Can we do segment-override any way we want in Intel 64 mode(IA-32e)?

Is the following assembly line valid?
mov SS:, EAX

Posted on 2010-05-15 01:52:29 by logicman112
Posted on 2010-05-15 13:12:56 by SpooK
If an instruction uses base registers RSP/RBP and uses a segment override prefix to
specify a non-SS segment, a canonical fault generates a #GP (instead of an #SF). In
64-bit mode, only FS and GS segment-overrides are applicable in this situation.
Other segment override prefixes (CS, DS, ES and SS) are ignored. Note that this also
means that an SS segment-override applied to a “non-stack” register reference is
ignored.

I copied some lines from Intel manual in the above. What do they mean? Overriding segments in 64-bit mode some has some limits? 
Posted on 2010-05-30 23:41:29 by logicman112
When using SS results in addressing outside of the canonical range, it generates #SS.

When using FS or GS results in addressing outside of the canonical range, it generates #GP.
Posted on 2010-05-31 00:11:59 by SpooK
In short, it means that you shold use SS with 'stack' GP registers (sp/bp) for stack instructions and other segment registers with other non-stack GP registers for other instructions :P Makes sense, huh? ;) Otherwise you may get non-intuitive faults.
Posted on 2010-05-31 00:16:16 by ti_mo_n