In a C++/CLI assembly, I'm trying to call a managed delegate from a native callback. I followed Doc Brown's answer here, and my implementation so far looks like this:
The native callback - ignore the commented out parts for now:
static ssize_t idaapi idb_callback(void* user_data, int notification_code, va_list va)
{
switch (notification_code)
{
case idb_event::byte_patched:
{
//ea_t address = va_arg(va, ea_t);
//uint32 old_value = va_arg(va, uint32);
return IdaEvents::BytePatched(0, 0);
}
break;
}
return 0;
}
As you can see above, I call this managed delegate instantiated in a static class:
public delegate int DatabaseBytePatchedHandler(int address, int originalValue);
private ref class IdaEvents
{
static IdaEvents()
{
BytePatched = gcnew DatabaseBytePatchedHandler(&OnDatabaseBytePatched);
}
public: static DatabaseBytePatchedHandler^ BytePatched;
private: static int OnDatabaseBytePatched(int address, int originalValue)
{
return 0;
}
};
This compiles fine. But the code is incomplete - remember the commented out part in the native callback above? I actually have to retrieve the values from the va_list passed to the callback, and pass those on to my managed delegate:
ea_t address = va_arg(va, ea_t);
uint32 old_value = va_arg(va, uint32);
return IdaEvents::BytePatched(address, old_value);
But as soon as I uncomment one of the lines using va_arg, I cannot compile the project anymore and retrieve the following errors marking the line where I call the managed delegate:
C3821 'IdaEvents': managed type or function cannot be used in an unmanaged function
C3821 'IdaEvents::BytePatched': managed type or function cannot be used in an unmanaged function
C3821 'BytePatched': managed type or function cannot be used in an unmanaged function
C3821 'DatabaseBytePatchedHandler::Invoke': managed type or function cannot be used in an unmanaged function
C3642 'int DatabaseBytePatchedHandler::Invoke(int,int)': cannot call a function with __clrcall calling convention from native code
C3175 'DatabaseBytePatchedHandler::Invoke': cannot call a method of a managed type from unmanaged function 'idb_callback'
This really confuses me. Why is the compiler suddenly acting up as soon as I try to use va_arg? Even a single line without any assignment causes this error to pop up.
Am I thinking too naive here? I'm obviously missing a piece of the puzzle, and any help supporting me in finding it is greatly appreciated.
Related
Im trying to load my model in my controller and tried this:
return Post::getAll();
got the error Non-static method Post::getAll() should not be called statically, assuming $this from incompatible context
The function in the model looks like this:
public function getAll()
{
return $posts = $this->all()->take(2)->get();
}
What's the correct way to load the model in a controller and then return it's contents?
You defined your method as non-static and you are trying to invoke it as static. That said...
1.if you want to invoke a static method, you should use the :: and define your method as static.
// Defining a static method in a Foo class.
public static function getAll() { /* code */ }
// Invoking that static method
Foo::getAll();
2.otherwise, if you want to invoke an instance method you should instance your class, use ->.
// Defining a non-static method in a Foo class.
public function getAll() { /* code */ }
// Invoking that non-static method.
$foo = new Foo();
$foo->getAll();
Note: In Laravel, almost all Eloquent methods return an instance of your model, allowing you to chain methods as shown below:
$foos = Foo::all()->take(10)->get();
In that code we are statically calling the all method via Facade. After that, all other methods are being called as instance methods.
Why not try adding Scope? Scope is a very good feature of Eloquent.
class User extends Eloquent {
public function scopePopular($query)
{
return $query->where('votes', '>', 100);
}
public function scopeWomen($query)
{
return $query->whereGender('W');
}
}
$users = User::popular()->women()->orderBy('created_at')->get();
Eloquent #scopes in Laravel Docs
TL;DR. You can get around this by expressing your queries as MyModel::query()->find(10); instead of MyModel::find(10);.
To the best of my knowledge, starting PhpStorm 2017.2 code inspection fails for methods such as MyModel::where(), MyModel::find(), etc (check this thread), and this could get quite annoying.
One (elegant) way to get around this is to explicitly call ::query() wherever it makes sense to. This will let you benefit from free auto-completion and a nice formatting/indentating for your queries.
