Grub2 + Xen + DomU Kernel = not xen image

[Shaun Reitan]

I've built a grub2 image mainly based on the wiki article on 
https://wiki.xenproject.org/wiki/PvGrub2

My image has been working great for years, however it seams that 
debian/ubuntu has changed some things in it's newer releases and now my 
pvgrub image is dumping the error "not xen image".  I'm not the first 
one who's seen this as i've found one other person with this issue.  
Their solution was to move to pvh but unfortunately that's currently not 
an option.  It would appear that the issue has to do with LZ4 compressed 
images according to the other ML post i found.

Inside my ubuntu image when I run file on the kernel it comes back as

vmlinuz-5.4.0-72-generic: Linux kernel x86 boot executable bzImage, 
version 5.4.0-72-generic (buildd@lcy01-amd64-019) #80-Ubuntu SMP Mon Apr 
12 17:35:00 UTC 2021, RO-rootFS, swap_dev 0xB, Normal VGA

and when I run file on the initrd image it comes back as
initrd.img-5.4.0-72-generic: LZ4 compressed data (v0.1-v0.9)

I'm at a loss right now as to what is causing the issue and how to fix 
it.  When i enable debuging in grub the is the output I get.

==== GRUB DEBUG ====
linux /boot/vmlinuz-5.4.0-72-generic
script/lexer.c:336: token 288 text [linux]
script/script.c:50: malloc 0x13e996c60
script/script.c:50: malloc 0x13e996c20
script/script.c:163: arglist
script/script.c:50: malloc 0x13e996bc0
script/lexer.c:336: token 289 text [/boot/vmlinuz-5.4.0-72-generic]
script/script.c:50: malloc 0x13e996900
script/script.c:50: malloc 0x13e9968a0
script/script.c:163: arglist
script/script.c:50: malloc 0x13e996840
script/lexer.c:336: token 259 text [
]
script/script.c:50: malloc 0x13e9967e0
script/script.c:50: malloc 0x13e9967a0
script/script.c:198: cmdline
script/script.c:50: malloc 0x13e996740
script/lexer.c:336: token 0 text []
script/script.c:50: malloc 0x13e996dc0
script/script.c:50: malloc 0x13e996d80
script/script.c:294: append command
script/script.c:50: malloc 0x13e996d40
commands/wildcard.c:535: no expansion needed
commands/wildcard.c:594: paths[0] = `/boot/vmlinuz-5.4.0-72-generic'
kern/disk.c:196: Opening `xen/xvda'...
kern/xen/init.c:227: msg type = 2, len = 8
kern/xen/init.c:227: msg type = 2, len = 3
kern/fs.c:56: Detecting zfs...
fs/zfs/zfs.c:1196: label ok 0
fs/zfs/zfs.c:1196: label ok 1
fs/zfs/zfs.c:1196: label ok 2
fs/zfs/zfs.c:1196: label ok 3
kern/fs.c:78: zfs detection failed.
kern/fs.c:56: Detecting xfs...
fs/xfs.c:909: Reading sb
fs/xfs.c:258: Validating superblock
kern/fs.c:78: xfs detection failed.
kern/fs.c:56: Detecting ufs2...
kern/fs.c:78: ufs2 detection failed.
kern/fs.c:56: Detecting ufs1_be...
kern/fs.c:78: ufs1_be detection failed.
kern/fs.c:56: Detecting ufs1...
kern/fs.c:78: ufs1 detection failed.
kern/fs.c:56: Detecting udf...
kern/fs.c:78: udf detection failed.
kern/fs.c:56: Detecting tarfs...
kern/fs.c:78: tarfs detection failed.
kern/fs.c:56: Detecting squash4...
kern/fs.c:78: squash4 detection failed.
kern/fs.c:56: Detecting sfs...
kern/fs.c:78: sfs detection failed.
kern/fs.c:56: Detecting romfs...
kern/fs.c:78: romfs detection failed.
kern/fs.c:56: Detecting reiserfs...
kern/fs.c:78: reiserfs detection failed.
kern/fs.c:56: Detecting odc...
kern/fs.c:78: odc detection failed.
kern/fs.c:56: Detecting ntfs...
kern/fs.c:78: ntfs detection failed.
kern/fs.c:56: Detecting nilfs2...
kern/fs.c:78: nilfs2 detection failed.
kern/fs.c:56: Detecting newc...
kern/fs.c:78: newc detection failed.
kern/fs.c:56: Detecting minix_be...
kern/fs.c:78: minix_be detection failed.
kern/fs.c:56: Detecting minix3_be...
kern/fs.c:78: minix3_be detection failed.
kern/fs.c:56: Detecting minix3...
kern/fs.c:78: minix3 detection failed.
kern/fs.c:56: Detecting minix2_be...
kern/fs.c:78: minix2_be detection failed.
kern/fs.c:56: Detecting minix2...
kern/fs.c:78: minix2 detection failed.
kern/fs.c:56: Detecting minix...
kern/fs.c:78: minix detection failed.
kern/fs.c:56: Detecting jfs...
kern/fs.c:78: jfs detection failed.
kern/fs.c:56: Detecting iso9660...
kern/fs.c:78: iso9660 detection failed.
kern/fs.c:56: Detecting hfsplus...
kern/fs.c:78: hfsplus detection failed.
kern/fs.c:56: Detecting hfs...
kern/fs.c:78: hfs detection failed.
kern/fs.c:56: Detecting fat...
kern/fs.c:78: fat detection failed.
kern/fs.c:56: Detecting f2fs...
kern/fs.c:78: f2fs detection failed.
kern/fs.c:56: Detecting ext2...
commands/verifiers.c:88: file: /boot/vmlinuz-5.4.0-72-generic type: 3
[ vmlinuz-5.4.0-72-gen  10B  0%  0.00B/s ] loader/i386/xen_file.c:65: 
found bzimage payload 0x4bb1-0xaf3166
kern/disk.c:295: Closing `xen/xvda'.
error: not xen image.
script/script.c:65: free 0x13e996d40
script/script.c:65: free 0x13e996d80
script/script.c:65: free 0x13e996dc0
script/script.c:65: free 0x13e996740
script/script.c:65: free 0x13e9967a0
script/script.c:65: free 0x13e9967e0
script/script.c:65: free 0x13e996840
script/script.c:65: free 0x13e9968a0
script/script.c:65: free 0x13e996900
script/script.c:65: free 0x13e996bc0
script/script.c:65: free 0x13e996c20
script/script.c:65: free 0x13e996c60