int(L->top - ra));  /* finish caller */
+          updatetrap(ci);  /* 'luaD_poscall' can change hooks */
           goto ret;  /* caller returns after the tail call */
         }
         ci->func -= delta;  /* restore 'func' (if vararg) */
         luaD_pretailcall(L, ci, ra, b);  /* prepare call frame */
-        goto execute;  /* execute the callee */
+        goto startfunc;  /* execute the callee */
       }
       vmcase(OP_RETURN) {
         int n = GETARG_B(i) - 1;  /* number of results */
@@ -1673,12 +1673,15 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
           ci->func -= ci->u.l.nextraargs + nparams1;
         L->top = ra + n;  /* set call for 'luaD_poscall' */
         luaD_poscall(L, ci, n);
+        updatetrap(ci);  /* 'luaD_poscall' can change hooks */
         goto ret;
       }
       vmcase(OP_RETURN0) {
         if (L->hookmask) {
           L->top = ra;
-          halfProtectNT(luaD_poscall(L, ci, 0));  /* no hurry... */
+          savepc(ci);
+          luaD_poscall(L, ci, 0);  /* no hurry... */
+          trap = 1;
         }
         else {  /* do the 'poscall' here */
           int nres = ci->nresults;
@@ -1692,7 +1695,9 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
       vmcase(OP_RETURN1) {
         if (L->hookmask) {
           L->top = ra + 1;
-          halfProtectNT(luaD_poscall(L, ci, 1));  /* no hurry... */
+          savepc(ci);
+          luaD_poscall(L, ci, 1);  /* no hurry... */
+          trap = 1;
         }
         else {  /* do the 'poscall' here */
           int nres = ci->nresults;
@@ -1706,12 +1711,12 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
               setnilvalue(s2v(L->top++));
           }
         }
-       ret:
+       ret:  /* return from a Lua function */
         if (ci->callstatus & CIST_FRESH)
           return;  /* end this frame */
         else {
           ci = ci->previous;
-          goto execute;  /* continue running caller in this frame */
+          goto returning;  /* continue running caller in this frame */
         }
       }
       vmcase(OP_FORLOOP) {
diff --git a/testes/db.lua b/testes/db.lua
index 5377f6ec..fdb0da4a 100644
--- a/testes/db.lua
+++ b/testes/db.lua
@@ -119,6 +119,16 @@ else
 end
 ]], {2,3,4,7})
 
+test([[
+local function foo()
+end
+foo()
+A = 1
+A = 2
+A = 3
+]], {2, 3, 2, 4, 5, 6})
+
+
 test([[--
 if nil then
   a=1