[webkit-dev] Can we drop supporting mixed Wasm::MemoryMode in one process?

Yusuke Suzuki yusukesuzuki at slowstart.org
Tue Aug 28 11:21:10 PDT 2018

Posted this mail to webkit-dev mailing list too :)

On Wed, Aug 29, 2018 at 3:19 AM Yusuke Suzuki <yusukesuzuki at slowstart.org>

> Hi JSC folks,
> In Wasm supported environment, our MemoryMode is a bit dynamic.
> When we fail to allocate WasmMemory for signaling mode, we fall back to
> the bound checking memory instead.
> But Wasm code compiled for signaling / bound checking is incompatible. If
> the code is compiled
> as signaling mode, and if we attach the memory for bound checking, we need
> to recompile the
> code for bound checking mode. This introduces significant complexity to
> our wasm compilation.
> And our WebAssembly.compile is not basically compiling: it is just
> validating.
> Actual compiling needs to be deferred until the memory is attached by
> instantiating.
> It is not good when we would like to share WasmModule among multiple wasm
> threads / workers in the future, since the "compiled" Wasm module is not
> actually compiled.
> So, my proposal is, can we explore the way to exclusively support one of
> MemoryMode in a certain architecture?
> For example, in x64, enable signaling mode, and we report OOM errors if we
> fail to allocate WasmMemory with signaling mode.
> Best regards,
> Yusuke Suzuki
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