On Tue, Apr 10, 2001 at 12:42:07PM -0700, Linus Torvalds wrote:
>
>
> On Tue, 10 Apr 2001, David Howells wrote:
> >
> > Here's a patch that fixes RW semaphores on the i386 architecture. It is very
> > simple in the way it works.
>
> XADD only works on Pentium+.
My Intel manual says it 486+:
``
XADD-Exchange and Add
[...]
Intel Architecture Compatibility
Intel Architecture processors earlier than the Intel486TM processor do not recognize
this instruc-
tion. If this instruction is used, you should provide an equivalent code sequence that
runs on
earlier processors.
''
I guess 386 could live with an exception handler that emulates it.
(BTW an generic exception handler for CMPXCHG would also be very useful
for glibc -- currently it has special checking code for 386 in its mutexes)
The 386 are so slow that nobody would probably notice a bit more slowness
by a few exceptions.
-Andi
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