[Mono-devel-list] Callling convention for interop call-backs

[Karl Waclawek]

----- Original Message ----- 
From: "Liyu Liu" <liyul at hotmail.com>

> There are two issues with interop:
> 1. should winapi be cdecl or stdcall?
> 2. Can mcs be extended to support specifying call conventions in delegate as
> an extension to C#?
> 
> There are only two call conventions supported in .net, --cdecl or stdcall.
> For Microsoft implementation, winapi is stdcall on win32 and cdecl on CE.

I think anything that calls itself winapi should follow MS' example.

> The fastcall is almost never used. Currently mono on win32 take default
> winapi as cdecl which created compatibility problems. Any assembly
> containing P/Invoke working with mono, like Mono.Data.SqliteClient etc,
> cannot work with Microsoft .net runtime without source code change and
> recompilation. Also same vice versa.

Not good.
 
> Microsoft's csc doesn't have support for cdecl for callback, thus people has
> to be resorted to IL hack to change such
> 
>       .method public hidebysig virtual instance int32
>               Invoke(native int o,
>                      int32 argc,
>                      int8** argv,
>                      int8** colnames) runtime managed
>       {
>       } // end of method SqliteCallbackFunction::Invoke
> 
>    to
>       .method public hidebysig virtual instance int32
> modopt([mscorlib]System.Runtime.CompilerServices.CallConvCdecl)
>               Invoke(native int o,
>                      int32 argc,
>                      int8** argv,
>                      int8** colnames) runtime managed
>       {
>       } // end of method SqliteCallbackFunction::Invoke
> 
> This should be relatively easy to support in mcs and mono.

I would think so too.
 
> It is a breaking change. But seemed to us best way is to extend mcs to
> support cdecl callback and change mono to use stdcall as default for winapi
> on win32. This will force all P/Invoke done with mono to change to use cdecl
> explicitly. But the benefit is final assemeblies working without any hitch
> or changes across linux/win32. There will also be no need of IL hacks.

You have *my* vote.
Instead of just supporting cdecl, why not add an attribute that
allows to specify any of the calling conventions for delegates?

Karl