[syslinux] isohybrid and ISO images whose size is not a multiple of 2048 bytes vs. VirtualBox

Ady ady-sf at hotmail.com
Mon May 18 13:08:02 PDT 2015


> 
> I have meanwhile adopted in xorriso-1.4.0 the workaround of
> intrigery's team mate anonym. I.e. if the user forces a
> cylinder size that is not divisible by 2048 and the number
> of cylinders does not heal this problem, then 1536, 1024
> or 512 padding bytes get added. (Previous versions of
> xorriso did not align to cylinders but to 2048 in such a
> case.)
 
There are a couple of potential issues with that approach.

Since the size of the resulting isohybrid image would be effectively 
larger than the values in its MBR / partition table, there is a chance 
that it could have some potential problems. This is not easily seen, 
and it would only be triggered by some tool or some BIOS depending (or 
using) the mbr / partition table values (as opposed to pure LBA).

Although modern firmware does not depend on the CHS values, there are 
tools that make use of it (at least for providing information to the 
user, if not for actual actions).

The second potential issue is with the expected location of the backup 
GPT partition table, "at the end" of a GPT'ed device. This is currently 
not a problem for TAILS, but it might be for others.

I have not tested these potential situations, and I don't know whether 
they will be encountered in real-life cases. I am just commenting on 
them, so people would be aware of these potential cases.

The "correct" solution is already known, and I have already expressed 
my opinion about it.

Regards,
Ady.


More information about the Syslinux mailing list