<
      luaA_pushobject(L, ci->base + (n - 1));
  lua_unlock(L);
  return name;
}


LUA_API const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n) {
  CallInfo *ci = L->base_ci + ar->i_ci;
  const char *name = findlocal(L, ci, n);
  lua_lock(L);
  if (name)
      setobjs2s(L, ci->base + (n - 1), L->top - 1);
  L->top--;  /* pop value */
  lua_unlock(L);
  return name;
}


static void funcinfo (lua_Debug *ar, Closure *cl) {
  if (cl->c.isC) {
    ar->source = "=[C]";
    ar->linedefined = -1;
    ar->lastlinedefined = -1;
    ar->what = "C";
  }
  else {
    ar->source = getstr(cl->l.p->source);
    ar->linedefined = cl->l.p->linedefined;
    ar->lastlinedefined = cl->l.p->lastlinedefined;
    ar->what = (ar->linedefined == 0) ? "main" : "Lua";
  }
  luaO_chunkid(ar->short_src, ar->source, LUA_IDSIZE);
}


static void info_tailcall (lua_Debug *ar) {
  ar->name = ar->namewhat = "";
  ar->what = "tail";
  ar->lastlinedefined = ar->linedefined = ar->currentline = -1;
  ar->source = "=(tail call)";
  luaO_chunkid(ar->short_src, ar->source, LUA_IDSIZE);
  ar->nups = 0;
}


static void collectvalidlines (lua_State *L, Closure *f) {
  if (f == NULL || f->c.isC) {
    setnilvalue(L->top);
  }
  else {
    Table *t = luaH_new(L, 0, 0);
    int *lineinfo = f->l.p->lineinfo;
    int i;
    for (i=0; i<f->l.p->sizelineinfo; i++)
      setbvalue(luaH_setnum(L, t, lineinfo[i]), 1);
    sethvalue(L, L->top, t); 
  }
  incr_top(L);
}


static int auxgetinfo (lua_State *L, const char *what, lua_Debug *ar,
                    Closure *f, CallInfo *ci) {
  int status = 1;
  if (f == NULL) {
    info_tailcall(ar);
    return status;
  }
  for (; *what; what++) {
    switch (*what) {
      case 'S': {
        funcinfo(ar, f);
        break;
      }
      case 'l': {
        ar->currentline = (ci) ? currentline(L, ci) : -1;
        break;
      }
      case 'u': {
        ar->nups = f->c.nupvalues;
        break;
      }
      case 'n': {
        ar->namewhat = (ci) ? getfuncname(L, ci, &ar->name) : NULL;
        if (ar->namewhat == NULL) {
          ar->namewhat = "";  /* not found */
          ar->name = NULL;
        }
        break;
      }
      case 'L':
      case 'f':  /* handled by lua_getinfo */
        break;
      default: status = 0;  /* invalid option */
    }
  }
  return status;
}


LUA_API int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar) {
  int status;
  Closure *f = NULL;
  CallInfo *ci = NULL;
  lua_lock(L);
  if (*what == '>') {
    StkId func = L->top - 1;
    luai_apicheck(L, ttisfunction(func));
    what++;  /* skip the '>' */
    f = clvalue(func);
    L->top--;  /* pop function */
  }
  else if (ar->i_ci != 0) {  /* no tail call? */
    ci = L->base_ci + ar->i_ci;
    lua_assert(ttisfunction(ci->func));
    f = clvalue(ci->func);
  }
  status = auxgetinfo(L, what, ar, f, ci);
  if (strchr(what, 'f')) {
    if (f == NULL) setnilvalue(L->top);
    else setclvalue(L, L->top, f);
    incr_top(L);
  }
  if (strchr(what, 'L'))
    collectvalidlines(L, f);
  lua_unlock(L);
  return status;
}


/*
** {======================================================
** Symbolic Execution and code checker
** =======================================================
*/

#define check(x)		if (!(x)) return 0;

#define checkjump(pt,pc)	check(0 <= pc && pc < pt->sizecode)

#define checkreg(pt,reg)	check((reg) < (pt)->maxstacksize)



static int precheck (const Proto *pt) {
  check(pt->maxstacksize <= MAXSTACK);
  check(pt->numparams+(pt->is_vararg & VARARG_HASARG) <= pt->maxstacksize);
  check(!(pt->is_vararg & VARARG_NEEDSARG) ||
              (pt->is_vararg & VARARG_HASARG));
  check(pt->sizeupvalues <= pt->nups);
  check(pt->sizelineinfo == pt->sizecode || pt->sizelineinfo == 0);
  check(pt->sizecode > 0 && GET_OPCODE(pt->code[pt->sizecode-1]) == OP_RETURN);
  return 1;
}


