About
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If your Xen system is based on UEFI with the ESP mounted on /boot/efi, you
will get a linking error when trying to install a hypervisor like:
xen-hypervisor-4.20-amd64_4.20.0-1+deb12u3.8_amd64.deb

Your ESP mount is similar to below:
UUID=26F1-4BDA	/boot/efi	vfat	rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro	0	2

Workaround
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This trick proposes to manually install the included *.efi into /boot/efi, unmount
the ESP (boot/efi), do a normall install, finally remount ESP.

to extract the *.efi from the hypervisor package:

// ar, install binutils
apt install binutils
man ar

mkdir zztemp && cd $_
dpkg -x ../xen-hypervisor-4.20-amd64_4.20.0-1+deb12u3.8_amd64.deb ./

above works, but it extracts the whole package to curdir. A more compact
way is to use ar (with the hypervisor above):

ar -xv ../xen-hypervisor-4.20-amd64_4.20.0-1+deb12u3.8_amd64.deb
x - debian-binary
x - control.tar.xz
x - data.tar.xz

the *.deb are in data.tar.xz, and we can access precisely the *.efi like this:

tar -xf data.tar.xz --wildcards */*efi --strip-components 5
xen-4.20-amd64.efi
xen-4.20-xsm.efi

While the ESP is mounted to /boot/efi :
sudo cp -p *.efi /boot/efi/EFI/debian

To continue with the install of the new xen release, we have to unmount the ESP
sudo unmount /boot/efi

sudo apt install ./*.deb

After above succeeds:
sudo mount /boot/efi
sudo systemctl daemon-reload


Author
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PryMar56
June 2025