Upvalues Overwritten

Bug Reports Engine Bugs
#1

Causing any ‘Lua’ error (not from ROBLOX libraries or error functions) will overwrite every upvalue to some weird values. Usually numbers, threads and nil; depending on where the upvalue was indexed.

Reproduction code:

local x = "Hi"
coroutine.resume(coroutine.create(function()
	while wait() do
		print(x)
	end
end))
a()

Output:
> error: attempt to call global 'a' (a nil value)
> 367
> 367
> 367
> 367
...

This is not a new bug. I went through this problem 1 year ago but didn’t know the exact cause. So far I see no harm for this behavior and can be useful for ugly hacks. But still it shouldn’t be happening.

Note that it only occurs online and from a script (not from developer console).

How does spoofing upvalues work exactly?
#2

I have to say, that looks like a really neat bug. Never ran into it myself, however.

#3

I like to think I can rationalize how most bugs might happen, but this one… not really.

I’ll try and repro when I’m on my PC.

#4

Just tested and apparently it resets the values to nil after 3-4 seconds. Very strange indeed.

#5

This… apparently… is what happens when somebody decides to randomly call lua_settop(thread, 0) without considering the consequences. We’ll fix this.

1 Like
#6

I think I bumped into this before but wasn’t able to get a good simple repro.

Good see it’s getting looked at.

#7

I could be running into the same issue here, Not sure.

EDIT:

I indeed was running into the same issue :slight_smile:

#8

This should be fixed now.