[syslinux] Isohybrid wiki page and UEFI

Mon Apr 6 12:29:11 PDT 2015

On 06/04/2015 20:57, Ady via Syslinux wrote:
>
>> Hi,
>>
>> Ady wrote:
>>> This could be misinterpreted by some users as: "if
>>> you want to build an isohybrid image, then you cannot use
>>> 'syslinux.efi'". This would be incorrect.
>>
>> I don't know whether syslinux.efi can be used for booting
>> from ISO 9660 via UEFI. Currently there is no example
>> around which would succeed without GRUB or GRUB2.
>
> I don't know how many times I have to express this and in how many
> different ways: 'syslinux.efi v.6.03 cannot be used for booting from
> ISO9660 via UEFI.
>
> Can 'syslinux.efi' be included in an isohybrid image?
>   Yes, for example as 'EFI/BOOT/BOOTX64.EFI'.
>
> Can such isohybrid image be burned to optical media?
>   Yes.
>
> Can such optical media boot a BIOS system?
>   Yes, for example if 'isolinux.bin' was used as bootloader when
> building the image. Additional conditions might be required.
>
> Can such optical media boot a UEFI system in UEFI mode?
>   By means of 'syslinux.efi' v.6.03, no, it can not.
>
> Can the isohybrid image be dd'ed to a (USB flash) drive?
>   Yes. Let's call it UFD1.
>
> Can UFD1 boot a BIOS system?
>   Yes, for example if 'isolinux.bin' was used as bootloader when
> building the image. Additional conditions might be required, such as
> adequate isohybrid options.
>
> Can UFD1 boot a UEFI system in UEFI mode?
>   By means of 'syslinux.efi' v.6.03, no, it can not.
>
> Can the content of the isohybrid image be _copied_ (as opposed to
> dd'ed) to a (USB flash) drive?
>   Yes. Let's call it UFD2.
>
> If UFD2 was previously formatted with a FAT file system (before copying
> the content of the isohybrid image), can UFD2 boot a BIOS system?
>   Yes; install mbr.bin, set the "boot" flag to the FAT partition and
> install SYSLINUX to it.
>
> Can UFD2 boot a UEFI system in UEFI mode?
>   Yes. Use a GPT partition scheme (instead of the traditional MBR
> scheme) and a FAT partition. Then _copy_ (as oppose to dd'ing) the
> content of the isohybrid image to this FAT partition. Having already
> 'syslinux.efi' included in the original isohybrid image (as
> 'EFI/BOOT/BOOTX64.EFI' for UEFI x86_64 firmware) means that a FAT
> partition in a GPT drive can be used as "ESP", with 'syslinux.efi' as
> default UEFI bootloader of this device for UEFI x86_64 systems.
>
> Can the same UFD2 boot either a UEFI system or a BIOS one?
>   Yes, using 'gptmbr.bin' and combining both methods of installation for
> Syslinux.
>
> Are every-and-all (U)EFI systems bootable by a UEFI bootloader located
> in any "ESP"?
>   No. There are general recommendations, based on experience. But there
> are also buggy firmware, non-standard firmware, intentional
> customizations...
>
> Is _any_ FAT volume a valid "ESP" in any-and-every case / hardware?
>   No. There are some exceptions (intentional or not), but in time they
> should be fewer and fewer.
>
> Are there filesystems other than FAT that can be "ESP"?
>   According to the UEFI specs, yes. In practice and as a general rule,
> this possibility should not be blindly trusted.
>
> Are there systems in which a FAT volume is not accepted as "ESP"?
>   Yes, but in time they should be fewer and fewer. Please don't ask here
> for more info about such systems.
>
> Are there any additional conditions necessary to succeed in any of the
> above scenarios?
>   Yes. These are _not_ detailed step-by-step "HowTos", and I currently
> have no intention to write them either. The Syslinux wiki has more than
> 100 pages; among others:
>   http://www.syslinux.org/wiki/index.php/Install
>
> Are the ISO image building tools (e.g. mksiofs, genisoimage,
> xorriso...) related to so-called "efiboot.img" files?
>   Yes, in a similar way that they are related to any "El Torito" image.
>
