UEFI subsystem
Lauching UEFI images
Bootefi command
The bootefi command is used to start UEFI applications or to install UEFI drivers. It takes two parameters
bootefi <image address> [fdt address]
- image address - the memory address of the UEFI binary
- fdt address - the memory address of the flattened device tree
The environment variable 'bootargs' is passed as load options in the UEFI system table. The Linux kernel EFI stub uses the load options as command line arguments.
Boot manager
The UEFI specification foresees to define boot entries and boot sequence via UEFI variables. Booting according to these variables is possible via
bootefi bootmgr [fdt address]
- fdt address - the memory address of the flattened device tree
The relevant variables are:
- Boot0000-BootFFFF define boot entries
- BootNext specifies next boot option to be booted
- BootOrder specifies in which sequence the boot options shall be tried if BootNext is not defined or booting via BootNext fails
Efidebug command
The efidebug command is used to set and display boot options as well as to display information about internal data of the UEFI subsystem (devices, drivers, handles, loaded images, and the memory map).
Initialization of the UEFI sub-system
Boot services
Image relocation
Memory services
Runtime services
Variable services
UEFI drivers
UEFI driver uclass
Block device driver
Protocols
Block IO protocol
File protocol
Graphical output protocol
Load file 2 protocol
The load file 2 protocol can be used by the Linux kernel to load the initial RAM disk. U-Boot can be configured to provide an implementation.