[Bug 284460] smbios driver does not discover the 64-bit table on BIOS boot

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=284460

            Bug ID: 284460
           Summary: smbios driver does not discover the 64-bit table on
                    BIOS boot
           Product: Base System
           Version: CURRENT
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: andreas.rogge@bareos.com

I noticed that when running FreeBSD on the Hetzner Cloud since January 16th
SMBIOS information is not available via kenv.
As the cloud-init provider for Hetzner relies on smbios.system.maker and
smbios.system.serial being available, this also breaks cloud-init.

Investigating further, I noticed they provide a 64-bit SMBIOS table without
providing a 32-bit compatibility table. While the standard strongly suggests to
provide a 32-bit table, it is not required.

The smbios driver can already handle the 64-bit table when being booted via
UEFI, but these cloud machines are BIOS booted and the driver currently simply
does not look for the 64-bit table.
It does a bios_sigsearch() for "_SM_" (the 32-bit table), but does not try
"_SM3_" (the 64-bit table) if that fails.

Basically, adding the following after sys/dev/smbios/smbios.c:107 should fix
the problem:
--- CUT HERE ---
if (addr == 0) {
  map_size = sizeof (*eps3);
  addr = bios_sigsearch(SMBIOS_START, SMBIOS3_SIG, SMBIOS3_LEN,
                        SMBIOS_STEP, SMBIOS_OFF);
}
--- CUT HERE ---

However, I haven't tested this yet.

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