--- a/src/lgc.c
+++ b/src/lgc.c
@@ -202,7 +205,8 @@ void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
   }
   else {  /* sweep phase */
     lua_assert(issweepphase(g));
-    makewhite(g, o);  /* mark main obj. as white to avoid other barriers */
+    if (g->gckind == KGC_INC)  /* incremental mode? */
+      makewhite(g, o);  /* mark 'o' as white to avoid other barriers */
   }
 }

@@ -340,9 +349,11 @@ static int remarkupvals (global_State *g) {
       p = &thread->twups;  /* keep marked thread with upvalues in the list */
     else {  /* thread is not marked or without upvalues */
       UpVal *uv;
+      lua_assert(!isold(thread) || thread->openupval == NULL);
       *p = thread->twups;  /* remove thread from the list */
       thread->twups = thread;  /* mark that it is out of list */
       for (uv = thread->openupval; uv != NULL; uv = uv->u.open.next) {
+        lua_assert(getage(uv) <= getage(thread));
         work++;
         if (!iswhite(uv))  /* upvalue already visited? */
           markvalue(g, uv->v);  /* mark its value */
@@ -856,6 +856,8 @@ static void GCTM (lua_State *L) {
     if (unlikely(status != LUA_OK)) {  /* error while running __gc? */
       luaE_warnerror(L, "__gc metamethod");
       L->top--;  /* pops error object */
+      if (isLua(L->ci))
+        L->oldpc = L->ci->u.l.savedpc;  /* update 'oldpc' */
     }
   }
 }
@@ -1140,7 +1140,7 @@ static void finishgencycle (lua_State *L, global_State *g) {
 static void youngcollection (lua_State *L, global_State *g) {
   GCObject **psurvival;  /* to point to first non-dead survival object */
   lua_assert(g->gcstate == GCSpropagate);
-  markold(g, g->survival, g->reallyold);
+  markold(g, g->allgc, g->reallyold);
   markold(g, g->finobj, g->finobjrold);
   atomic(L);

@@ -1143,6 +1157,7 @@ static void youngcollection (lua_State *L, global_State *g) {
   atomic(L);
 
   /* sweep nursery and get a pointer to its last live element */
+  g->gcstate = GCSswpallgc;
   psurvival = sweepgen(L, g, &g->allgc, g->survival);
   /* sweep 'survival' and 'old' */
   sweepgen(L, g, psurvival, g->reallyold);
@@ -1166,6 +1181,7 @@ static void youngcollection (lua_State *L, global_State *g) {
 
 static void atomic2gen (lua_State *L, global_State *g) {
   /* sweep all elements making them old */
+  g->gcstate = GCSswpallgc;
   sweep2old(L, &g->allgc);
   /* everything alive now is old */
   g->reallyold = g->old = g->survival = g->allgc;
--- a/src/ldo.c
+++ b/src/ldo.c
@@ -466,13 +466,13 @@ void luaD_call (lua_State *L, StkId func, int nresults) {
       f = fvalue(s2v(func));
      Cfunc: {
       int n;  /* number of returns */
-      CallInfo *ci = next_ci(L);
+      CallInfo *ci;
       checkstackp(L, LUA_MINSTACK, func);  /* ensure minimum stack size */
+      L->ci = ci = next_ci(L);
       ci->nresults = nresults;
       ci->callstatus = CIST_C;
       ci->top = L->top + LUA_MINSTACK;
       ci->func = func;
-      L->ci = ci;
       lua_assert(ci->top <= L->stack_last);
       if (L->hookmask & LUA_MASKCALL) {
         int narg = cast_int(L->top - func) - 1;
@@ -486,18 +486,18 @@ void luaD_call (lua_State *L, StkId func, int nresults) {
       break;
     }
     case LUA_VLCL: {  /* Lua function */
-      CallInfo *ci = next_ci(L);
+      CallInfo *ci;
       Proto *p = clLvalue(s2v(func))->p;
       int narg = cast_int(L->top - func) - 1;  /* number of real arguments */
       int nfixparams = p->numparams;
       int fsize = p->maxstacksize;  /* frame size */
       checkstackp(L, fsize, func);
+      L->ci = ci = next_ci(L);
       ci->nresults = nresults;
       ci->u.l.savedpc = p->code;  /* starting point */
       ci->callstatus = 0;
       ci->top = func + 1 + fsize;
       ci->func = func;
-      L->ci = ci;
       for (; narg < nfixparams; narg++)
         setnilvalue(s2v(L->top++));  /* complete missing arguments */
       lua_assert(ci->top <= L->stack_last);
@@ -515,14 +515,13 @@ void luaD_call (lua_State *L, StkId func, int nresults) {
 
