Re: RFC: default CONFIG_EFI_STUB=y

From: James Bottomley
Date: Tue Aug 13 2013 - 14:43:38 EST

On Tue, 2013-08-13 at 11:30 -0700, H. Peter Anvin wrote:
> On 08/09/2013 08:38 AM, H. Peter Anvin wrote:
> > On 08/09/2013 08:32 AM, James Bottomley wrote:
> >> On Fri, 2013-08-09 at 08:23 -0700, H. Peter Anvin wrote:
> >>> I would like to change the defaults for CONFIG_EFI and CONFIG_EFI_STUB
> >>> to y. There is little reason to omit this since EFI now is a
> >>> significant percentage of all systems.
> >>
> >> You didn't actually attach the patch, but I presume this is for 64 bit
> >> compiles on x86 only? We still have significant problems getting 64 bit
> >> EFI to interact with 32 bit kernels, so I don't believe we should enable
> >> CONFIG_EFI globally for all of x86.
> >>
> >
> > Well, it doesn't *solve* the problem with cross-mode, but it should work
> > as-is for EFI32->32-bit kernel and EFI64->64-bit kernel. For the
> > cross-mode kernels they will simply not do anything.
> >
> > Either way, nothing bad should come from it. The worst thing that will
> > happen is that the kernel says "I don't have any EFI that I recognize."
> >
> > Cross-mode support will always require a secondary bootloader (since as
> > far as I know there is no concept of "fat binaries" for EFI), but Matt
> > Fleming is working on genuine cross-mode support for both the boot stub
> > and (eventually) run time support.
> >
> James, does this address your concerns?

You mean for globally enabling CONFIG_EFI on x86? not really for 32
bit, you say above it's pretty much unusable; I'd prefer just to enable
it for 64 bit. As you said in your original post "since EFI now is a
significant percentage of all systems" but you actually mean EFI64 ...
EFI32 is a pretty insignificant percentage of all systems.

Can we actually boot a 32 bit kernel on an EFI64 system? The last time
I tried on my Secure Boot SDV it wouldn't work; the problem is getting
someting in the transfer of control path to boot the processor back to
32 bit mode.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at