[syslinux] kexec to syslinux

Jorge Almeida jjalmeida at gmail.com
Tue Feb 14 13:17:21 PST 2017

On Tue, Feb 14, 2017 at 10:58 AM, H. Peter Anvin <hpa at zytor.com> wrote:
> On 02/08/17 06:33, Jorge Almeida via Syslinux wrote:
>> Is it possible to kexec to the syslinux interface, thus bypassing the
>> hw initialization?
>> What would be the kexec command?
>> kexec -l ??? --append=???   --initrd=???
> It is theoretically possible but is likely to break on many systems.
> To boot it from a raw disk (the normal operation for Syslinux) would
> require a small amount of software which currently doesn't exist, but
> you can test it using a disk image and using MEMDISK:
> kexec -l memdisk --initrd=disk.img --real-mode

This may well be above my amateur head, but anyway I tried downloading
al alpine iso, and then:

kexec -l /boot/syslinux/memdisk
--initrd=/boot/alpine-standard-3.5.1-x86_64.iso --real-mode
--append="iso raw"

(I tried first without "raw", just "iso".)

The console says "kexec_cores: Starting new kernel"

and hangs forever.

BTW: I also tried an entry for alpine in syslinux.cfg:

LABEL alpine
    MENU LABEL Alpine
    LINUX memdisk
    INITRD ../alpine-standard-3.5.1-x86_64.iso
    APPEND iso

It doesn't boot, it appears an unusable emergency shell (doesn't react to keys).

Of course, the alpine iso may not be suitable for this stuff, it's
just what I got on short notice small enough to fit my /boot

About "disk.img", I don't know what to do. I currently don't use an
initramfs (Gentoo is my usual system). Any downloadable suitable disk
image out there?

> If this actually works and is useful it would be a quick hack to add the
> missing piece.
> This will not work on UEFI platforms; there is no way to revert to UEFI
> boot mode without a system reset.
I intend to keep away from UEFI as long as possible...


Jorge Almeida

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