[syslinux] Booting legacy Linux kernel in EFI mode

[Celelibi]

2013/9/24, Gene Cumm <gene.cumm at gmail.com>:
> On Sun, Sep 22, 2013 at 3:09 PM, Celelibi <celelibi at gmail.com> wrote:
>> Hello,
>>
>> My question is quite straightforward, still I couldn't find an anwser
>> on the interweb.
>> Is it possible to boot the Linux kernels I used to boot in legacy
>> mode, but now in EFI mode?
>
> I believe unless the kernel specifically supports EFI boot, it can not
> be booted.
>
>> I mean, I would like to keep all my PXE settings with my menus and
>> kernels and stuff, but now boot them in PXE-EFI mode.
>>
>> I've been able to boot on syslinux.efi and keep my config files, but
>> when I try to boot on a linux kernel, I get an error like "no such
>> file or directory" while I see it download the file from the tftp.
>>
>> Is this a bug in syslinux?
>> Or is there a deep incompatibility?
>> And (a bit out of scope) if I get my old kernel to boot in EFI mode,
>> will the driver efivars have access to the EFI variables? Or does the
>> kernel need to be recompiled specially for EFI?
>
> Doubtful.  Yes (although I think most EFI kernels I've seen will
> function for both).
>
> --Gene
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>


Sorry for answering that late. (I had some issues with my server's
Ethernet NIC, and without it, no PXE / syslinux.)

So, it's time to be a bit more specific.
The kernel I want to boot in EFI mode is a debian installer. It *has*
a module "efivars" loaded. Which means this kernel has been compiled
with CONFIG_EFI_VARS, which itself depends on CONFIG_EFI. Therefore I
should be able to boot this kernel in EFI mode.

I don't remember whether I tried or not, so I'll re-test ASAP.
However, as I discussed on IRC, the 'file' command only say "x86 boot sector".


Celelibi