recent change to binutils' include/opcode/i386.h

H. J. Lu
Fri Jul 23 14:00:00 GMT 2004

On Fri, Jul 23, 2004 at 08:53:36AM +0200, Jan Beulich wrote:
> H.J.,
> it would seem to me that the change to again allow cs/ds prefixes in
> 64-bit mode should be undone. If you want branch prediction hints, use
> the ,ht and ,hn instruction suffixes. Using segment overrides in their
> place is counter intuitive, and generally allowing them in 64-bit mode
> is an error in any case (if you absolutely wanted to allow them for this
> specific purpose, then you'd have to add checks in other places
> preventing incorrect uses).

All the current gccs in CVS and released versions use "cs/ds ;" as
branch hints for EM64T. You can see that by passing -march=nocona to
gcc 3.3, 3.4 and 3.5 for x86-64. Assembler has to support it. As far
as I know, all x86-64 chips can handle segment prefixes. Whether they
do anyhing useful is entirely a different question.

If you think it may be an error in some other places, please show me
the document and feel free to submit a patch. But please make sure
cs/ds can still be used as branch hints for EM64T. We can't break
gcc because of it.


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