#define checkopenop(pt,pc)	luaG_checkopenop((pt)->code[(pc)+1])

int luaG_checkopenop (Instruction i) {
  switch (GET_OPCODE(i)) {
    case OP_CALL:
    case OP_TAILCALL:
    case OP_RETURN:
    case OP_SETLIST: {
      check(GETARG_B(i) == 0);
      return 1;
    }
    default: return 0;  /* invalid instruction after an open call */
  }
}


static int checkArgMode (const Proto *pt, int r, enum OpArgMask mode) {
  switch (mode) {
    case OpArgN: check(r == 0); break;
    case OpArgU: break;
    case OpArgR: checkreg(pt, r); break;
    case OpArgK:
      check(ISK(r) ? INDEXK(r) < pt->sizek : r < pt->maxstacksize);
      break;
  }
  return 1;
}


static Instruction symbexec (const Proto *pt, int lastpc, int reg) {
  int pc;
  int last;  /* stores position of last instruction that changed `reg' */
  last = pt->sizecode-1;  /* points to final return (a `neutral' instruction) */
  check(precheck(pt));
  for (pc = 0; pc < lastpc; pc++) {
    Instruction i = pt->code[pc];
    OpCode op = GET_OPCODE(i);
    int a = GETARG_A(i);
    int b = 0;
    int c = 0;
    check(op < NUM_OPCODES);
    checkreg(pt, a);
    switch (getOpMode(op)) {
      case iABC: {
        b = GETARG_B(i);
        c = GETARG_C(i);
        check(checkArgMode(pt, b, getBMode(op)));
        check(checkArgMode(pt, c, getCMode(op)));
        break;
      }
      case iABx: {
        b = GETARG_Bx(i);
        if (getBMode(op) == OpArgK) check(b < pt->sizek);
        break;
      }
      case iAsBx: {
        b = GETARG_sBx(i);
        if (getBMode(op) == OpArgR) {
          int dest = pc+1+b;
          check(0 <= dest && dest < pt->sizecode);
          if (dest > 0) {
            int j;
            /* check that it does not jump to a setlist count; this
               is tricky, because the count from a previous setlist may
               have the same value of an invalid setlist; so, we must
               go all the way back to the first of them (if any) */
            for (j = 0; j < dest; j++) {
              Instruction d = pt->code[dest-1-j];
              if (!(GET_OPCODE(d) == OP_SETLIST && GETARG_C(d) == 0)) break;
            }
            /* if 'j' is even, previous value is not a setlist (even if
               it looks like one) */
            check((j&1) == 0);
          }
        }
        break;
      }
    }
    if (testAMode(op)) {
      if (a == reg) last = pc;  /* change register `a' */
    }
    if (testTMode(op)) {
      check(pc+2 < pt->sizecode);  /* check skip */
      check(GET_OPCODE(pt->code[pc+1]) == OP_JMP);
    }
    switch (op) {
      case OP_LOADBOOL: {
        if (c == 1) {  /* does it jump? */
          check(pc+2 < pt->sizecode);  /* check its jump */
          check(GET_OPCODE(pt->code[pc+1]) != OP_SETLIST ||
                GETARG_C(pt->code[pc+1]) != 0);
        }
        break;
      }
      case OP_LOADNIL: {
        if (a <= reg && reg <= b)
          last = pc;  /* set registers from `a' to `b' */
        break;
      }
      case OP_GETUPVAL:
      case OP_SETUPVAL: {
        check(b < pt->nups);
        break;
      }
      case OP_GETGLOBAL:
      case OP_SETGLOBAL: {
        check(ttisstring(&pt->k[b]));
        break;
      }
      case OP_SELF: {
        checkreg(pt, a+1);
        if (reg == a+1) last = pc;
        break;
      }
      case OP_CONCAT: {
        check(b < c);  /* at least two operands */
        }
      default: break;
    }
  }
  return pt->code[last];
}

