CVS commit: src/sys/arch/amd64/amd64

["Maxime Villard" <maxv%netbsd.org@localhost>]

Module Name:    src
Committed By:   maxv
Date:           Fri Mar 24 18:03:32 UTC 2017

Modified Files:
        src/sys/arch/amd64/amd64: amd64_trap.S

Log Message:
Unconditionnally save the segment registers - because we could have a
kernel %gs and a userland %es/%ds -, and explain why T_NMI is a special
case.

Note that checking %gs directly is not a good idea: recent CPUs have the
FSGSBASE instruction set, which allows userland to directly modify %gs
without going through the kernel. If we ever enable this set, we will have
to change this function, since we won't be able to test %gs against
VM_MIN_KERNEL_ADDRESS anymore.


To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/sys/arch/amd64/amd64/amd64_trap.S

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.