kern/51988: boot fails very early with amd64

[mlelstv%serpens.de@localhost]

>Number:         51988
>Category:       kern
>Synopsis:       boot fails very early with amd64
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 21 01:45:00 +0000 2017
>Originator:     Michael van Elst
>Release:        NetBSD 7.99.60
>Organization:
	
>Environment:
	
	
System: NetBSD tazz 7.99.60 NetBSD 7.99.60 (TAZZ) #15: Tue Feb 21 01:59:35 CET 2017 mlelstv@gossam:/home/netbsd-current/obj.amd64/home/netbsd-current/src/sys/arch/amd64/compile/TAZZ amd64
Architecture: x86_64
Machine: amd64
>Description:
Current no longer boots on a Thinkpad T420 with Core-i5 CPU.

After load the kernel, the display shows garbage and the machine resets.

Bisecting the commits of the last two weeks identifies:

Sat Feb 11 16:02:11 UTC 2017 maxv
   | src/sys/arch/amd64/conf: Makefile.amd64 kern.ldscript
 Put 2MB alignments between the kernel segments. This way the kernel image
 is entirely mapped with large pages, which uniformizes performance and
 reduces fluctuation. Sent on port-amd64.

as the culprit. Revoking that commit makes the kernel boot and work again.

>How-To-Repeat:
Boot current on a Thinkpad T520 with

cpu0: "Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz"

>Fix:
	

>Unformatted: