Syslinux - Dec 2019 - chainloading syslinux problem

Hi!
I have bootable (USB flash) disk, that _appears_ to be using syslinux.
(the word syslinux is in the PBR, in the hexdump).
How can I chainload it? The payload seems to be a file that I tried
load with COMBOOT, COM32 etc, but nothing works (they report that the
file is not in proper format, wrong magic number or simply crash). How
to proceed?

is there a 100% way to confirm that it is really syslinux? So I don't
waste your time if it isnt

Regards,
David

On Tue, 2019-12-17 at 22:46 +0100, David Bala?ic via Syslinux
wrote:
> Hi!
> I have bootable (USB flash) disk, that _appears_ to be using syslinux.
> (the word syslinux is in the PBR, in the hexdump).
> How can I chainload it? The payload seems to be a file that I tried
> load with COMBOOT, COM32 etc, but nothing works (they report that the
> file is not in proper format, wrong magic number or simply crash). How
> to proceed?
> 
I'm not sure how to chainload the PBR, but assuming that syslinux is in the
MBR,
you might be able to boot it with QEMU.

in BIOS MODE:
$ qemu-system-x86_64 -machine accel=kvm -m 512 -drive file=$MY_FILE,format=raw

or in UEFI MODE:
$ cp /usr/share/edk2/ovmf/OVMF_VARS.fd .
$ qemu-system-x86_64 -machine accel=kvm -m 512 -drive
if=pflash,format=raw,unit=0,file=/usr/share/edk2/ovmf/OVMF_CODE.fd,readonly=on
-drive if=pflash,format=raw,unit=1,file=OVMF_VARS.fd -drive
file=$MY_FILE,format=raw

If syslinux isn't in the MBR, you might be able to put it there by
dd'ing
(gpt)mbr.bin to the file/device like so:

# dd bs=440 count=1 conv=notrunc,sync if=/usr/share/syslinux/gptmbr.bin
of="$MY_FILE"

Substitute "$MY_FILE" with the image of the device you are trying to
boot.

You probably want to make a backup copy of your flash disk before writing
anything to it.

Use mbr.bin instead of gptmbr.bin if the partition table is in "msdos"
format.

Be sure that the partition that you are trying to chainload is set
active/bootable using your favorite partition managing tool.

Good luck.

On Tue, 17 Dec 2019 at 23:19, Gregory Lee Bartholomew <
gregory.lee.bartholomew at gmail.com> wrote:
> On Tue, 2019-12-17 at 22:46 +0100, David Bala?ic via Syslinux wrote:
> > Hi!
> > I have bootable (USB flash) disk, that _appears_ to be using syslinux.
> > (the word syslinux is in the PBR, in the hexdump).
> > How can I chainload it? The payload seems to be a file that I tried
> > load with COMBOOT, COM32 etc, but nothing works (they report that the
> > file is not in proper format, wrong magic number or simply crash). How
> > to proceed?
> >
>
> I'm not sure how to chainload the PBR, but assuming that syslinux is in
> the MBR,
> you might be able to boot it with QEMU.
>
I guess I was not clear enough.
The current state is:
MBR loads PBR which eventually loads the "app"

What I want is:
put grub2 on MBR (possibly also overwriting PBR) and in the grub2 menu add
an item the (chain)loads the previously mentioned "app" (there would
of
course be other menu items in grub2...)

Hope this is more clear now.

Regards,
David