#undef check
#undef checkjump
#undef checkreg

/* }====================================================== */


int luaG_checkcode (const Proto *pt) {
  return (symbexec(pt, pt->sizecode, NO_REG) != 0);
}


static const char *kname (Proto *p, int c) {
  if (ISK(c) && ttisstring(&p->k[INDEXK(c)]))
    return svalue(&p->k[INDEXK(c)]);
  else
    return "?";
}


static const char *getobjname (lua_State *L, CallInfo *ci, int stackpos,
                               const char **name) {
  if (isLua(ci)) {  /* a Lua function? */
    Proto *p = ci_func(ci)->l.p;
    int pc = currentpc(L, ci);
    Instruction i;
    *name = luaF_getlocalname(p, stackpos+1, pc);
    if (*name)  /* is a local? */
      return "local";
    i = symbexec(p, pc, stackpos);  /* try symbolic execution */
    lua_assert(pc != -1);
    switch (GET_OPCODE(i)) {
      case OP_GETGLOBAL: {
        int g = GETARG_Bx(i);  /* global index */
        lua_assert(ttisstring(&p->k[g]));
        *name = svalue(&p->k[g]);
        return "global";
      }
      case OP_MOVE: {
        int a = GETARG_A(i);
        int b = GETARG_B(i);  /* move from `b' to `a' */
        if (b < a)
          return getobjname(L, ci, b, name);  /* get name for `b' */
        break;
      }
      case OP_GETTABLE: {
        int k = GETARG_C(i);  /* key index */
        *name = kname(p, k);
        return "field";
      }
      case OP_GETUPVAL: {
        int u = GETARG_B(i);  /* upvalue index */
        *name = p->upvalues ? getstr(p->upvalues[u]) : "?";
        return "upvalue";
      }
      case OP_SELF: {
        int k = GETARG_C(i);  /* key index */
        *name = kname(p, k);
        return 
      GET_OPCODE(i) == OP_TFORLOOP)
    return getobjname(L, ci, GETARG_A(i), name);
  else
    return NULL;  /* no useful name can be found */
}


/* only ANSI way to check whether a pointer points to an array */
static int isinstack (CallInfo *ci, const TValue *o) {
  StkId p;
  for (p = ci->base; p < ci->top; p++)
    if (o == p) return 1;
  return 0;
}


void luaG_typeerror (lua_State *L, const TValue *o, const char *op) {
  const char *name = NULL;
  const char *t = luaT_typenames[ttype(o)];
  const char *kind = (isinstack(L->ci, o)) ?
                         getobjname(L, L->ci, cast_int(o - L->base), &name) :
                         NULL;
  if (kind)
    luaG_runerror(L, "attempt to %s %s " LUA_QS " (a %s value)",
                op, kind, name, t);
  else
    luaG_runerror(L, "attempt to %s a %s value", op, t);
}


void luaG_concaterror (lua_State *L, StkId p1, StkId p2) {
  if (ttisstring(p1) || ttisnumber(p1)) p1 = p2;
  lua_assert(!ttisstring(p1) && !ttisnumber(p1));
  luaG_typeerror(L, p1, "concatenate");
}


void luaG_aritherror (lua_State *L, const TValue *p1, const TValue *p2) {
  TValue temp;
  if (luaV_tonumber(p1, &temp) == NULL)
    p2 = p1;  /* first operand is wrong */
  luaG_typeerror(L, p2, "perform arithmetic on");
}


int luaG_ordererror (lua_State *L, const TValue *p1, const TValue *p2) {
  const char *t1 = luaT_typenames[ttype(p1)];
  const char *t2 = luaT_typenames[ttype(p2)];
  if (t1[2] == t2[2])
    luaG_runerror(L, "attempt to compare two %s values", t1);
  else
    luaG_runerror(L, "attempt to compare %s with %s", t1, t2);
  return 0;
}


static void addinfo (lua_State *L, const char *msg) {
  CallInfo *ci = L->ci;
  if (isLua(ci)) {  /* is Lua code? */
    char buff[LUA_IDSIZE];  /* add file:line information */
    int line = currentline(L, ci);
    luaO_chunkid(buff, getstr(getluaproto(ci)->source), LUA_IDSIZE);
    luaO_pushfstring(L, "%s:%d: %s", buff, line, msg);
  }
}


void luaG_errormsg (lua_State *L) {
  if (L->errfunc != 0) {  /* is there an error handling function? */
    StkId errfunc = restorestack(L, L->errfunc);
    if (!ttisfunction(errfunc)) luaD_throw(L, LUA_ERRERR);
    setobjs2s(L, L->top, L->top - 1);  /* move argument */
    setobjs2s(L, L->top - 1, errfunc);  /* push function */
    incr_top(L);
    luaD_call(L, L->top - 2, 1);  /* call it */
  }
  luaD_throw(L, LUA_ERRRUN);
}


void luaG_runerror (lua_State *L, const char *fmt, ...) {
  va_list argp;
  va_start(argp, fmt);
  addinfo(L, luaO_pushvfstring(L, fmt, argp));
  va_end(argp);
  luaG_errormsg(L);
}