[syslinux] Sysinux 6 will not boot ISOs on BIOS (i.e. pre-UEFI) systems

Gerardo Exequiel Pozzi vmlinuz386 at yahoo.com.ar
Mon Nov 25 09:55:36 PST 2013

On 11/25/2013 08:40 AM, Thomas Schmitt wrote:
> Hi,
> Ady wrote:
>> I guess that being isolinux.bin 4.07 smaller than 32KiB (24KiB), 
>> while isolinux.bin 6.02 being bigger (42KiB), and with the addition 
>> of multiple alternative boot images in the same ISO, the chances of 
>> isolinux.bin being located on a higher sector in the media seem to be 
>> higher.
>> So, perhaps the potential problem was always there, just that the 
>> chances of actually triggering it were much lower?
> If i get Gerardo right, then he can trigger it on 6.02 without
> isohybrid and EFI just by the start address of the boot image.
> The image size does not change by this.
> Further he reports that high addresses do not harm success with
> 4.07.

Exactly, as I described previously, the simple steps to make a broken
iso image on my system. Just an ISO with two files isolinux.bin and a
"garbage" file just to force isolinux.bin go to a high LBA address. (
three files counting boot.cat). No isohybrid-mbr, no eltorito-alt-boot
for EFI.

Looks like there is something beyond LBA 65535 (As Mattias confirmed)
with isolinux.bin from 6.02.


mkdir -p /tmp/test/isolinux
cp ~/isolinux-6.02.bin /tmp/test/isolinux/isolinux.bin

## Push isolinux.bin at LBA 65570 (0x00010022)
truncate -s 128M /tmp/test/coco

## Push isolinux.bin at LBA 65058 (0x0000fe22)
# truncate -s 127M /tmp/test/coco

xorriso -as mkisofs \
        -eltorito-boot isolinux/isolinux.bin \
        -eltorito-catalog isolinux/boot.cat \
        -no-emul-boot -boot-load-size 4 -boot-info-table \
        --sort-weight -1 isolinux/isolinux.bin \
        --sort-weight +1 coco \
        -output /tmp/test.iso \
dumpet -i /tmp/test.iso
cdrecord -v -dev=5,0,0 -dao /tmp/test.iso

I can push isolinux.bin (4.07) to a really high LBA address and boot
without any issue. (Load LBA: 2048034 (0x001f4022)) ~4G

> On my own test system, a high address (263921) and 6.02 work fine.
> So we have some ingredient in the boot firmware, and some other
> in a difference between SYSLINUX 6.01 and 4.07.
> The reported symptoms differ slightly:
> Carl Duff:
>>> ISOLINUX 6.02 ETCDisolinux: Disk error 01, AX = 4279, drive FE
> Gerardo Exequiel Pozzi:
>>> When trying to boot the bad iso, I can see the isolinux welcome message
>>> but not complete "ISOLINUX 6.02 ETCD", then reboot inmediatelly.
> Have a nice day :)

PS: You are welcome Thomas (was: Thank you, too, for flying xorriso) hehe ;)

> Thomas

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Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1

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