[cfe-dev] Re-using 'dllexport' for non-Windows targets

[Martin J. O'Riordan via cfe-dev]

Yes it is similar to, though not identical to GOT.  Also because we have a non-gas compliant assembler, there is no way of passing GOT information on to the ELF emission.  Our compiler does not have an LLVM integrated assembler unfortunately - I'm not even sure I can build an integrated assembler for VLIW with LLVM.

Thanks,

	MartinO

-----Original Message-----
From: Rafael Espíndola [mailto:rafael.espindola at gmail.com] 
Sent: 31 May 2016 16:44
To: Martin J. O'Riordan <martin.oriordan at movidius.com>
Cc: Saleem Abdulrasool <compnerd at compnerd.org>; Clang Dev <cfe-dev at lists.llvm.org>
Subject: Re: [cfe-dev] Re-using 'dllexport' for non-Windows targets

> What I do with the attribute at code-generation is mostly treat it as 
> an ordinary symbol, but I supplement their definitions with a set of 
> data structures that when linked creates an IAT or Indirect Address 
> Table that can be inspected at run-time.  This is useful because the 
> code running on the SHAVE cores is usually managed by an executive 
> running on the Sparc Leon cores, and the dynamic lookup makes the programming model a lot simpler.
> The additional semantic checks and constraints that CLang places on 
> ‘dllexport’ are also very valuable, as they make many incompatible or 
> ill-advised use-cases become compile-time errors and warnings.
>
>
>
> In summary, the CLang front-end semantics are very appropriate to my 
> requirements, and my LLVM back-end emits normal symbols, but 
> supplemented with the auxiliary IAT data structures.
>
>
>
> It would be neat if I could “borrow” the existing ‘dllexport’ 
> implementation for the most part, but in a structured well defined 
> manner.  I have had this working since LLVM v3.3, but each time I 
> update to a new version I have to rework my adaptations, and going 
> forward it would be good to have this better integrated using CLang 
> best-practices rather than the ad-hoc I have used to date.
>

OK, so the difference is just in clang?

An ELF symbol with default visibility is preemptable already. The IAT you describe sounds a lot like the got that is used for preemption in other architectures.

Cheers,
Rafael