Examples
BAD
Snippet where inspection complains about static method calls
// static call complaint
$myModel = MyModel::find(10);
// another poorly formatted query with code inspection complaints
$myFilteredModels = MyModel::where('is_foo', true)
->where('is_bar', false)
->get();
GOOD
Well formatted code with no complaints
// no complaint
$myModel = MyModel::query()->find(10);
// a nicely formatted and indented query with no complaints
$myFilteredModels = MyModel::query()
->where('is_foo', true)
->where('is_bar', false)
->get();
Just in case this helps someone, I was getting this error because I completely missed the stated fact that the scope prefix must not be used when calling a local scope. So if you defined a local scope in your model like this:
public function scopeRecentFirst($query)
{
return $query->orderBy('updated_at', 'desc');
}
You should call it like:
$CurrentUsers = \App\Models\Users::recentFirst()->get();
Note that the prefix scope is not present in the call.
Solution to the original question
You called a non-static method statically. To make a public function static in the model, would look like this:
public static function {
}
In General:
Post::get()
In this particular instance:
Post::take(2)->get()
One thing to be careful of, when defining relationships and scope, that I had an issue with that caused a 'non-static method should not be called statically' error is when they are named the same, for example:
public function category(){
return $this->belongsTo('App\Category');
}
public function scopeCategory(){
return $query->where('category', 1);
}
When I do the following, I get the non-static error:
Event::category()->get();
The issue, is that Laravel is using my relationship method called category, rather than my category scope (scopeCategory). This can be resolved by renaming the scope or the relationship. I chose to rename the relationship:
public function cat(){
return $this->belongsTo('App\Category', 'category_id');
}
Please observe that I defined the foreign key (category_id) because otherwise Laravel would have looked for cat_id instead, and it wouldn't have found it, as I had defined it as category_id in the database.
You can give like this
public static function getAll()
{
return $posts = $this->all()->take(2)->get();
}
And when you call statically inside your controller function also..
I've literally just arrived at the answer in my case.
I'm creating a system that has implemented a create method, so I was getting this actual error because I was accessing the overridden version not the one from Eloquent.
Hope that help?
Check if you do not have declared the method getAll() in the model. That causes the controller to think that you are calling a non-static method.
For use the syntax like return Post::getAll(); you should have a magic function __callStatic in your class where handle all static calls:
public static function __callStatic($method, $parameters)
{
return (new static)->$method(...$parameters);
}
This post is a duplicate of the Github Issue here.
dart --version
Dart SDK version: 2.15.0-116.0.dev (dev) (Thu Sep 16 09:47:01 2021 -0700) on "linux_x64"
I've been looking up examples for callbacks and I have tried to get callbacks working for me in FFI.
My current situation
I have a function in my library which expects a pointer to a function. The bindings for the same generated by ffigen seem correct to me.
int SetCallback(
CallbackType callback,
) {
return _SetCallback(
callback,
);
}
late final _SetCallbackPtr =
_lookup<NativeFunction<Int32 Function(CallbackType)>>(
'SetCallback');
late final _SetCallback =
_SetCallbackPtr.asFunction<int Function(CallbackType)>();
where, typedef CallbackType = Pointer<NativeFunction<Void Function(Uint32)>>;.
What I want to do here is to setup this callback in Dart, pass it to the FFI, essentially using it as my callback as I would have in C. In my API which abstracts away from FFI code (which means I have a class MyLibrary full of static functions that the user will call directly, which in turn calls functions from an object _nativeLibrary of the class MyNativeLibrary I have created), I have:
static int SetCallback({required CallbackFuncDart callback}) {
Pointer<NativeFunction<CallbackFunc>> pointer = Pointer.fromFunction(callback);
int status = _nativeLibrary.SetCallback(
pointer,
);
if (STATUS_OK != status) {
throw LibLexemeException(status);
}
return status;
}
typedef CallbackFunc = Void Function(Uint32);
typedef CallbackFuncDart = void Function(int);
While the sqlite ffi example states here that
Features which dart:ffi does not support yet:
Callbacks from C back into Dart.
