Syslinux - Oct 2013 - Booting legacy Linux kernel in EFI mode

On Tue, Sep 24, 2013 at 11:57 PM, Gene Cumm <gene.cumm at gmail.com>
wrote:
> On Sun, Sep 22, 2013 at 3:09 PM, Celelibi <celelibi at gmail.com>
wrote:
>> 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).

    Just to be clear, it requires enabling of `CONFIG_EFI_STUB`
configuration variable right?

    Because although I'm using one of the pre-release versions of
`6.02` which should support x32 kernel loading (with x64 UEFI) it
still doesn't work for me.  (Although I haven't fiddle too much with
it.)

    Ciprian.

2013/9/26, Ciprian Dorin Craciun <ciprian.craciun at
gmail.com>:
> On Tue, Sep 24, 2013 at 11:57 PM, Gene Cumm <gene.cumm at gmail.com>
wrote:
>> On Sun, Sep 22, 2013 at 3:09 PM, Celelibi <celelibi at gmail.com>
wrote:
>>> 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).
>
>
>     Just to be clear, it requires enabling of `CONFIG_EFI_STUB`
> configuration variable right?
>
>     Because although I'm using one of the pre-release versions of
> `6.02` which should support x32 kernel loading (with x64 UEFI) it
> still doesn't work for me.  (Although I haven't fiddle too much
with
> it.)
If I understood correctly, CONFIG_EFI_STUB only allows you to boot
your kernel as an EFI executable. That is, you can copy it to the
FAT32 partition and run vmlinuz.efi. See
Documentation/x86/efi-stub.txt.
But I don't know about x32 and x64 behavior. Why don't you use a
64bits kernel with your x64 UEFI?

Celelibi

On Wed, Oct 16, 2013 at 6:41 PM, Celelibi <celelibi at gmail.com>
wrote:
> 2013/9/26, Ciprian Dorin Craciun <ciprian.craciun at gmail.com>:
>> On Tue, Sep 24, 2013 at 11:57 PM, Gene Cumm <gene.cumm at
gmail.com> wrote:
>>> On Sun, Sep 22, 2013 at 3:09 PM, Celelibi <celelibi at
gmail.com> wrote:
>>>> 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).
>>
>>
>>     Just to be clear, it requires enabling of `CONFIG_EFI_STUB`
>> configuration variable right?
>>
>>     Because although I'm using one of the pre-release versions of
>> `6.02` which should support x32 kernel loading (with x64 UEFI) it
>> still doesn't work for me.  (Although I haven't fiddle too much
with
>> it.)
>
> If I understood correctly, CONFIG_EFI_STUB only allows you to boot
> your kernel as an EFI executable. That is, you can copy it to the
> FAT32 partition and run vmlinuz.efi. See
> Documentation/x86/efi-stub.txt.
> But I don't know about x32 and x64 behavior. Why don't you use a
> 64bits kernel with your x64 UEFI?
It's about options.  If an x64 UEFI can boot an IA32 kernel, you don't
need two on your PXE system.

Like Ciprian, I can't boot an IA32 kernel from my x64 UEFI with
Syslinux EFI64, even though both can do BIOS and EFI boot.

-- 
-Gene

On 10/16/2013 03:41 PM, Celelibi wrote:
> 
> If I understood correctly, CONFIG_EFI_STUB only allows you to boot
> your kernel as an EFI executable. That is, you can copy it to the
> FAT32 partition and run vmlinuz.efi. See
> Documentation/x86/efi-stub.txt.
> But I don't know about x32 and x64 behavior. Why don't you use a
> 64bits kernel with your x64 UEFI?
> 
It is also the preferred entry path into the kernel when the kernel is
loaded by a bootloader.

	-hpa