+Leszek Swirski <lesz...@google.com>
I am unsure what impact lazy compilation has here. There might be a weird
interaction with the stack frame cache. Does the flag "--optimize-for-size"
cause any change in the result? That flag disables the stack frame cache
(among other things).
On Tue, Nov 19, 2019 at 8:37 AM Darin Dimitrov <darin.dimit...@gmail.com>
wrote:
> Further narrowed it down to the "--no-lazy" runtime flag:
>
> Working:
>
> std::string flags = "--expose_gc --jitless";
> V8::SetFlagsFromString(flags.c_str(), flags.size());
>
> NOT working:
>
> std::string flags = "--expose_gc --jitless --no-lazy";
> V8::SetFlagsFromString(flags.c_str(), flags.size());
>
> Any idea why would the --no-lazy flag affect function names in stack
> frames? I need the --no-lazy flag because I noticed that it speeds up code
> cached scripts (v8::ScriptCompiler::CreateCodeCache API).
>
> On Tuesday, November 19, 2019 at 9:30:07 AM UTC+2, Darin Dimitrov wrote:
>>
>> Simon, thanks for the clarification. Does this mean that there's no
>> reliable way to get this information with the current V8 public API?
>>
>> I went ahead and wrote a simple example illustrating the issue and tried
>> running it on different platforms. And the results were surprising.
>>
>> Here's the sample code I wrote:
>>
>> Isolate::CreateParams create_params;
>> create_params.array_buffer_allocator = &allocator_;
>> Isolate* isolate = Isolate::New(create_params);
>> Isolate::Scope isolate_scope(isolate);
>> HandleScope handle_scope(isolate);
>> Local<ObjectTemplate> globalTemplate = ObjectTemplate::New(isolate);
>> Local<Context> context = Context::New(isolate, nullptr,
>> globalTemplate);
>> context->Enter();
>>
>> Local<v8::Function> captureFunc = v8::Function::New(context, [](const
>> FunctionCallbackInfo<Value>& info) {
>> Isolate* isolate = info.GetIsolate();
>> Local<Context> context = isolate->GetCurrentContext();
>> Local<Object> exception =
>> Exception::Error(v8::String::NewFromUtf8(isolate, "",
>> NewStringType::kNormal, 0).ToLocalChecked()).As<Object>();
>> Local<Value> stackProperty = exception->Get(context,
>> v8::String::NewFromUtf8(isolate, "stack", NewStringType::kNormal,
>> 5).ToLocalChecked()).ToLocalChecked();
>> v8::String::Utf8Value stackStr(isolate, stackProperty);
>> printf("%s\n\n", *stackStr);
>>
>> Local<StackTrace> stack =
>> v8::StackTrace::CurrentStackTrace(isolate, 10,
>> v8::StackTrace::StackTraceOptions::kDetailed);
>>
>> for (int i = 0; i < stack->GetFrameCount(); i++) {
>> Local<v8::StackFrame> frame = stack->GetFrame(isolate, i);
>> Local<v8::String> funcName = frame->GetFunctionName();
>> v8::String::Utf8Value str(isolate, funcName);
>> const char* name = *str;
>> printf("%s (%d:%d)\n", name, frame->GetLineNumber(),
>> frame->GetColumn());
>> }
>> }).ToLocalChecked();
>> assert(context->Global()->Set(context,
>> v8::String::NewFromUtf8(isolate, "captureTrace", NewStringType::kNormal,
>> 12).ToLocalChecked(), captureFunc).FromMaybe(false));
>>
>> std::string src =
>> "(function test() {"
>> " const viewModel = new Object();"
>> " viewModel.onTap = () => { captureTrace(); };"
>> " viewModel.onTap.apply(viewModel, []);"
>> "})();";
>> Local<Script> script = Script::Compile(context,
>> v8::String::NewFromUtf8(isolate, src.c_str(), NewStringType::kNormal,
>> (int)src.length()).ToLocalChecked()).ToLocalChecked();
>> Local<Value> result;
>> assert(script->Run(context).ToLocal(&result));
>>
>> On V8 8.0.0 (
>> https://chromium.googlesource.com/v8/v8.git/+/50031fae736fac7b2b309369df492bfd0edd7553),
>> running in --jitless on an arm64 iOS device, I get the following output:
>>
>> Error
>> at Object.onTap (<anonymous>:1:84)
>> at test (<anonymous>:1:122)
>> at <anonymous>:1:145
>>
>> (null) (1:84)
>> test (1:122)
>> (null) (1:145)
>>
>> and on V8 7.7.299.11 (
>> https://chromium.googlesource.com/v8/v8.git/+/027689dbfcb2a9bbc8ceec4db2631c558e879633),
>> running on an arm64 Android device, I get the following output:
>>
>> Error
>> at Object.viewModel.onTap (<anonymous>:1:84)
>> at test (<anonymous>:1:122)
>> at <anonymous>:1:145
>>
>> viewModel.onTap (1:84)
>> test (1:122)
>> (null) (1:145)
>>
>> Do you know what might explain the discrepancy between those two
>> platforms?
