I'm working on a research project that adds instrumentation code to Blink
and V8. As part of that instrumentation, I want to get the script ID of the
currently executing script from the Isolate while the script is executing,
and how I'm doing this is (in isolate.cc):
```
int Isolate::GetScriptId() {
JavaScriptFrameIterator it(this);
while (!it.done()) {
JavaScriptFrame* frame = it.frame();
Handle<JSFunction> function(frame->function(), this);
Object maybe_script = function->shared().script();
if (!maybe_script.IsScript()) {
it.Advance();
continue;
}
Script script = Script::cast(maybe_script);
return script.id();
}
}
```
Then I call this from various places in Blink code. One such place is
`StorageArea::getItem`
(third_party/blink/renderer/modules/storage/storage_area.cc) to record
which script called getItem.
This normally works fine, but for one particular script on one particular
website, I get an empty stack (i.e. JavaScriptFrameIterator `it.done()` is
true right after instantiation). This is the output of `PrintStack(stdout,
Isolate::kPrintStackConcise)`:
```
==== JS stack trace =========================================
0: ExitFrame [pc: 0x10f5993bf]
1: StubFrame [pc: 0x10f6dbf1b]
Security context: 0x001e08333019 <String[#47]:
https://hbr.org978B69E968F091D0A4963181648E7306>
2: /* anonymous */(aka /* anonymous */)
[0x1e081af4c9](this=0x001e0804030d <undefined>,0x001e08b4ee41 <Storage map
= 0x1e082e6191>#0#)
3: StubFrame [pc: 0x10f6d8894]
4: StubFrame [pc: 0x10f40b328]
5: EntryFrame [pc: 0x10f371d58]
=====================
```
I realize this is a bit involved: and relates to both Blink and V8, just
wondering if anyone knows why this might be the case or have any tips for
debugging.
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