Previously the Debug Proxy API that's exposed on Wasm frames by
Runtime.evaluateOnCallFrame() was implemented via actual JSProxy
instances. That means that all entities such as "memories", "tables",
"stack", "globals", etc. were JSProxy instances with "get" and "has"
traps. But that has a couple of down-sides:
1. In DevTools front-end, the proxies are shown as JSProxy, which is not
very useful to developers, since they cannot interact with them nor
can they inspect their contents. And the object preview also only
shows "Proxy {}" for them.
2. The performance doesn't scale well, which becomes a painful
bottleneck with larger Wasm modules that contain hundreds of
thousands of functions or globals.
3. We cannot use the JSProxy instances in the Scope view (for the
reasons outlined in 1.) and hence we have different logic to provide
Scope values than values in the rest of DevTools, which led to subtle
but annoying bugs and inconsistencies.
This also changes the "locals" implementation by querying the values
ahead of time, similar to the object exposed to the Scope view, instead
of on-demand, since the "locals" object might survive the current
debugger pause and peeking into the stack afterwards would read invalid
memory (and might even be a security issue). For being able to change
locals we need to look into a similar solution as what we have for
JavaScript locals already. The expression stack already works this way.
For performance reasons (especially scaling to huge, realistic Wasm
modules), we cache the per-instance proxies ("functions", "memories",
"tables" and "globals") on the WasmInstanceObject and reuse them (which
is safe since they have a `null` prototype and are non-extensible), and
we also cache the proxy maps (with the interceptors) on the
JSGlobalObject per native context.
Doc: http://bit.ly/devtools-wasm-entities
Bug: chromium:1127914, chromium:1159402, chromium:1071432, chromium:1164241
Change-Id: I6191035fdfd887835ae533fcdaabb5bbc8e661ae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2606058
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71981}
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