How to kexec a xen kernel; when I kexec a xen kernel it is throwing memory errors

[A Kundu <avikalpa@xxxxxxxxx>]

$ uname -a
Linux host 6.9.10-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.9.10-1 
(2024-07-19) x86_64 GNU/Linux
$ kexec --version
kexec-tools 2.0.29

XEN_HYPERVISOR="/boot/xen.gz"
XEN_CMD="dom0_mem=6G dom0_max_vcpus=6 dom0_vcpus_pin cpufreq=xen"

In case of 4.19-rc4
# kexec -l "$XEN_HYPERVISOR" --command-line="$XEN_CMD"
Could not find a free area of memory of 0x3b6001 bytes...
elf_exec_build_load_relocatable: ELF exec load failed

In case of 4.20-dev
# kexec -l "$XEN_HYPERVISOR" --command-line="$XEN_CMD"
Could not find a free area of memory of 0x3f8001 bytes...
elf_exec_build_load_relocatable: ELF exec load failed

Then I followed the xen manual on:
https://xenbits.xenproject.org/docs/4.19-testing/misc/kexec_and_kdump.txt

# Set variables
XEN_IMAGE="/boot/xen-4.19-rc.gz"
DOM0_IMAGE="/boot/vmlinuz-6.9.10-amd64"
DOM0_INITRD="/boot/initrd.img-6.9.10-amd64"
DOM0_MEMORY="6G"
DOM0_CPUS="0-5"

# Prepare Xen and dom0 command line arguments
XEN_ARGS="no-real-mode dom0_mem=${DOM0_MEMORY}"
DOM0_ARGS="max_cpus=6 dom0_max_vcpus=6 dom0_vcpus_pin"

# Load Xen and dom0 kernel
kexec -l --append="${XEN_ARGS} -- ${DOM0_ARGS}" --initrd=${DOM0_INITRD} \
  --vmm=${XEN_IMAGE} ${DOM0_IMAGE}
kexec: unrecognized option '--vmm=/boot/xen-4.19-rc.gz'
kexec-tools 2.0.29

kexec-tools 2.0.29 does not know vmm; this by a compiled from
a source tarball with ./configure --with-xen

The same is the case for the apt version of kexec-tools.