[edk2] edk2 and gnu-efi calling schemes

Bill Paul wpaul at windriver.com
Thu Dec 6 14:46:51 PST 2018

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.


> Kind regards
> Peter Wiehe
> _______________________________________________
> edk2-devel mailing list
> edk2-devel at lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel
-Bill Paul            (510) 749-2329 | Senior Member of Technical Staff,
                 wpaul at windriver.com | Master of Unix-Fu - Wind River Systems
   "I put a dollar in a change machine. Nothing changed." - George Carlin

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