[PATCH 0/7] efi: Various tidy-ups and drop the default

Mon Jun 28 19:27:44 CEST 2021

On Mon, Jun 28, 2021 at 10:26:35AM -0600, Simon Glass wrote:
> Hi Heinrich,
> 
> On Mon, 28 Jun 2021 at 09:20, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >
> > On 6/28/21 4:18 PM, Simon Glass wrote:
> > > Hi Tom, Mark,
> > >
> > > On Mon, 28 Jun 2021 at 07:37, Tom Rini <trini at konsulko.com> wrote:
> > >>
> > >> On Mon, Jun 28, 2021 at 10:38:50AM +0200, Mark Kettenis wrote:
> > >>>> From: Simon Glass <sjg at chromium.org>
> > >>>> Date: Sun, 27 Jun 2021 19:48:34 -0600
> > >>>>
> > >>>> It has come to light that EFI_LOADER adds an extraordinary amount of
> > >>>> code to U-Boot. For example, with nokia_rx51 the size delta is about
> > >>>> 90KB. About 170 boards explicitly disable the option, but is is clear
> > >>>> that many more could, thus saving image size and boot time.
> > >>>
> > >>> EFI_LOADER used to be a lot smaller.  It is great to see that over the
> > >>> years UEFI support has become more complete, but a lot of that new
> > >>> code implements features that are not at all essential for just
> > >>> booting an OS from storage.  If that growth leads to the suggestion to
> > >>> disable EFI_LOADER completely by default, we're putting the cart
> > >>> before the horse.
> > >>
> > >> Well, I see I forgot to prefix my patch with RFC, but I hadn't found
> > >> EFI_LOADER being used in the wild on armv7, but wasn't sure about the
> > >> BSD families.  I did see that Debian doesn't use it, and that Armbian
> > >> doesn't even use it on aarch64.
> > >>
> > >>>> The current situation is affecting U-Boot's image as a svelt bootloader.
> > >>>
> > >>> Really?  I know UEFI has a bad reputation in the Open Source world,
> > >>> and some of its Microsoft-isms are really annoying (yay UCS-2).  But
> > >>> it works, it provides a standardized approach across several platforms
> > >>> (ARMv7, AMRv8, RISC-V) and the industry seems to like it.  Personally
> > >>> I'd wish the industry had standardized on Open Firmware instead, but
> > >>> that ship sailed a long time ago...
> > >>>
> > >>> I find it hard to imagine that 90k is a serious amount of storage for
> > >>> something that is going to include a multi-MB Linux kernel.  This
> > >>> isn't code that lives in SPL or TPL where severe size restrictions
> > >>> apply.
> > >>
> > >> In one of those cases where I need to pop back in to the other (Nokia
> > >> N900 specific) thread and see if the big size reduction really was just
> > >> disabling EFI_LOADER, it's perhaps just one of those "fun" things about
> > >> Kconfig and anything other than "make oldconfig" for spotting new config
> > >> options that default to enabled.
> > >
> > > Yes it will be interesting to see what you find there. My results on
> > > nokia_rx51 were something like this:
> > >
> > > default
> > >         arm: (for 1/1 boards) all +129370.0 bss +1136.0 data +7399.0
> > > rodata +10989.0 text +109846.0
> > >
> > > without ebbr
> > >        arm: (for 1/1 boards) all +38460.0 bss +1040.0 data +2375.0
> > > rodata +5333.0 text +29712.0
> > >
> > > with various other things:
> > > CONFIG_OF_LIBFDT_ASSUME_MASK=7
> > > # CONFIG_OF_TRANSLATE is not set
> > > # CONFIG_SIMPLE_BUS is not set
> > > # CONFIG_TI_SYSC is not set
> > > # CONFIG_CMD_FDT is not set
> > >
> > >        arm: (for 1/1 boards) all +19170.0 bss -16.0 data +360.0 rodata
> > > +3274.0 text +15552.0
> > >
> > > (Mark, in the same email:)
> > >>> FIT simply isn't fit for purpose (pun intended).  It only really works
> > >>> for booting Linux, and forces people to combine u-boot, kernel,
> > >>> initial ramdisk and other firmware components into a single image.
> > >>> That is really undesirable as:
> > >>> - This makes it sigificantly harder to update individual components of
> > >>>   such an image.  Making it hard to update a kernel is obviously a
> > >>>   serious security risk.
> > >>> - This makes it impossible to build an OS install image that works om
> > >>>   multiple boards/SoCs.
> > >
> > >
> > > I would really like to understand this better. The whole thing is a
> > > complete mystery to me.
> > >
> > > Firstly I have sometimes fiddled with booting other OSes using FIT. It
> > > seemed OK. I can't see why it only works with Linux.
> > >
> > > Secondly, I don't expect that U-Boot itself would be in the FIT.
> > >
> > > Thirdly, do you really want the kernel and initrd to be separate? At
> > > least in the systems I have used, they are built together, even having
> > > the same name, e.g.:
> > >
> > > initrd.img-5.10.40-1rodete1-amd64
> > > System.map-5.10.40-1rodete1-amd64
> > > vmlinuz-5.10.28-1rodete2-amd64
> >
> > I have not hit any distro that builds FIT images. All install vmlinux
> > and initrd as separate files.
> >
> > Why would you want to change that?
> 
> Well there is no point in having two files if one will do. Also it
> allows for a hash / signature check.

The question of "how great would it be and how many problems would it
have solved if FIT images had become popular" is one for another time.
It will always have its use cases and users but never the broad adoption
many of us felt it should have.  Bringing it up in this context won't
change that.

I'm saying this because I think there are some important technical
questions within U-Boot to resolve because the EFI loader part of U-Boot
is critical to our long term future.  And DM is an important part of our
internal design and we're (probably later than I should have) pulling
out the parts that haven't been updated so that we can deliver on some
of the overall promise of DM better, too.

-- 
Tom
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