We introduce a wasm null object, separate from JS null. Its purpose is
to support trapping null accesses for wasm objects.
This will be achieved by allocating a large payload for it (larger than
any wasm struct) and memory-protecting it (see linked CL). The two null
objects get mapped to each other at the wasm-JS boundary.
Since externref objects live on the JS side of the boundary,
null-related instructions in wasm now need an additional type argument
to handle the correct null object.
Bug: v8:7748
Change-Id: I06da00fcd279cc5376e69ab7858e3782f5b5081e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4200639
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#85648}
2e357c4814