Syslinux - Aug 2015 - Chainload El Torito grub2 from syslinux from a partition table

Hello,

I have the following scenario:

- GPT Partitioned USB disk with syslinux (or extlinux) on the first 
partition and a menu to boot each partition; all of them are iso9660 
images of different linux distros,
- Before dumping every iso image into its partition space on the USB 
disk I need to remaster it changing something on its initrd to be able 
to coexist with other linux distros on the same USB drive,
- After that, I build a new remastered iso9660 file with mkisofs or xorriso,
- If I use xorriso, I select isohdppx.bin as the MBR file. If I use 
mkisofs I need to postprocess the image with isohybrid --partok.

The menu entry on syslinux.cfg for each partition is as simple as:

Konsole output
LABEL ZeroShell
MENU LABEL ^ZeroShell
COM32 boot/syslinux/c32/chain.c32
APPEND guid:xxxxx 5

So, I'm chainloading the boot sector of an hybrid iso image dumped to a 
partition.

Everything works as expected with all distros which were built to boot 
with isolinux. It works because of the isohdppx.bin MBR (or the --partok 
switch of isohybrid).

If the distro uses grub2 it fails because the "hybrid" grub2 images 
lacks the support of booting from a partition table (right?), i.e. the 
file boot_hybrid.img from grub2 *seems* not supporting booting from a 
partition table. It hangs on "Booting".

There is a way to patch this behavior allowing chainloading a grub2 
hybrid boot sector from a partition table using ext/syslinux? or the 
solution can't be a syslinux patch and must be a new version of 
boot_hybrid.img from grub2 developers?

Thanks in advance,
Emilio.

On 08/29/2015 09:14 AM, Emilio Lazo Zaia via Syslinux
wrote:
> 
> If the distro uses grub2 it fails because the "hybrid" grub2
images
> lacks the support of booting from a partition table (right?), i.e. the
> file boot_hybrid.img from grub2 *seems* not supporting booting from a
> partition table. It hangs on "Booting".
> 
> There is a way to patch this behavior allowing chainloading a grub2
> hybrid boot sector from a partition table using ext/syslinux? or the
> solution can't be a syslinux patch and must be a new version of
> boot_hybrid.img from grub2 developers?
> 
I doubt this is something that can be done in Syslinux.  Grub2 would
have to be appropriately adjusted to either be able to accept the
partition handover information from the Syslinux chainloader, or be able
to know independently which partition it is loaded from.

	-hpa