[Mono-dev] Embedded API: .ctor method signature query [mono]

[Robert Jordan]

Hi Jonathan,

The JIT isn't using these functions for method look-ups.

mono_method_descs are mainly for embedders (and for
trivial method look-ups at some places inside the runtime).

They come handy when you want to get an overloaded
MonoMethod in C/C++:

easy:

desc = mono_method_desc_new (":Method(int, string, int)");
method = mono_method_desc_search_in_class (desc, class);
mono_method_desc_free (desc);

versus hard:

- enum methods with mono_class_get_methods ()
- check method name
- check param count
- check param types
...


If you're generating stubs automatically and don't
have a string description of the methods up front,
the hard way involving mono_class_get_methods () might
be better and faster.

You may want to file a bug, though.

Robert


On 03.03.2016 19:28, Jonathan Mitchell wrote:
> HI Robert
>
> Thanks for that.
> I think you are right.
> I call hundreds of methods that take Obj`1<T> arguments with out issue but I see that I have had to construct a number of helper methods to deal with cases of Obj`2<T, K> which failed signature resolution.
>
> I presume that  managed code execution doesn’t involve calls to mono_method_desc_new() - are thunks used instead?
> One of the difficulties, I find, of working with the embedded API is trying to visualise just how a particular managed code statement is implemented within the runtime.
>
> I was hoping to be able to call the constructor from C with a pointer to a static (MonoString *)fund(MonoString *).
> Not sure if that would even fly.
>
> As a work around I will use an internal call.
>
> Shall I log this as a bug and reference this thread?
>
> Thanks a lot for replying.
>
> Jonathan
>
>> On 3 Mar 2016, at 18:02, Robert Jordan <robertj at gmx.net> wrote:
>>
>> On 03.03.2016 14:36, Jonathan Mitchell wrote:
>>> HI
>>>
>>> I want to call the following constructor via the embedded API:
>>>
>>> public CloudClient(Func<string, string> filePathCallback)
>>>
>>> All my other embedded method and constructor calls work okay but there is an issue with this one - it is the only place I use a System.Func<T>.
>>> The API reports that a method cannot be found for signature .ctor(System.Func`2<string, string>)
>>> When I dump out the class method names I see .ctor(System.Func`2<string, string>) listed.
>>>
>>> Any ideas on this one?
>>
>> It looks like a bug in mono_method_desc_new ():
>>
>> https://github.com/mono/mono/blob/master/mono/metadata/debug-helpers.c#L378
>>
>> The function is treating
>>
>> 	.ctor(System.Func`2<string, string>)
>>
>> like a method with 2 arguments:
>>
>> arg0 = System.Func`2<string
>> arg1 = string>
>>
>> This is obviously wrong :)
>>
>> The function is then storing the (wrong) argument count
>> for optimization purposes, and the comparison of methods
>> is starting to fail:
>>
>> https://github.com/mono/mono/blob/master/mono/metadata/debug-helpers.c#L447
>>
>> Robert
>>
>>