Re: A crash in Lua 5.3.2

[Roberto Ierusalimschy <roberto@...>]

> > ```
> > local mt = {}
> > mt.__newindex = mt
> > local t = setmetatable({}, mt)
> > t[1] = 1
> > ```
> 
> Right :-(  Thanks for the report. Probably it was introduced with the
> optimizations on table operations; it does not happen in 5.3.1.

The bug is quite subtle. Follows a fix:

diff for lvm.c:
----------------------------------------
193c193,194
<       lua_assert(ttistable(t) && ttisnil(oldval));
---
>       Table *h = hvalue(t);
>       lua_assert(ttisnil(oldval));
195c196
<       if ((tm = fasttm(L, hvalue(t)->metatable, TM_NEWINDEX)) == NULL &&
---
>       if ((tm = fasttm(L, h->metatable, TM_NEWINDEX)) == NULL &&
200c201
<          (oldval = luaH_newkey(L, hvalue(t), key), 1))) {
---
>          (oldval = luaH_newkey(L, h, key), 1))) {
203,204c204,205
<         invalidateTMcache(hvalue(t));
<         luaC_barrierback(L, hvalue(t), val);
---
>         invalidateTMcache(h);
>         luaC_barrierback(L, h, val);
----------------------------------------

-- Roberto