I believe the docs haven't been updated to reflect the changes at the samples here. The samples haven't been very clear due to them not having any C/C++ files, or an idea of how the C functions work. Even so, I think this example contains a segment(last code block) where a Dart function is being passed as a callback which I have replicated in my program. It is not clear to me how this will work but upon trying to compile my program I get:
ERROR: ../lib/library_lexeme.dart:180:74: Error: fromFunction expects a static function as parameter. dart:ffi only supports calling static Dart functions from native code. Closures and tear-offs are not supported because they can capture context.
ERROR: Pointer<NativeFunction<CallbackFunc>> pointer = Pointer.fromFunction(callback);
The short version is that you can't pass your callnback as an argument:
static int SetCallback({required CallbackFuncDart callback}) {
Pointer<NativeFunction<CallbackFunc>> pointer = Pointer.fromFunction(callback); // <-- this isn't considered a static function
It's quite annoying but you must use a static function defined ahead of time for your dart callbacks to be called from C.
Apparently for now only static functions can be passed via ffi. But if you have to access an instance's data and you're sure that the instance exists you can use my workaround. I use a static list to the instances. This is stupid and ugly but it works for me:
class CallbackClass {
static Int8 classCallback(int id) {
final instance = instanceList[id];
return instance.instanceCallback();
}
Int8 instanceCallback() { return instanceId; }
static List<CallbackClass> instanceList = <CallbackClass>[];
late final int instanceId;
CallbackClass {
instanceId = instanceList.length;
instanceList.insert(instanceId, this);
myFFImapping.passCallback(instanceId, Pointer.fromFunction<>(classCallback);)
}
}
I omitted the necessary c code, FFI mapping and casting to correct types for clarity, so it obviously won't compile like this.
I have a class in c++ that I'm wrapping into python with pybind11. That class has a std::function, and I'd like to control how the arguments to that function are dealt with (like return value policies). I just can't find the syntax or examples to do this...
class N {
public:
using CallbackType = std::function<void(const OtherClass*)>;
N(CallbackType callback): callback(callback) { }
CallbackType callback;
void doit() {
OtherClass * o = new OtherClass();
callback(o);
}
}
wrapped with
py::class_<OtherClass>(...standard stuff...);
py::class_<N>(m, "N")
.def(py::init<N::CallbackType>(),
py::arg("callback"));
I all works: I can do this in python:
def callback(o):
dosomethingwith(o)
k = N(callback)
, but I'd like to be able to control what happens when callback(o); is called - whether python then will take ownership of the wrapped o variable or not, basically.
I put a printout in the destructor of OtherClass, and as far as I can tell, it never gets called.
OK, I think I figured it out:
Instead of std::function, use a pybind11::function:
using CallbackType = pybind11::function
and then
void doit(const OtherClass &input) {
if (<I want to copy it>) {
callback(pybind11::cast(input, pybind11::return_value_policy::copy));
} else {
callback(pybind11::cast(input, pybind11::return_value_policy::reference));
}
}
I see nothing in pybind11/functional that allows you to change the ownership of the parameters at the point of call, as the struct func_wrapper used is function local, so can not be specialized. You could provide another wrapper yourself, but in the code you can't know whether the callback is a Python function or a bound C++ function (well, technically you can if that bound C++ function is bound by pybind11, but you can't know in general). If the function is C++, then changing Python ownership in the wrapper would be the wrong thing to do, as the temporary proxy may destroy the object even as its payload is stored by the C++ callback.
Do you have control over the implementation of class N? The reason is that by using std::shared_ptr all your ownership problems will automagically evaporate, regardless of whether the callback function is C++ or Python and whether it stores the argument or not. Would work like so, expanding on your example above:
#include <pybind11/pybind11.h>
#include <pybind11/functional.h>
namespace py = pybind11;
class OtherClass {};
class N {
public:
using CallbackType = std::function<void(const std::shared_ptr<OtherClass>&)>;
N(CallbackType callback): callback(callback) { }
CallbackType callback;
void doit() {
auto o = std::make_shared<OtherClass>();
callback(o);
}
};
PYBIND11_MODULE(example, m) {
py::class_<OtherClass, std::shared_ptr<OtherClass>>(m, "OtherClass");
py::class_<N>(m, "N")
.def(py::init<N::CallbackType>(), py::arg("callback"))
.def("doit", &N::doit);
}
I've just started making libraries in Arduino. I've made a library named inSerialCmd. I want to call a function named delegate() that is defined in the main program file, stackedcontrol.ino, after the inSerialCmd library is included.
