QuickJS breaks on OOM in a vm

[vicrazumov]

Hi @justjake

When a vm fails due to the "out of memory" issue, I cannot neither dispose it nor create a new one. It keeps failing with the RuntimeError: memory access out of bounds.

How to reproduce

1. run vm.evalScript() with a code, big enough to violate the memory limit
2. you will get the RuntimeError: memory access out of bounds error
3. try calling vm.dispose() or quickJS.createVm() - you will be getting the same error

[justjake]

Hi @vicrazumov, thanks for reporting this issue. I’m curious about the specifics of your case, some more information or even a failing test would help debug this.

• what runtime environment (Chrome? Node, node version?)
• what memory limit do you set?
• what do you mean by “big enough code”? Do you mean a large script string, or a script that allocates many bytes?

Help reproducing would be appreciated 😄

[vicrazumov]

Hi @justjake

Sorry, should have made it more clear.

1. Chrome
2. I haven't set it explicitly
3. I meant a large script string (my code had a 1+ MB JSON object)

You can try here - replace the 400 + 20 with a big JSON (you can generate one here - use at least 1000 rows)

[justjake]

Okay, after some research, I've determined that this issue is because Emscripten's built-in C FFI passes function arguments on the stack, and doesn't resize the stack even when an argument is very large. Details in this 2018 github issue: emscripten-core/emscripten#6860 (comment)

The issue occurs for any FFI function passed a 1MB string, even for no-op functions.

The solution is to switch to passing heap-allocated strings to our FFI functions if the strings are large.

[justjake]

fix published in https://www.npmjs.com/package/quickjs-emscripten/v/0.11.0