>>
>> On Tuesday, November 19, 2019 at 7:58:10 AM UTC+2, Simon Zünd wrote:
>>>
>>> This is a bug in our API implementation. Or better, there is a mismatch
>>> between API and what we do internally. "Method names" and "class names" are
>>> stored separately from function names. This can be seen here, when we
>>> collect all the information for a single frame:
>>> https://cs.chromium.org/chromium/src/v8/src/heap/factory.cc?rcl=e1eb815647f334a8cf970439343a8febfa9f6d11&l=3732
>>>
>>> There is really no reason why this information shouldn't be made
>>> available in the API. The only tricky thing is to come up with a better
>>> API, as some of the getters change meaning depending whether its a JS or
>>> WASM frame and I am not really happy with the current solution.
>>>
>>> On Mon, Nov 18, 2019 at 4:40 PM Darin Dimitrov <darin....@gmail.com>
>>> wrote:
>>>
>>>> I am embedding V8 and trying to capture the current javascript
>>>> stacktrace using the "v8::StackTrace::CurrentStackTrace":
>>>>
>>>> Isolate* isolate = info.GetIsolate();
>>>>
>>>> Local<StackTrace> stack = v8::StackTrace::CurrentStackTrace(isolate, 10,
>>>> v8::StackTrace::StackTraceOptions::kDetailed);
>>>>
>>>> *for* (*int* i = 0; i < stack->GetFrameCount(); i++) {
>>>>
>>>> Local<v8::StackFrame> frame = stack->GetFrame(isolate, i);
>>>>
>>>> Local<v8::String> funcName = frame->GetFunctionName();
>>>>
>>>> v8::String::Utf8Value str(isolate, funcName);
>>>>
>>>> *const* *char** name = *str;
>>>>
>>>> printf("%s (%d:%d)\n", name, frame->GetLineNumber(), frame->
>>>> GetColumn());
>>>>
>>>> }
>>>>
>>>> I have placed this code inside a custom function that I have registered
>>>> to the global scope.
>>>>
>>>> Before calling my custom function, I tried logging the stack property
>>>> of an Error object (by using : console.log(new Error().stack)) and I
>>>> obtained the following output:
>>>>
>>>> Error
>>>> at bar (file:///app/bundle.js:266:29)
>>>> at test (file:///app/bundle.js:267:15)
>>>> at Observable.onTap (file:///app/bundle.js:268:11)
>>>> at Button.notify (file:///app/vendor.js:3620:32)
>>>> at Button._emit (file:///app/vendor.js:3640:18)
>>>> at TapHandlerImpl.tap (file:///app/vendor.js:15540:19)
>>>>
>>>> With the "v8::StackTrace::CurrentStackTrace" method I get:
>>>>
>>>> bar (266:29)
>>>> test (267:15)
>>>> (null) (268:11)
>>>> (null) (3620:32)
>>>> (null) (3640:18)
>>>> (null) (15540:19)
>>>>
>>>> I am getting empty function names from some frames, while all the other
>>>> information is present (script name, line, column numbers, ...).
>>>>
>>>> Do you know what might be the reason for getting empty function names?
>>>>
>>>> --
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>>>> .
>>>>
>>>
>>
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