Fragile ABI

[Michel Fortin]

On 2012-08-17 14:13:10 +0000, "R Grocott" <rgrocottbugzilla at gmail.com> said:

> On Friday, 17 August 2012 at 13:42:27 UTC, Michel Fortin wrote:
>> It's certainly doable if you put it at the right place. But druntime is 
>> not the one in charge of dynamic linking: the dynamic linker from the 
>> OS is, so that's the ideal place to do such a thing. If you want to do 
>> it in druntime it'll be a huge hassle, if doable at all it'll probably 
>> break easily. But on the OS side you hit a rock because of different 
>> approach to dynamic linking (Windows does not really have a dynamic 
>> linker).
> 
> So basically, any system to create a more sensible ABI needs to built 
> on top of the C ABI, name mangling, editable vtables, and nothing else? 
> Ouch.

That's pretty much it yes.

> If druntime can't detect whether symbols were dynamically or statically 
> linked, does that mean that your system would add an overhead to *all* 
> virtual function calls, not just those which call into a dynamic 
> library?

Yes. Neither druntime nor the compiler knows whether you're creating an 
executable. The typical compilation process is to convert D code to an 
object file containing machine code. Then that object file is linked 
either inside an executable or inside a shared library. But the machine 
code is written before the compiler knows where it'll go.

> If so, that'd be a pretty strong argument against implementing anything 
> like it, unless it's something which has to be explicitly switched on 
> (using, say, an "extern(D_FlexibleABI)" statement).

Exactly my thoughts.

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca/