For x86, building xen.efi requires gcc 4.5.x or above (4.6.x or newer recommended, as 4.5.x was probably never really tested for this purpose) and binutils 2.22 or newer. Additionally, the binutils build must be configured to include support for the x86_64-pep emulation (i.e. --enable-targets=x86_64-pep or an option of equivalent effect should be passed to the configure script).

For arm64, the PE/COFF header is open-coded in assembly, so no toolchain support for PE/COFF is required. Also, the PE/COFF header co-exists with the normal Image format, so a single binary may be booted as an Image file or as an EFI application. When booted as an EFI application, Xen requires a configuration file as described below unless a bootloader, such as GRUB, has loaded the modules and describes them in the device tree provided to Xen. If a bootloader provides a device tree containing modules then any configuration files are ignored, and the bootloader is responsible for populating all relevant device tree nodes.

Once built, make install-xen will place the resulting binary directly into the EFI boot partition, provided EFI_VENDOR is set in the environment (and EFI_MOUNTPOINT is overridden as needed, should the default of /boot/efi not match your system). The xen.efi binary will also be installed in /usr/lib64/efi/, unless EFI_DIR is set in the environment to override this default.

The binary itself will require a configuration file (names with the .efi extension of the binary's name replaced by .cfg, and - until an existing file is found - trailing name components dropped at ., -, and _ separators will be tried) to be present in the same directory as the binary. (To illustrate the name handling, a binary named xen-4.2-unstable.efi would try xen-4.2-unstable.cfg, xen-4.2.cfg, xen-4.cfg, and xen.cfg in order.) One can override this with a command line option (-cfg=<filename>). This configuration file and EFI commandline are only used for booting directly from EFI firmware, or when using an EFI loader that does not support the multiboot2 protocol. When booting using GRUB or another multiboot aware loader the EFI commandline is ignored and all information is passed from the loader to Xen using the multiboot protocol.

The configuration file consists of one or more sections headed by a section name enclosed in square brackets, with individual values specified in each section. A section named [global] is treated specially to allow certain settings to apply to all other sections (or to provide defaults for certain settings in case individual sections don't specify them). This file (for now) needs to be of ASCII type and not e.g. UTF-8 or UTF-16. A typical file would thus look like this (# serving as comment character):

**************************example begin******************************


options=console=vga,com1 com1=57600 loglvl=all noreboot
kernel=vmlinuz-3.0.31-0.4-xen ignore_loglevel #earlyprintk=xen

**************************example end********************************

The individual values used here are:


Specifies the section to use for booting, if none was specified on the command line; only meaningful in the [global] section. This isn't required; if absent, section headers will be ignored and for each value looked for the first instance within the file will be used.


Specifies the options passed to the hypervisor, see Xen Hypervisor Command Line Options.

kernel=<filename>[ <options>]

Specifies the Dom0 kernel binary and the options to pass to it.


Specifies a Linux-style initial RAM disk image to load.

Other values to specify are:


Specifies a video mode to select if available. In case of problems, the -basevideo command line option can be used to skip altering video modes.


Specifies an XSM module to load.


Specifies a CPU microcode blob to load. (x86 only)


Specifies a device tree file to load. The platform firmware may provide a DTB in an EFI configuration table, so this field is optional in that case. A dtb specified in the configuration file will override a device tree provided in the EFI configuration table. (ARM only)


Specifies an alternate configuration file to use in case the specified section (and in particular its kernel= setting) can't be found in the default (or specified) configuration file. This is only meaningful in the [global] section and really not meant to be used together with the -cfg= command line option.

Filenames must be specified relative to the location of the EFI binary.

Extra options to be passed to Xen can also be specified on the command line, following a -- separator option.