> Is the isohybrid tool (in any of its variants) related to so-called
> "efiboot.img" files?
>   Yes, in a similar way that the isohybrid tool is related to any "El
> Torito" image.
>
> Is the isohybrid tool responsible of generating / building /
> constructing / filling the content of an "efiboot.img" image?
>   No.
>
> How a user creates an "efiboot.img" image file?
>   The user should consult the documentation of the respective
> bootloader. Syslinux, as of v.6.03, has nothing to do with any
> so-called "efiboot.img".
>
> Once an "efiboot.img" is created, how is it used?
>   The user should consult the documentation of the specific ISO-building
> tool in use, just as the same documentation is needed for any "El
> Torito" boot image.
>
> Is "efiboot.img" used / needed by every UEFI bootloader?
>   No. There are certain bootloaders for certain OSes that are capable of
> booting optical media in UEFI mode and are not using so-called
> "efiboot.img" files. There are also UEFI bootloaders that are _not_
> capable of booting ISO9660 file systems in UEFI mode, with or without
> so-called "efiboot.img" (it doesn't help); 'syslinux.efi' v.6.03 is one
> of the latter.
>
>
> So, again, is there any use for 'syslinux.efi' v.6.03 in an isohybrid
> image?
>   Yes.
>
> Can 'syslinux.efi' v.6.03 boot some media formatted with ISO9660?
>   Not at this time, no.
>
> If a user has an isohybrid image and pretends to boot a UEFI system in
> UEFI mode with 'syslinux.efi' v.6.03, is dd'ing this isohybrid image on
> a (USB) drive a useful method?
>   No.
>
> Hmm, but dd'ing isohybrid images is so simple...!
>   You have the freedom to waste your time.
>
> Are there any kind of images that can be dd'ed to a (USB) drive and
> that the resulting drive will be capable of using 'syslinux.efi' to
> boot a UEFI x86_64 system in UEFI mode?
>   Images of a FAT volume in a GPT partitioning scheme already containing
> 'syslinux.efi' as 'EFI/BOOT/BOOTX64.EFI' (and related files).
>
> Should users attempt to build so-called "efiboot.img" files with
> 'syslinux.efi' v.6.03 in it for ISO(hybrid) images?
>   No, there is no use; 'syslinux.efi' v.6.03 doesn't know what to do
> with it.
>
> What about users putting 'syslinux.efi' v.6.03 inside the "efiboot.img"
> file?
>   They are free to waste their time.
>
> And if users rename 'syslinux.efi' v.6.03 to '/EFI/BOOT/BOOTX64.EFI"
> inside the "efiboot.img", can it be used?
>   It only occupies space; nothing very useful.
>
>
>>
>> When describing the UEFI aspects of isohybrid in the wiki,
>> i left this question open in the hope that somebody would
>> show a pure SYSLINUX example of UEFI isohybrid.
>>
>> The questions of piranna were not the first time that we
>> had to explain our non-knowledge around ISOLINUX and UEFI.
>> The wiki needs clarification.
>
>
> For UEFI mode, there is 'syslinux.efi'. As of v.6.03, there are
> variants of 'syslinux.efi' for UEFI IA32 and for UEFI x86_64.
>
> As of v.6.03, there is no such thing as ISOLINUX for UEFI mode.
>
> If there are users asking whether there are other things for UEFI in
> The Syslinux Project as of version 6.03, the answer is: no.
>
> As of version 6.03, there is no "memdisk" for UEFI, and many popular
> c32 modules are currently for BIOS / CSM only, not UEFI.
>
> As of version 6.03, 'syslinux.efi' doesn't know yet how to chainload to
> other EFI binaries.
>
> Oh, and before I forget, if there is someone out there asking whether
> there is "chicken", "beef", or "veggies" for UEFI in The Syslinux
> Project, the answer is no :).

Hi

Just including these statements (Q & A) as is in the Syslinux wiki would 
help a lot newbies like me.

That's exactly the kind of information I'd expect to find in a FAQ.

Not all users follow this list or able to remember of find what was said 
in it time ago.

Thanks and best regards,

Diider