[syslinux] "isolinux.bin missing or corrupt" when booting USB flash drive in old PC

[Ady Ady]

> Hi,
> 
> Ady wrote:
> > If a specific BIOS' CHS/LBA translations cannot cope with the above, it 
> > is no surprise that we get some mess, somewhere.
> 
> Currently my suspicion is that the isohdpfx.S code simply mishandles
> the two conversion factors which it correctly got from BIOS call
> INT 13H AH 8.
> 
> 
> >  Boot  System ID   :   First    :    Last    : Relative : Number of:
> >  Flag              :Cyl Head Sec:Cyl Head Sec:  Sector  :  Sectors :
> >  80h 00h           :   0   0  1 : 646  63 32 :         0:   1325056:
> >  00h EFh ??        :1023 254 63 :1023 254 63 :      8524:       608:
> 
> The last sector 1325055 and its C/H/S (646, 63, 32) address tell that the
> partition table was made under the assumption H/C= 64 and S/H= 32.
> That's what hpa prescribed to me for smaller sized isohybrids.
> 
 
But that's my point. In theory, the geometry assumed in the MBR should 
match the one assumed by the BIOS. The isohybrid tool (or the 
equivalent code in xorriso) is using one CHS geometry, and it ends in 
its MBR (h:64;s:32).

While the image is less than 1GB, the physical device is close to 4GB, 
so the BIOS is probably assuming a different geometry. We could/should 
had had the result from the "diag/*.img" images already, as it should 
had been the first test to report.

Nowadays, most BIOS would use LBA in most cases, but that's not always 
the case, and we end up with this type of problems. Most distro 
maintainers ignore these issues, and David's case is just one 
additional example.

For an isohybrid image of ~700MB, a USB device of less than 1GB should 
be preferred.

BTW, many distros are still not setting the Head and Sector parameters 
correctly for isohybrid, so they still use "64/32" while distributing 
images of several GBs each.

I am not discarding a bug in isohybrid either. I guess a word from hpa 
or mjg could help, but I wouldn't count on that.

Regards,
Ady