x86 FRED: add hardware definitions for the trap frames fields

[kib]

Summary

as provided by the Intel document 346446-009 AKA FRED 8.0.

[markj]

sys/amd64/amd64/trap.c

944

No need anymore for the mask of tf_cs.

sys/x86/include/frame.h

148

The field prefix should be tf_.

152–157

Should we apply some explicit masking in places where tf_ss is assigned by software? e.g. in set_mcontext(), we have tp->tf_ss = mcp->mc_ss, so there is implicit truncation.

154

The numbering of the evinfo fields is a bit weird. I see why you did it this way, it follows the order that the fields are described in the FRED documentation. Probably not worth changing.

[kib]

sys/x86/include/frame.h

152–157

I do not object, but I do not see a purpose for explicit cast or masking.
OTOH we indeed might consider adding checks that ss cs from the mcontext fits into 16 bits, i.e. the reserved bits are not passed by userspace.

[kib]

Fix typo in the name of the reserved field.
Remove cs masking.

[markj]

sys/x86/include/frame.h

152–157

Some checks would be good. I'm not sure if there is any chance that they would break compatibility somehow.