[ipxe-devel] elilo patch for iPXE download protocol

[Michael Brown]

On Tuesday 16 Aug 2011 22:03:07 Jarrod Johnson wrote:
> I have patched elilo to use IPXE exported capabilities to download
> kernel/initrd/config.  It probably only builds on linux/gcc/x86_64
> combination due to the hackish way I coped with the calling convention
> situation.  I'm hoping some UEFI guru will enlighten me on the correct way.
>  In short, elilo code seems to have a 'uefi_call_wrapper' to swap the
> registers around to make calls *to* uefi, but does not have a provision for
> calls from UEFI to itself.  This means it expected DI, RSI, RDX, RCX, R8,
> R9 to be the arguments instead of RCX, RDX, R8, R9.  I'm presuming there is
> GCC magic to be had that I don't understand right now.

__attribute__((ms_abi)) is the relevant magic.  iPXE uses

  #if __x86_64__
  #define EFIAPI __attribute__((ms_abi))
  #endif

  #if __i386__
  #define EFIAPI __attribute__((cdecl,regparm(0)))
  #endif

to make everything work with the stock EFI headers.  All EFI headers mark 
functions with EFIAPI, so you can just call them without a wrapper:

  efirc = bs->LocateProtocol ( &guid, NULL, protocol ) );

and you can define callback functions (again, without any wrapper) as

  static EFI_STATUS EFIAPI callback ( EFI_HANDLE handle, ... ) {
    ...
  }

> This is the analogous capability for elilo. It comes in two halves. iPXE
> needed to have capabilities exposed in a UEFI protocol in much the same way
> it exports it in 'legacy boot'.  Those patches to ipxe are:
> https://git.ipxe.org/people/jbjohnso/ipxe.git/commit/d748ebf72206dcde1379b0
> 63fd9b533f7572caa5
>  https://git.ipxe.org/people/jbjohnso/ipxe.git/commit/e7b41890bc67350a9f5bc
> f7291ec859fa2174e26
>  https://git.ipxe.org/people/jbjohnso/ipxe.git/commit/45a51f99fd51b231a388b
> 1db00dfc4b18a5e9e4f
>  https://git.ipxe.org/people/jbjohnso/ipxe.git/commit/23aea6c209965546c3956
> 9a770823eabf1358a71
> 
> Apply those and 'make bin-x86_64-efi/snponly.efi and you have something
>  much like undionly.kkpxe, but for UEFI.

Will take a look at those patches as soon as I get a chance, which might not 
be for a couple of weeks.  Please poke me if I forget!

Michael