r336876 breaks sysutils/acpi_call

A recent change in CURRENT has sysutils/acpi_call reliably cause a 
kernel panic when run on a Dell XPS laptop system.  I bisected this to 
r336876: Use SMAP on amd64.  I would have thought that this is a simple 
compatibility problem requiring only a port update, except that the same 
kernel and acpi_call on different hardware are not affected.  On the 
problematic system, the kernel module loads without incident; it is when 
executing ACPI commands, even normally harmless operations such as 
requesting read-only constants, that the system freeze occurs.  ACPI 
functionality seems otherwise unaffected.

Kernel debugging console and crash dumps are also broken on this system 
(I suspect due to Intel graphics) however it is an unrelated problem, 
and is only an excuse for my inability to provide any further crash 
information.

Having already bisected to the breaking commit, is there anything else I 
should do to improve the chances this problem gets fixed, or are there 
any hardware compatibility notes I may have missed?

Theron