The --optimize-for-size flag doesn't seem to have any effect on the result.
On Tuesday, November 19, 2019 at 9:50:33 AM UTC+2, Simon Zünd wrote:
>
> +Leszek Swirski <javascript:>
>
> 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....@gmail.com
> <javascript:>> 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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>
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