[syslinux] uefi and bios bootable optical media

[Ady]

> We have been using syslinux (V4.05) in our product for years without a problem.
> Since we encounter more and more systems that do a UEFI boot by default
> we want to support that too. So I've been using syslinux V6.03 to create
> usb sticks and harddisks to allow both bios and uefi boot which works fine.
> 
> The problem I run into now is that it is not possible to create a
> dvd that is capable of booting in both ways. That is, I can create a
> dvd, select a bootfile from efi but the boot itself fails. On vmware
> the virtual machine powers off:
> 
> 5-02-17T11:35:21.009Z| vcpu-0| I120: Guest: About to do EFI boot: \efi\boot\bootx64.efi
> 5-02-17T11:35:21.011Z| vcpu-0| I120: Msg_Post: Error
> 5-02-17T11:35:21.011Z| vcpu-0| I120: [msg.efi.exception] The firmware encountered an unexpected exception. The virtual machine cannot boot.
> 
> If I specify another bootfile like shellx64.efi it will start, so
> the process of creating the dvd and starting images is fine, the
> issue is pure with syslinux. Bios boot from that dvd is fine fwiw.
> 
> Then I found this:
> 
>     http://www.syslinux.org/archives/2014-November/022780.html
> 
>  >For Syslinux (BIOS and EFI) in the .iso file:
>  >_ the user might assume that the system can boot from optical media
>  >not only in BIOS mode but also in UEFI mode (sadly, the latter is
>  >currently untrue);
> 
> That looks to be my problem.
> 
>  >Realistically, less and less users are using optical media,
>  >especially on newer computers (which are of course UEFI systems).
>  >This means that investing resources in Syslinux development with the
>  >specific goal of achieving bootable optical media in UEFI mode is
>  >less "productive" than investing resources to achieve other
>  >improvements / features. I'm not saying it won't happen - possibly by
>  >adding some other, more-important features, then booting optical
>  >media in UEFI mode might be also achievable.
> 
> Well, physical media are used less and less, I agree with that part.
> On the other hand, a lot of installations on servers are done with
> virtual media booting from a virtual dvd via an iso file, so it's
> still used a lot.
> 
> So what can I do about this? Switch to grub? I really hate that
> but if there's no alternative I may have to do that.
> 
> Or I may try to fix the issue myself. So is there anyone out there
> that already knows a bit about this, and what the area is with the
> pain? Or even if there's already been done some work to get it
> to work?
> 
> Thanks,
> 
> Jur van der Burg.
 
The problem is "simple": syslinux.efi v.6.03 can boot from the 
filesystems supported by SYSLINUX/EXTLINUX, and can network boot 
(similarly as PXELINUX), but currently it doesn't understand ISO9660 
(as ISOLINUX can).

About what you could do, perhaps instead of using "iso images" in 
virtual environments, you could use network booting (similarly as 
PXELINUX for BIOS systems).

About fixing the issue yourself, could you add support for ISO9660 in 
syslinux.efi? Patches are welcome!.

Regards,
Ady.

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