This is expected. FunctionCallbackInfo instances are rarely constructed via
C++ `new`; instead they are usually created manually on the stack. So
adding a field to the class definition is going to be a lot of work, and
that field's type can't be a std::string -- it would have to be something
where you have precise control over the object layout.
I would suggest that you explore alternative approaches.
On Fri, Mar 27, 2020 at 6:21 AM L TY <n0b0dy...@gmail.com> wrote:
> Hi everyone,
>
> For some research reason, I need to log all property access to Blink in
> v8. Since all the property load information is passed to Blink through
> class `FunctionCallbackInfo`, I tried to add a pointer field in this class
> to hold the property name (represented as std::string) like follow:
>
> V8_INLINE FunctionCallbackInfo(internal::Address* implicit_args,
> internal::Address* values, int length);
> internal::Address* implicit_args_;
> internal::Address* values_;
> int length_;
> std::string* property_info_; // The field I add.
>
> }
>
> The `property_info_` field is initialized in the constructor function
> through c++ `new`.
> I also added a const setter function for the `property_info_` field. The
> setter function like follow:
>
> void FunctionCallbackInfo<T>::SetPropertyInfo(::std::string s) const {
> *property_info_ = s;
> }
>
> In Blink, I modified the template file to set this field every time an
> attribute in Blink is visited.
> In code snips I write by myself, it works well. However, when I try to
> run the code on some real-world websites, I found that the value of the
> field property_info_ is set to a strange value 0x38, so the pointer to the
> string is overlapped by some other value.
> I tried to mark the property_info_ field as private and even moved it to
> class `ReturnValue<T>`, the overlapping case still happens:
>
> template<typename T>
> class ReturnValue {
> public:
> template <class S> V8_INLINE ReturnValue(const ReturnValue<S>& that)
> : value_(that.value_) {
> TYPE_CHECK(T, S);
> }
> // Local setters
> template <typename S>
> V8_INLINE void Set(const Global<S>& handle);
> template <typename S>
> V8_INLINE void Set(const TracedGlobal<S>& handle);
> template <typename S>
> V8_INLINE void Set(const Local<S> handle);
> // Fast primitive setters
> V8_INLINE void Set(bool value);
> V8_INLINE void Set(double i);
> V8_INLINE void Set(int32_t i);
> V8_INLINE void Set(uint32_t i);
> // Fast JS primitive setters
> V8_INLINE void SetNull();
> V8_INLINE void SetUndefined();
> V8_INLINE void SetEmptyString();
> // Convenience getter for Isolate
> V8_INLINE Isolate* GetIsolate() const;
>
> // Pointer setter: Uncompilable to prevent inadvertent misuse.
> template <typename S>
> V8_INLINE void Set(S* whatever);
>
> // Getter. Creates a new Local<> so it comes with a certain performance
> // hit. If the ReturnValue was not yet set, this will return the
> undefined
> // value.
> V8_INLINE Local<Value> Get() const;
> // use for taint map by n0b0dy
> V8_INLINE internal::Address GetValueAddr() const;
>
> V8_INLINE void SetProperty(std::string) const; // The setter function I
> add
>
> private:
> template<class F> friend class ReturnValue;
> template<class F> friend class FunctionCallbackInfo;
> template<class F> friend class PropertyCallbackInfo;
> template <class F, class G, class H>
> friend class PersistentValueMapBase;
> V8_INLINE void SetInternal(internal::Address value) { *value_ = value; }
> V8_INLINE internal::Address GetDefaultValue();
> V8_INLINE explicit ReturnValue(internal::Address* slot);
> internal::Address* value_;
> internal::Address* property_info_; // the field I add
> };
>
>
>
> I read the in
> https://source.chromium.org/chromium/chromium/src/+/master:v8/src/builtins/x64/builtins-x64.cc;drc=34ad93361f96ad875bf350ced27e15b7aa126113;bpv=1;bpt=1;l=3317
> and found that v8 will arrange the stack frame with its own call
> convention, But I didn't find why the pointer value is still overlapped in
> class ReturnValue.
>
> Does anyone have ideas about what should I do?
>
> Thanks a lot!
>
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