Re: [RFC PATCH 0/3] efi/x86: add support for generic EFI mixed mode boot

[Arvind Sankar <nivedita@alum.mit.edu>]

On Thu, Feb 13, 2020 at 05:55:44PM +0000, Ard Biesheuvel wrote:
> On Thu, 13 Feb 2020 at 18:53, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > As an alternative to the new section, how about having a CONFIG option
> > to emit the 64-bit kernel with a 32-bit PE header instead, which would
> > point to efi32_pe_entry? In that case it could be directly loaded by
> > existing firmware already. You could even have a tool that can mangle an
> > existing bzImage's header from 64-bit to 32-bit, say using the newly
> > added kernel_info structure to record the existence and location of
> > efi32_pe_entry.
> >
> 
> That wouldn't work with, say, signed distro kernels.

No, the idea would be that the distro would distribute two signed
images, one 32-bit and one 64-bit, which are identical except for the
header. At install time, the installer chooses based on the system's
firmware bit-ness.

> 
> > Also, the PE header can live anywhere inside the image, right? Is there
> > any reason to struggle to shoehorn it into the "boot sector"?
> 
> It cannot. It must live outside a region described by the section headers.

It could still be inserted after .setup, or at the very end of the file, no?