Hi,

How does LDC handle emitting thunks to external modules that accept variadic parameters?

If under the same object file, you can happily emit:

sub    offset, %thisreg
jmp    method

But if doing separate compilation, many targets to not support doing such operations across section boundaries.  So a more general/agnostic way to go about it is by copying all arguments, adjusting the 'this' pointer and calling target method at the codegen level.  This works so long as you are not dealing with a variadic method (ie: std.stream.Stream.printf)

Example code below:

A.d
---
module A;

interface I_A
{
    bool a(...);
}

class C_A : I_A
{
    bool a(...) { return false; }
}


B.d
---
module B;

import A;

interface I_B : I_A
{
    void b();
}

abstract class C_B : C_A, I_B
{
    abstract void b();
}

void main() { }

"Iain Buclaw via Digitalmars-d"  wrote in message news:mailman.1364.1428563414.3111.digitalmars-d@puremagic.com...

> If under the same object file, you can happily emit:
>
> sub    offset, %thisreg
> jmp    method
>
> But if doing separate compilation, many targets to not support doing
> such operations across section boundaries.  So a more general/agnostic
> way to go about it is by copying all arguments, adjusting the 'this'
> pointer and calling target method at the codegen level.  This works so
> long as you are not dealing with a variadic method (ie:
> std.stream.Stream.printf)

They don't support jumping across section boundaries?  But they do support calling?

Anyway it sounds like

sub offset, %thisreg
call method
ret

would do it 

On 9 April 2015 at 13:20, Daniel Murphy via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> "Iain Buclaw via Digitalmars-d"  wrote in message news:mailman.1364.1428563414.3111.digitalmars-d@puremagic.com...
>
>> If under the same object file, you can happily emit:
>>
>> sub    offset, %thisreg
>> jmp    method
>>
>> But if doing separate compilation, many targets to not support doing such operations across section boundaries.  So a more general/agnostic way to go about it is by copying all arguments, adjusting the 'this' pointer and calling target method at the codegen level.  This works so long as you are not dealing with a variadic method (ie: std.stream.Stream.printf)
>
>
> They don't support jumping across section boundaries?  But they do support calling?
>
> Anyway it sounds like
>
> sub offset, %thisreg
> call method
> ret
>
> would do it

That's not copying arguments. :-)

Iain.

On 9 April 2015 at 14:38, Iain Buclaw <ibuclaw@gdcproject.org> wrote:
> On 9 April 2015 at 13:20, Daniel Murphy via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
>> "Iain Buclaw via Digitalmars-d"  wrote in message news:mailman.1364.1428563414.3111.digitalmars-d@puremagic.com...
>>
>>> If under the same object file, you can happily emit:
>>>
>>> sub    offset, %thisreg
>>> jmp    method
>>>
>>> But if doing separate compilation, many targets to not support doing such operations across section boundaries.  So a more general/agnostic way to go about it is by copying all arguments, adjusting the 'this' pointer and calling target method at the codegen level.  This works so long as you are not dealing with a variadic method (ie: std.stream.Stream.printf)
>>
>>
>> They don't support jumping across section boundaries?  But they do support calling?
>>
>> Anyway it sounds like
>>
>> sub offset, %thisreg
>> call method
>> ret
>>
>> would do it
>
> That's not copying arguments. :-)
>
> Iain.

What is currently happening in GDC (Generic thunks don't support
varargs though).

https://github.com/D-Programming-GDC/GDC/pull/97#issuecomment-90275901

"Iain Buclaw via Digitalmars-d"  wrote in message news:mailman.1372.1428583102.3111.digitalmars-d@puremagic.com...

> That's not copying arguments. :-)

True, but why doesn't jump work? 

On 9 April 2015 at 15:39, Daniel Murphy via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> "Iain Buclaw via Digitalmars-d"  wrote in message news:mailman.1372.1428583102.3111.digitalmars-d@puremagic.com...
>
>> That's not copying arguments. :-)
>
>
> True, but why doesn't jump work?

Many targets do not support thunks (PPC, IA64, MIPS) - even i386 has
it's limitations (if there are no free registers, it's tilt game
over!).

>From conversations I've been having with GCC folks, jmp won't work
across shared libraries either it seems.