On Wed, 2019-02-13 at 20:57 +0100, Matthijs Kooijman wrote:
> Package: live-build
> Version: 1:20180925
> Severity: wishlist
> Hi folks,
> currently, live-build seems to only support EFI systems using the
> grub-efi bootloader, but not for netboot or hdd images (effectively
> only
> for iso images, I believe).
> Syslinux also has an EFI version, that can be installed through
> the syslinux-efi package. It would be useful for live-build to
> support
> this. I need this for a client, so I'm planning to implement support
> in
> the coming weeks. This report serves to track progress and discuss
> the implementation.
> I've done some experiments by adding syslinux-efi to an existing
> image
> manually (not with a full live-build image, but with my own hdd image
> that at least uses live-build for building the image, so should be
> representative in this area). This shows that adding syslinux-efi is
> fairly easy. The existing FAT partition can function as an ESP (EFI
> System Partition) as it is now.
> Installing the bootloader is a matter of dumping some files in the
> EFI/BOOT directory. This lets the bootloader be detected as a
> fallback
> bootloader, which is AFAIU intended for removable media. Syslinux
> needs
> some additional files (ldlinux, additional modules, configuration)
> which
> can live in that same directory.
> Both 32-bit and 64-bit EFI can be supported at the same time, by
> installing both versions of syslinux-efi (named bootx64.efi and
> bootia32.efi respectively). One caveat is that syslinux needs
> different
> .c32 modules for both architectures (though they are both named .c32
> and
> are explicitly referenced in the config file). This means either
> duplicating the bootloader configuration file for 32 and 64 bit
> (which
> hinders modifications to the config), or putting the modules in
> subdirectories and using the PATH config directive to point to either
> directive before including the common configuration. I have not tried
> this latter approach but it is described here (though currently
> syslinux.org seems to be unavailable, I tried the Google cache):
> https://www.syslinux.org/archives/2014-August/022545.html
> (subject: syslinux efi configuration file name proposal)
> I've also tried to let the syslinux-efi config file include the
> normal
> syslinux configuration file (or at least the bulk that is in
> live.cfg),
> which seems to work just fine.
> Since config sharing is easy and syslinux-efi is a matter of adding
> some
> files to the existing image, it would make sense to add syslinux-efi
> by
> default on normal syslinux hdd images (perhaps adding a new option to
> disable this?). This also seems to hold for ISO9660 images, where
> it seems isohybrid can include a small FAT filesystem with the
> bootloader files. This might need some additional work to generate
> the
> filesystem image and/or pass options when generating the iso. See:
> https://www.syslinux.org/wiki/index.php?title=Isohybrid#UEFI
> Using syslinux-efi exclusively (e.g. passing it to --bootloader and
> not
> installing normal syslinux) might also be an extra option. However,
> I'm
> not much interested in this case, so I will likely not implement it
> (I'll try not to make it too hard to add it later).
> In terms of code, this is probably best implemented in the existing
> binary_syslinux script. The bulk of what needs to happen is
> essentially
> copying bootloader files from config/bootloaders into binary, taking
> care to resolve symlinks. I'm planning to put the code that does that
> into a shell function, so it can be called at the current place and
> then
> a second time for syslinux-efi later.
> I think it would be good to copy files *from*
> config/bootloaders/syslinux-efi-addon or something similar, to leave
> config/bootloaders/syslinux-efi available for an EFI-only image.
> These
> two directories would be identical in terms of syslinux binary files,
> but the configurations would differ (the addon would include the
> normal
> boot/syslinux/syslinux.cfg, while the standalone version would
> contain
> the complete config).
> I haven't really looked at the iso version yet (which is also not my
> primary interest, but I think it would be good to handle as well).
> Happy to hear any thoughts :-)
> Gr.
> Matthijs


At a quick glance it all sounds good to me, although I can't say I have
a lot of experience with syslinux.

For feature parity, I'd encourage to look into supporting Secure Boot
like the grub-efi implementation does, since we are preparing to ship
that in Debian 10. It's not much extra work on top of adding the rest

Kind regards,
Luca Boccassi

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