Kernel configuration

What is an EFI stub?
An EFI stub is a kernel in the form of an EFI executable which can be directly booted from UEFI firmware.

Is a bootloader required for EFI stubs?
No, a bootloader isn't required for EFI stubs.

What kernel configuration options must be enabled for EFI stub support?
The kernel configuration options that must be enabled for EFI stub support are:

  • EFI runtime service support (CONFIG_EFI).
  • EFI stub support (CONFIG_EFI_STUB).
  • EFI mixed-mode support (CONFIG_EFI_MIXED) - This setting is only required if you're booting a 64-bit kernel from 32-bit firmware, the CPU supports 64-bit mode, and EFI handover is enabled.

Installation

What partition do you have to create in order to use an EFI stub?
The partition you have to create in order to use an EFI stub is an EFI System Partition (ESP).

Automated

What should you keep in mind with EFI stub booting and different UEFI vendors?
With EFI stub booting and different UEFI vendors, you should keep in mind that it's not guaranteed to work for all UEFI systems.

What package provides automated EFI stub booting?
The package that provides automated EFI stub booting is sys-kernel/installkernel-38.

What USE flag needs to be enabled in order for installkernel-38 to set up EFI stub booting?
In order for installkernel-38 to set up EFI stub booting, the USE flag that needs to be enable is the efistub USE flag.

What does installkernel-38 do when the efistub USE flag is enabled?
When the efistub USE flag is enabled, installkernel-38 relocates the regular boot layout from /boot to the EFI/Gentoo directory on the ESP.

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