Not really on topic, and a quick google finds this:
http://docs.sun.com/app/docs/doc/817-5477/6mkuavhre?a=view
so .previous is accepted by Sun's x86 assembler. I can't see
any reference to .prefix in the Gnu assembler manual however
(google for "gnu gas manual") - so I guess the memtest86
people may well be using Sun's.
Since .previous just reselects the previous section it wouldn't
be difficult to edit the source (head.S) to manually reselect
the section.
BTW - the makefile uses head.s and head.S as separate files - so
to work under Cygwin you will need to use a managed mount.
-- Cliff
`.previous'
===========
This is one of the ELF section stack manipulation directives. The
others are `.section' (*note Section::), `.subsection' (*note
SubSection::), `.pushsection' (*note PushSection::), and `.popsection'
(*note PopSection::).
This directive swaps the current section (and subsection) with most
recently referenced section (and subsection) prior to this one.
Multiple `.previous' directives in a row will flip between two sections
(and their subsections).
In terms of the section stack, this directive swaps the current
section with the top section on the section stack.