[Bug-xorriso] Acer Aspire V5-121 doesn't see USB ISO as bootable

[Carlo Caione]

Hey Thomas,
we are having a problem with an Acer Aspire V5-121 when trying to boot
the Endless ISO from an USB device.

The iso is structured like:

xorriso : NOTE : Loading ISO image tree from LBA 0
xorriso : UPDATE : 300 nodes read in 1 seconds
libisofs: WARNING : Found hidden El-Torito image. Its size could not
be figured out, so image modify or boot image patching may lead to bad
results.
xorriso : NOTE : Detected El-Torito boot information which currently
is set to be discarded
Drive current: -indev 'eos-master-amd64-amd64.170209-111324.base.iso'
Media current: stdio file, overwriteable
Media status : is written , is appendable
Boot record  : El Torito , MBR grub2-mbr cyl-align-off
Media summary: 1 session, 1062198 data blocks, 2075m data,  107g free
Volume id    : 'Endless-OS-3-1-0-base'
El Torito catalog  : 80  1
El Torito cat path : /boot.catalog
El Torito images   :   N  Pltf  B   Emul  Ld_seg  Hdpt  Ldsiz         LBA
El Torito boot img :   1  BIOS  y   none  0x0000  0x00      4     1059972
El Torito boot img :   2  UEFI  y   none  0x0000  0x00  18432     1062198
El Torito img path :   1  /endless/grub/i386-pc/iso/eltorito.img
El Torito img opts :   1  boot-info-table grub2-boot-info
El Torito img blks :   2  4608
System area options: 0x00004a00
System area summary: MBR grub2-mbr cyl-align-off
ISO image size/512 : 4248792
Partition offset   : 0
MBR heads per cyl  : 0
MBR secs per head  : 0
MBR partition table:   N Status  Type        Start       Blocks
MBR partition      :   1   0x80  0x83            0      4248792
MBR partition      :   2   0x00  0xef      4248792        18432

and it is generated by:

xorriso -as mkisofs -o ${OUTPUT} -r -graft-points -no-pad
--sort-weight 0 --sort-weight 1 /endless --grub2-mbr
.../boot_hybrid.img -append_partition 2 0xef .../efi.img -b
.../eltorito.img -no-emul-boot -boot-load-size 4 -boot-info-table
--grub2-boot-info -eltorito-alt-boot -e
--interval:appended_partition_2:all:: -no-emul-boot -iso-level 3
${DIR_IMAGES}

In the BIOS there is no boot menu, there is only a boot priority order
in setup. There it just shows "USB HDD:" and if we put it at the top
it still boots straight into windows.
Since we also noticed that when flashing a recent Ubuntu
zesty-desktop-amd64.iso to the same USB disk the BIOS setup shows "USB
HDD: Transcend Jetflash" (and it successfully boots into Ubuntu)
probably there is something the UEFI is not happy about concerning our
ISO.
Anything you can notice / suggest that would make UEFI seeing our
image correctly? Our guess it's that the firmware is particularly
picky about something, since we can boot the image just fine on a lot
of other platforms.

Thanks,

-- 
Carlo Caione  |  +39.340.80.30.096  |  Endless