Re: edk2 and gnu-efi calling schemes

[Laszlo Ersek <lersek@redhat.com>]

On 12/07/18 14:26, Knop, Ryszard wrote:
> Hi Laszlo,
> Regarding "functions that take variable arguments must be EFIAPI, even if they are STATIC (long story)" - what's the story? :)

If I remember correctly, the issue was that the VA_*() macros could not
be implemented on gcc -- or, on *all* supported gcc toolchains at the
same time, anyway -- such that they'd work in both non-EFIAPI and EFIAPI
functions. This held for both manual stack manipulation *and* gcc
builtins, in the macros -- the gcc builtins would not auto-adapt (at
compile time) to the actual calling convention of the containing function.

Therefore, the VA_*() macros had to make a one-time choice (between
being usable in EFIAPI vs. non-EFIAPI functions). Given that variable
arguments are taken by both some edk2 lib class APIs, and (more
importantly) some UEFI services (ex.
gBS->InstallMultipleProtocolInterfaces()), VA_*() were made to assume
EFIAPI in the containing function.

So, I guess, to be more precise, I should say "functions that take
variable arguments must be EFIAPI, as long as you want to use VA_*()
macros in them".

This is my recollection anyway.

Thanks
Laszlo