 /*
 ** Similar to 'luaD_call', but does not allow yields during the call.
-** If there is a stack overflow, freeing all CI structures will
-** force the subsequent call to invoke 'luaE_extendCI', which then
-** will raise any errors.
 */
 void luaD_callnoyield (lua_State *L, StkId func, int nResults) {
   incXCcalls(L);
-  if (getCcalls(L) <= CSTACKERR)  /* possible stack overflow? */
-    luaE_freeCI(L);
+  if (getCcalls(L) <= CSTACKERR) {  /* possible C stack overflow? */
+    luaE_exitCcall(L);  /* to compensate decrement in next call */
+    luaE_enterCcall(L);  /* check properly */
+  }
   luaD_call(L, func, nResults);
   decXCcalls(L);
 }
@@ -674,7 +674,7 @@ LUA_API int lua_resume (lua_State *L, lua_State *from, int nargs,
   if (from == NULL)
     L->nCcalls = CSTACKTHREAD;
   else  /* correct 'nCcalls' for this thread */
-    L->nCcalls = getCcalls(from) + from->nci - L->nci - CSTACKCF;
+    L->nCcalls = getCcalls(from) - L->nci - CSTACKCF;
   if (L->nCcalls <= CSTACKERR)
     return resume_error(L, "C stack overflow", nargs);
   luai_userstateresume(L, nargs);
--- a/src/lundump.c
+++ b/src/lundump.c
@@ -205,8 +205,9 @@ static void loadUpvalues (LoadState *S, Proto *f) {
   n = loadInt(S);
   f->upvalues = luaM_newvectorchecked(S->L, n, Upvaldesc);
   f->sizeupvalues = n;
-  for (i = 0; i < n; i++) {
+  for (i = 0; i < n; i++)
     f->upvalues[i].name = NULL;
+  for (i = 0; i < n; i++) {
     f->upvalues[i].instack = loadByte(S);
     f->upvalues[i].idx = loadByte(S);
     f->upvalues[i].kind = loadByte(S);
--- a/src/lvm.c
+++ b/src/lvm.c
@@ -1104,7 +1104,7 @@ void luaV_finishOp (lua_State *L) {
 
 
 #define checkGC(L,c)  \
-	{ luaC_condGC(L, L->top = (c),  /* limit of live values */ \
+	{ luaC_condGC(L, (savepc(L), L->top = (c)), \
                          updatetrap(ci)); \
            luai_threadyield(L); }
 
@@ -1792,8 +1792,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         vmbreak;
       }
       vmcase(OP_VARARGPREP) {
-        luaT_adjustvarargs(L, GETARG_A(i), ci, cl->p);
-        updatetrap(ci);
+        ProtectNT(luaT_adjustvarargs(L, GETARG_A(i), ci, cl->p));
         if (trap) {
           luaD_hookcall(L, ci);
           L->oldpc = pc + 1;  /* next opcode will be seen as a "new" line */
--- a/src/liolib.c
+++ b/src/liolib.c
@@ -279,6 +279,8 @@ static int io_popen (lua_State *L) {
   const char *filename = luaL_checkstring(L, 1);
   const char *mode = luaL_optstring(L, 2, "r");
   LStream *p = newprefile(L);
+  luaL_argcheck(L, ((mode[0] == 'r' || mode[0] == 'w') && mode[1] == '\0'),
+                   2, "invalid mode");
   p->f = l_popen(L, filename, mode);
   p->closef = &io_pclose;
   return (p->f == NULL) ? luaL_fileresult(L, 0, filename) : 1;

--- a/src/ldebug.c
+++ b/src/ldebug.c
@@ -188,8 +188,8 @@ static const char *upvalname (const Proto *p, int uv) {
 static const char *findvararg (CallInfo *ci, int n, StkId *pos) {
   if (clLvalue(s2v(ci->func))->p->is_vararg) {
     int nextra = ci->u.l.nextraargs;
-    if (n <= nextra) {
-      *pos = ci->func - nextra + (n - 1);
+    if (n >= -nextra) {  /* 'n' is negative */
+      *pos = ci->func - nextra - (n + 1);
       return "(vararg)";  /* generic name for any vararg */
     }
   }
@@ -202,7 +202,7 @@ const char *luaG_findlocal (lua_State *L, CallInfo *ci, int n, StkId *pos) {
   const char *name = NULL;
   if (isLua(ci)) {
     if (n < 0)  /* access to vararg values? */
-      return findvararg(ci, -n, pos);
+      return findvararg(ci, n, pos);
     else
       name = luaF_getlocalname(ci_func(ci)->p, n, currentpc(ci));
   }
@@ -783,11 +783,13 @@ l_noret luaG_runerror (lua_State *L, const char *fmt, ...) {
 ** previous instruction 'oldpc'.
 */
 static int changedline (const Proto *p, int oldpc, int newpc) {
+  if (p->lineinfo == NULL)  /* no debug information? */
+    return 0;
   while (oldpc++ < newpc) {
     if (p->lineinfo[oldpc] != 0)
       return (luaG_getfuncline(p, oldpc - 1) != luaG_getfuncline(p, newpc));
   }
-  return 0;  /* no line changes in the way */
+  return 0;  /* no line changes between positions */
 }
 
 
--- a/src/ldo.h
+++ b/src/ldo.h
@@ -44,7 +44,7 @@
 
 /* macro to check stack size and GC */
 #define checkstackGC(L,fsize)  \
-	luaD_checkstackaux(L, (fsize), (void)0, luaC_checkGC(L))
+	luaD_checkstackaux(L, (fsize), luaC_checkGC(L), (void)0)
 
 
 /* type of protected functions, to be ran by 'runprotected' */