[Bug-xorriso] Re: EFI boot option in mkisofs emulation of xorriso

[KESHAV P.R.]

On Sat, Aug 14, 2010 at 20:41, Thomas Schmitt <address@hidden> wrote:
> Hi,
>
>> The ISO works perfectly. I used
>> http://www.archlinux.org/packages/community/x86_64/libisoburn/.
>
> Newest releases, as always with Arch. :)
>
>> http://bugs.archlinux.org/task/20419?getfile=5598
>> ## Usaully used xorriso command style
>
> There is a typo in "Usaully".

Typo corrected locally (in my system).

>
> Actually both are mkisofs styles. Plus --efi-boot
> as xorriso specific extension.
> xorriso has its own option set. But with the
> special task of composing bootable single-session
> images, people prefer the options which they
> know from mkisofs.
> For multi-session incremental backup one would
> not get happy with mkisofs options, though.
>
>> -eltorito-alt-boot --efi-boot efi/boot/grub2_efi.bin -no-emul-boot
>
> The options -eltorito-alt-boot and -no-emul-boot
> are already implied in --efi-boot.
> So you may just omit them.
>
> I will implement -e which would need at least
> -eltorito-alt-boot as separator from the options
> of the BIOS boot image.
>

I always prefer the exaggerated form as I can understand what
parameter is being used. I get confused with -v and -V and all the
single alphabet options.

>> http://bugs.archlinux.org/task/20419
>> "The simple (iso-root)/efi/boot/ will work for
>>  newer UEFI firmwares (those that contain ISO9660
>>  FS driver. The older firmwares need a FAT12 floppy
>> image within the iso with a el-torito boot entry
>> of Platform id 0xEF apart from the BIOS boot entry
>> (Platform ID 0x00).
>
> Interesting. I did not know that there is a EFI
> boot facility which does not use the El Torito
> Boot record on CD/DVD/Blu-ray media.
>

I need to clarify this. Actually the firmware will not launch grub2
automatically. But having this kind of setup enables me to launch
(iso-root)/efi/boot/bootx64.efi using the EFI shell (one of the best
features of UEFI) even if the el-torito boot fails. I installed my Win
7 x64 and Fedora 12 x86_64 (I do not use Fedora anymore) in this way
only.

>
> If you apply the isohybrid program then the
> emerging MBR will not know about EFI, afaik.
> Don't the older firmwares need help by the MBR
> to find the FAT12 floppy file on an USB stick ?
>

The FAT12 floppy image file is used only in case of CD/DVD boot
(eltorito only). For USB pendrives etc. it is similar to HDD. If you
read the info from uefi spec correctly in case of CD, if the firmware
detects a 0xEF el-torito entry (it can also be the only entry if you
do not want bios booting), it assumes that image is using a FATXX FS
and mounts it (like assigning a /dev/sd*). This mountpoint is
temporary. For USB uefi directly accesses it like
(usb-root)/efi/boot/bootx64.efi (or bootx86.efi etc.). Also even in
case of cd/dvd,the file is not restricted to FAT12 or to 1.44MB floppy
size. One can use even a 100MB FAT32 image in the el-torito entry and
efi will still detect it correctly.

I tried dd copy of the isohybrid image to a 4 GB pendrive, but my efi
did not detect it. I then simply extracted the iso contents to the
root of the USB (formatted as FAT32). The firmware booted this
pendrive correctly. UEFI firmware does not bother about any bootcode
in the MBR (only the partition table). Since efi has support for FS
drivers it reads the partition table, the filesystem and launches the
.efi app you specify or according to its arch naming convention.
Mostly firmwares based on EDK2
http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=Welcome_to_TianoCore
have direct iso9660 fs support.

> If i remember right, then the GRUB2 grub-mkrescue
> script constructs an ISO image with additional
> MBR that can boot from CD/DVD or from USB stick,
> both PC-BIOS and EFI.
> I have no EFI bootable hardware. So i could only
> test BIOS with CD and USB stick. It boots up to
> a grub prompt. (The user of grub-mkrescue has to
> provide the operating system files.)
>

I did not use grub-mkrescue. I used the following shell script
http://gist.github.com/410877 ,
http://aur.archlinux.org/packages.php?ID=38369 and
http://aur.archlinux.org/packages.php?ID=39601 for creating the efi
files and then the archboot_efi_img.sh script to setup the final iso.

>
>> thanks for xorriso and your help.
>
> Don't hesitate to ask for support or new
> features.
>
>
> Have a nice day :)
>
> Thomas
>
>

If you make any changes to --efi-boot option, please tell me. To try
uefi booting you can use OVMF in qemu
https://sourceforge.net/apps/mediawiki/tianocore/index.php?title=OVMF_FAQ
or EFI option in Virtualbox (exists even in OSE edition) or if you
have windows system try http://tiano-efi-duet-folder-sk.4shared.com/
EFI_DUET.exe .

Regards.

Keshav