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Report on MMX support on Linux
Following my own question some while ago, that no-one here seemed to be
able to answer:
1. The Intel documentation on MMX says that:
"MMX technology retains its full compatibility with existing operating
systems and applications by aliasing its registers and state upon the IA
floating-point registers and state. Therefore, no new registers or states
are added to support MMX technology. This means that the operating system
uses the standard mechanisms for interacting with the floating point state
to save and restore MMX code."
Thus, MMX or FPU calculations will not be damaged when the process or
thread is cut by the micro-kernel, and the Linux kernel (or any other
kernel for that matter) need not be changed accordingly. Note, that it is
still up to the programmer or compiler not to interlace MMX and FPU
calculations.
2. Assembly code that contains MMX instructions can be generated by a
compiler called NASM, that uses the Intel-syntax rather than the AT&T
syntax used by GNU as and gcc.
3. PentiumGCC is a version of egcs that generates optimized code for the
Pentium family of microprocessors. It is expected to be able to generate
MMX-optimized code for the Pentium-II chips in one of its next releases.
4. Judging by #3, I conclude that GNU as supports MMX on PII, but not
on normal Pentium+MMX. I suppose one can patch its source manually to
achieve this end.
5. One can embed MMX instructions inside the Linux Kernel, if it is
compiled for PII and is supposed to run on it.
Shlomi Fish
BTW, why are there still problems when sending mail to
linux-il@linux.org.il? The mail reaches taragon.tcltek.co.il and then
is bounced back by the qmail daemon that is running there.
----------------------------------------------------------------------
Shlomi Fish shlomif@vipe.technion.ac.il
Home Page: http://t2.technion.ac.il/~shlomif/
Home E-mail: shlomif@ibm.net
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