Change lua_pushlightuserdata API usage in OpenResty

zhongwei.yao · 2016-11-15T12:01:16+00:00

Hi,How easy/hard would it be to modify Test::Nginx::Socket so that it could make remote requests with its HTTP client instead of spinning up a local nginx se...

Change lua_pushlightuserdata API usage in OpenResty

zhongwei.yao

Hi, all,

I find OpenResty core tests crash on Linux machine with 48-bit virtual address. (My environment is 48-bit ARM64 Linux)

It is because LuaJIT will fail when using light userdata under 48-bit virtual address system in some cases. I proposed a work around [0] in LuaJIT to fix this issue, but LuaJIT upstream thinks this issue is better to fix in LuaJIT application rather LuaJIT itself [1].

So with following modification to the usage of lua_pushlightuserdata API in OpenResty, this issue could be solved (suggests from [1]):

lightuserdata used as a unique table key, e.g. for the registry: with lua_pushlightuserdata(L, &x)and x on the C stack, replace x with a static variable.
lightuserdata used as some kind of cross-object pointer: don't do that -- it doesn't play nicely with the GC, anyway. Replace with proper userdata references.
lightuserdata used as a misguided userdata replacement, possibly even setting the lightuserdata metatable (ugh): throw away any such library, replace with a proper FFI binding.

Do you think such modification is OK to OpenResty and will you fix it in OpenResty?

[0]: http://www.freelists.org/post/luajit/fix-lightud-type-for-48bit-virtual-address

[1]: https://github.com/LuaJIT/LuaJIT/pull/230#issuecomment-260205661

Best regards,

Zhongwei

agentzh

Hello!

On Mon, Nov 14, 2016 at 8:01 PM, Zhongwei Yao wrote:
> It is because LuaJIT will fail when using light userdata under 48-bit
> virtual address system in some cases. I proposed a work around [0] in LuaJIT
> to fix this issue, but LuaJIT upstream thinks this issue is better to fix in
> LuaJIT application rather LuaJIT itself [1].
>
[...]
>
> Do you think such modification is OK to OpenResty and will you fix it in
> OpenResty?
>

Yeah, getting the LuaJIT's new GC64 mode actually work with OpenResty
should be very interesting. You're welcome to create pull requests to
make any necessary changes in the ngx_lua module and etc. Then we'd
love to have a look at your patches :)

Thanks!
-agentzh