[LLVMdev] ARM ATPCS ABI support

[Damjan Marion]

On Jun 24, 2011, at 12:52 PM, Alasdair Grant wrote:

>> Both NetBSD and FreeBSD seems to use older ATPCS ABI standard.
>> As I can see it is not supported in LLVM.
>> 
>> Seems that ATPCS is predecessor of AAPCS so I wonder how easy is
>> to implement it in LLVM/Clang...
>> 
>> Is it worth efforts? Any thoughts?
> 
> See http://gcc.gnu.org/ml/gcc/2010-05/msg00468.html :
> 
>  "Do they still want their OS to work on modern CPUs with any
>   degree of efficiency?  The current ABI diverged from the old for
>   good technical reasons, not just for the sake of being different."
> 
> If you want it to run efficiently on modern multicore systems you
> really need 64-bit alignment of 64-bit types.  ARM dropped support
> for the old ABI in the reference tools years ago.

Yes, long term goal is definitely to go to aapcs.

My question is more about bridging the gap until that is done 
and also providing compatibility with older binaries.

Problem is that today Clang compiles FreeBSD code as apcs-gnu
which is in my understanding wrong.

Also clang fails to compile some C++ code as SizeType is defined 
as UnsignedLong for apcs-gnu (should be UnsignedInt).