Re: edk2 and gnu-efi calling schemes

[Laszlo Ersek <lersek@redhat.com>]

On 12/06/18 23:46, Bill Paul wrote:
> Of all the gin joints in all the towns in all the world, Peter Wiehe had to 
> walk into mine at 14:34 on Thursday 06 December 2018 and say:
> 
>> OK, another question:
>>
>> when writing an UEFI application, edk2 and gnu-efi have different 64bit
>> calling schemes. Does that only apply to calling the
>> runtime-library/object file (and inside of the UEFI-application, of
>> course)? Or does the call from application to UEFI differ in both
>> toolkits, too? (If it is the latter, it would mean that the UEFI
>> standard is unprecise!)
> 
> Both the EDK and GNU EFI obey the same standards when calling UEFI APIs. Their 
> exact implementations may differ depending on the circumstances. For example, 
> GNU EFI may use the __attribute__((ms_abi)) tag to tell the compiler what ABI 
> to use, or if the compiler doesn't support this it can fall back to using some 
> compatibility wrapper macros (see lib/x86_64/efi_stub.S). Either way, you end 
> up with the same behavior.
> 
> Within a given FOO.EFI application, the application code itself can get away 
> with using whatever calling convention it wants, right up until it needs to 
> call a UEFI firmware routine. At that point, it has to follow the conventions 
> spelled out in the UEFI spec.

I'd like to add:

- in edk2, functions declared in lib class headers have to be EFIAPI;

- functions that take variable arguments must be EFIAPI, even if they
  are STATIC (long story).

Thanks
Laszlo