When I try to compile, one error is thrown:
...\Arduino\libraries\inSerialCmd\inSerialCmd.cpp: In member function
'void inSerialCmd::serialListen()':
...\Arduino\libraries\inSerialCmd\inSerialCmd.cpp:32: error:
'delegate' has not been declared
After doing a bit of searching, it seemed that adding the scope resolution operator might do the trick. So I added the "::" before delegate(), now "::delegate()", but the same error is thrown.
Now I'm stumped.
You cannot and should not directly call a function in a program from a library. Keep in mind a key aspect that makes a library into a library:
A library does not depend on the specific application. A library can be fully compiled and packaged into the .a file without the existence of a program.
So there is a one way dependency, a program depends on a library. This at first glance may seem to prevent you from achieving what you want. You can achieve the functionality you are asking about through what is sometimes referred to as a callback. The main program would provide to the library at runtime a pointer to the function to execute.
// in program somwehere
int myDelegate(int a, int b);
// you set this to the library
setDelegate( myDelegate );
You see this in the arduino if you look at how interrupt handlers are installed. This same concept exists in many environments - event listeners, action adapters - all with the same goal of allowing a program to define the specific action that a library cannot know.
The library would store and call the function via the function pointer. Here is a rough sketch of what this looks like:
// in the main program
int someAction(int t1, int t2) {
return 1;
}
/* in library
this is the delegate function pointer
a function that takes two int's and returns an int */
int (*fpAction)(int, int) = 0;
/* in library
this is how an application registers its action */
void setDelegate( int (*fp)(int,int) ) {
fpAction = fp;
}
/* in libary
this is how the library can safely execute the action */
int doAction(int t1, int t2) {
int r;
if( 0 != fpAction ) {
r = (*fpAction)(t1,t2);
}
else {
// some error or default action here
r = 0;
}
return r;
}
/* in program
The main program installs its delegate, likely in setup() */
void setup () {
...
setDelegate(someAction);
...
I register my application to receive notification when the system is suspended or resumed.
MSDN documentation
Function I'd like to be executed after application receives notification (I tried both void and void CALLBACK and both work same way):
void isConnectedStandby()
{
printf( "ConnectedStandby Request");
}
1st case - I provide pointer to the isConnectedStandby function, but system treats as a double pointer to the function - it calls an address which is under this callback pointer.
HPOWERNOTIFY RegistrationHandle;
PowerRegisterSuspendResumeNotification(
DEVICE_NOTIFY_CALLBACK,
&isConnectedStandby,
&RegistrationHandle
);
2nd case - here I provide as follows (this way my function code is executed):
typedef void (*StatusFunction_t)();
StatusFunction_t StatusFunction = isConnectedStandby;
HPOWERNOTIFY RegistrationHandle;
PowerRegisterSuspendResumeNotification(
DEVICE_NOTIFY_CALLBACK,
&isConnectedStandby,
&RegistrationHandle
);
System calls not only mine function, but all addresses after the first one (if I provide an array of functions, it executes one after another to crash when there is no valid code available)
What is the correct way to use this function?
Function declaration (must be static ULONG with 3 parameters as you can see below):
static ULONG isConnectedStandby(PVOID Context, ULONG Type, PVOID Setting);
ULONG isConnectedStandby(PVOID Context, ULONG Type, PVOID Setting)
{
printf( "ConnectedStandby Request");
return 0;
}
Istead of providing callback function directly to PowerRegisterSuspendResumeNotification we have to provide struct _DEVICE_NOTIFY_SUBSCRIBE_PARAMETERS filled with our functions address :
static _DEVICE_NOTIFY_SUBSCRIBE_PARAMETERS testCallback = {
isConnectedStandby,
nullptr
};
HPOWERNOTIFY RegistrationHandle;
PowerRegisterSuspendResumeNotification(
DEVICE_NOTIFY_CALLBACK,
&testCallback,
&RegistrationHandle
);
MSDN documentation did not mention any of those information.