Mail Archives: djgpp/1996/12/29/21:00:51
Once upon a time (on 26 Dec 96 at 17:17) Paul Cunningham said:
> I've written a thread package using djgpp. It works fine at the
> moment but I was wondering if its necessary to save the section
> registers, EG. %cs %ds %ss %es %fs and %gs when I swap threads.
It depends on some factors. If you allocate separate stacks for every
thread then yes, you have to save %ss among switches. %cs doesn't
change unless you allocate separate segment (btw. there's no such
thing as 'section' in Intel CPU nomenclature) for every thread. %es &
%fs should be saved since you cannot tell whether any of the threads
uses them or not (and DJGPP libc uses them at times - esp. %es).
%gs is rather unlikely to be used, but better be safe than sorry ;-))
%ds should be saved for the same reason %es is.
> As I said, it works fine with all the tests I've thrown at it
> without saving them and just using their current values but I'm not
> sure if they change in certain circumstances.
Oh yes! They change. %es is being used in all the string operations.
%fs is used when emulating far pointers, %ds might be used to access
various segments out of the common 'flat' one used by default. %ss
changes everytime any RMCB is called and at many other times.
So the conclusion is: save them.
_http://ananke.amu.edu.pl/~grendel_________________________
We buy fresh bagels from the corner store where swastikas
are spat from areosols. I sit in the bar sipping iced white
russians, trying to score but nobody's pushing. And everyone
looks at everyone's faces, searching for signs and praying
for traces of a conscience in residence, are we sitting on
a barbed wire fence chasing the clouds home?
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