Re: Lets talk to each other...

["J. Kean Johnston" <jkj at sco dot com>]

On Mon, Sep 27, 1999 at 03:26:12PM -0700, H.J. Lu wrote:
> I agree. When I made changes to x86 FPU for gdb 4.17, I compiled
Actually everything worked quite fine on 4.18 ... it was more recent
changes (see below) that did it. But I am working on bringing the
SCO OSes up to speed.

Fri Sep  3 00:47:44 1999  Kevin Buettner  <kevinb@cygnus.com>

There is actually quite a bit of stuff in there that is really Linux
specific (and the abstraction that was done assumed similar functionality
on all other OSes). One particular problem for me is that on OSR5, the
FPU registers are not stored with the normal registers. We do some
optimization in the contexct switch code to only save the FPU registers if
they were used. They get stored in a different part of the u_area structure,
so there isn't easy, contiguous register access from eax all the way down
to the FPU registers. In fact, to make my life more difficult, the way
we DO store registers in the u_area is a bit weird, with ds, es, ss and cs
at the top of the u_area, followed later by eax, ebx etc. Part of the reason
for all this bullshit is that we do not use the CPU to switch tasks through
the TSS. Rather, we do a manual software switch, which is MUCH faster than
using the CPU to do the context switch (by several hundred cycles). Needless
to say all of those cycles add up :-)

Anyway ... this is not an insurmountable problem and I will have a patch
soon. I actually suspect that in days gone by, that even though GDB was
compiling and sorta-working on OSR5, that close inspection of the
registeres would actually have shown incorrect values. So in a way this is
good coz now I can fix it and make it do The Right Thing. Not sure what
the implications for UnixWare are (or any of the low level detains on its
switching ... I havent looked at that part of the kernel yet).

-- 
J. Kean Johnston  | "Only the dead have seen an end to war"
Engineer, SPG     |                                         -- Plato
Santa Cruz, CA    +----------------------------------------------------------
Tel: 831-427-7569    Fax: 831-429-1887    E-mail: jkj@sco.com