UEFI ISO boot not working in 12.1 ?

[Chris Ross]

On Thu, Nov 07, 2019 at 02:53:25PM -0500, Chris Ross wrote:
> > > On Thu, Nov 7, 2019 at 9:46 AM Julian Elischer <julian at freebsd.org> wrote:
> > >> You could try some bisection back along the  12 branch..
> 
> Yeah.  I was hoping for an easier path, but.  I can try slogging back
> through stable-12 a month or two at a time.

Okay.  I spent a bunch of time moving around stable-12 by date, and
an ISO build from stable-12 as of 2019-10-14 works (rev 353483), and
2019-10-15 (rev 353541) does not.

The svn update across that day shows:

Updating '.':
U    stand/efi/boot1/boot1.c
U    stand/efi/include/efilib.h
U    stand/efi/libefi/devpath.c
U    stand/efi/libefi/efinet.c
U    stand/efi/libefi/efipart.c
U    stand/efi/libefi/libefi.c
U    stand/efi/loader/arch/i386/efimd.c
U    stand/efi/loader/efi_main.c
U    stand/efi/loader/framebuffer.c
U    stand/efi/loader/main.c
U    stand/libsa/stand.h
U    stand/libsa/zalloc.c
U    stand/libsa/zalloc_defs.h
U    stand/libsa/zalloc_malloc.c
U    stand/libsa/zalloc_mem.h
U    stand/libsa/zalloc_protos.h
 U   .
Updated to revision 353541.

So, there's the commit/commits.  Can someone else who knows the intra-branch
process better help me determine where the original change came from,
what it was meant to accomplish, then hopefully we can find out what went
wrong for at least my hardware?

Thanks all!

                 - Chris