[Bug 273814] sysutils/grub2-bhyve: fails to boot OpenBSD Current kernel

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=273814

            Bug ID: 273814
           Summary: sysutils/grub2-bhyve: fails to boot OpenBSD Current
                    kernel
           Product: Ports & Packages
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: Individual Port(s)
          Assignee: ports-bugs@FreeBSD.org
          Reporter: naito.yuichiro@gmail.com

Created attachment 244872
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=244872&action=edit
grub2-bhyve.patch

By the following commit, OpenBSD Current kernel has dropped supporting old
console device structure. It causes grub-bhyve not to boot the OpenBSD Current
kernel. The new release 7.4 is coming soon will also unbootable from the
current grub2-bhyve.

https://github.com/Openbsd/src/commit/745c2f60e98fd1f418c104960a567e120624d705

I wrote a patch for this problem that changes to use the new console device
structure by default. And my patch switches to use the old console device
structure if the loading kernel is older than '7.3' release.

The version number is written in the value of 'osrelease' symbol in the OpenBSD
kernel. My patch reads it to see if the kernel is older than '7.3' or not.
All the previous releases contain symbol tables, so no problem. If users strip
the OpenBSD kernel, reading the version number will fail. I added 'kopenbsd -l'
option to force to use the old console device structure. If users boot the
OpenBSD Current or newer kernel, just 'kopenbsd' command works fine although
the kernel is stripped. Because the new console device structure is chosen by
default.

Implementation Note: (record for maintainers)

Reading symbol tables is already implemented in 'grub_openbsd_find_ramdisk'
function. I added reading the value of 'osrelease' symbol in this function to
share the symbol lookup code. And building console device structure is
implemented in 'grub_cmd_openbsd' function, but it is called earlier than
'grub_openbsd_find_ramdisk' function. So 'grub_cmd_openbsd' function never
knows the version number. I changed to build both the new and old console
device
structures in 'grub_cmd_openbsd'. They are added to 'tag' list and
'grub_openbsd_boot' function reads the 'tag' list and build stack frame that is
passed to OpenBSD kernel. I changed the building stack frame code to ignore
unnecessary console device structure checked by the 'osrelease' value.

I also added 'openbsd_force_legacy_console' global variable. It's a flag to
force to use the old console device structure. This flag is set by '-l' option.

Testing: 

My poudriere build successfully finished with my patch. And I confirmed my
patch
booted OpenBSD kernel from 6.9 to 7.3 and Current successfully. And also the
installers of OpenBSD 6.9 - 7.3 was booted successfully.

Please apply the attached 'grub2-bhyve.patch' to Ports tree.

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