[edk2] edk2 and gnu-efi calling schemes

Knop, Ryszard ryszard.knop at intel.com
Fri Dec 7 05:26:16 PST 2018

Hi Laszlo,
Regarding "functions that take variable arguments must be EFIAPI, even if they are STATIC (long story)" - what's the story? :)
Thanks, Richard.

-----Original Message-----
From: edk2-devel [mailto:edk2-devel-bounces at lists.01.org] On Behalf Of Laszlo Ersek
Sent: Friday, December 7, 2018 14:07
To: Peter Wiehe <peter.wiehe2 at gmail.com>
Cc: edk2-devel at lists.01.org; Bill Paul <wpaul at windriver.com>
Subject: Re: [edk2] edk2 and gnu-efi calling schemes

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).

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