[syslinux] Is chain loading EFI apps not supported?

[Frantisek Rysanek]

On 20 Mar 2023 at 0:00, marteg via Syslinux wrote:
>
> Greetings!
> 
> If I understand everything correctly, the last release of syslinux 
> supports UEFI, but it can't load another EFI application in this mode, so 
> practically only linux kernel can be bootloaded. Unfortunately, I have a 
> need to dualboot windows and linux with UEFI, and this holds me back from 
> using this amazing piece of software.
> Have there since been any progress regarding this issue? Are there any 
> plans to implement this in the future? Can I help somehow?
> 
> Sincerely,
> Martynenko Egor
>
I've been a user of ISOLINUX and PXELINUX (and also sometimes 
syslinux) for almost two decades.
Syslinux has been an excellent piece of software - very good at the 
job it's been doing.
That said, sadly, its development has stalled years ago, HPA and the 
team don't seem to be adding any commits.

For your needs, have you tried rEFInd maybe?
https://sourceforge.net/projects/refind/

Instead of / in parallel to PXElinux, I've been using iPXE for a 
while (after someone's suggestion in this mailing list, years ago).
Not sure if iPXE could possibly be used on a hard drive :-)

If dual-booting Windows and Linux off a hard drive is the final goal, 
I'm a bit afraid that Windows would keep "correcting" the "bootloader 
arrangement" to have the system boot Windows only. Perhaps with a 
small USB stick (dedicated to your rEFInd boot loader) you could 
achieve you goal, while Windows would be happy too (not sure).

Some BIOS/UEFI firmwares out there have a dedicated "boot override 
menu" on a shortcut key combo = besides the full-blown SETUP app.
Not sure if you can have multiple "EFI-bootable" partitions on a 
single hard drive, or if the UEFI FW is prepared to look for 
something like this. Perhaps adding a second HDD would give you a 
better chance to achieve this, in a generic fashion.
IIRC, rEFInd has its own way of dealing with multi-boot hard drives.

Frank