Re: [PATCH v2 1/2] efi: Drop __grub_efi_api attribute from shim_lock->verify() call

[Ard Biesheuvel]

On Fri, 30 Jun 2023 at 03:35, Glenn Washburn
<development@efficientek.com> wrote:
>
> On Thu, 29 Jun 2023 20:02:31 +0200
> Daniel Kiper <daniel.kiper@oracle.com> wrote:
>
> > ... because (surprisingly) it uses System V AMD64 ABI on x86-64
> > architecture...
> >
> > Fixes: 6a080b9cd (efi: Add calling convention annotation to all prototypes)
> >
> > Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
> > Acked-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> >  include/grub/efi/api.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h
> > index 16161e1f0..f3c50ed5d 100644
> > --- a/include/grub/efi/api.h
> > +++ b/include/grub/efi/api.h
> > @@ -1777,7 +1777,7 @@ typedef struct grub_efi_block_io grub_efi_block_io_t;
> >
> >  struct grub_efi_shim_lock_protocol
> >  {
> > -  grub_efi_status_t (__grub_efi_api *verify) (void *buffer, grub_uint32_t 
> > size);
> > +  grub_efi_status_t (*verify) (void *buffer, grub_uint32_t size);
>
> I would suggest adding a comment above this line, something like:
>
>   The shim_lock_protcol uses System V AMD64 ABI on x86-64 as specified
>   in __insert specification reference here__, unlike most UEFI protocol
>   methods, which use the MSABI calling convention.
>
> I may have some details wrong in the above, so change as needed. Also,
> I'm confused by your commit message. If this is only on x86-64, what
> about the other EFI architectures? This change's contents suggest it
> applies to all of them. Or is the shim lock protocol itself limited to
> x86-64 architectures?
>


Conceptually, it applies to all architectures. However, x86_64 is the
only architecture where the EFI calling convention deviates from the
Linux/SysV calling convention, which is what GRUB uses internally.

For this reason, __grub_efi_api expands to an empty string on non-x86
architectures (on 32-bit x86, it expands to regparm(0) but this should
be the default in any case)