Re: -mno-sse and -mno-sse2 broken on opteron?

[Marcin Dalecki <martin at dalecki dot de>]

On 2005-01-07, at 00:41, Richard Henderson wrote:

> On Thu, Jan 06, 2005 at 08:44:36PM +0100, Marcin Dalecki wrote:
> > That's a non issue. You simply don't use floating point arithmetics
> > when for kernels.
>
> How naieve you are.  The compiler is getting smart enough to use
> SSE for non floating-point applications.  While looking at a bug
> the other week, I caught it doing exactly that with a bit of
> kernel code.

Then you are simply using a "different" definition of "floating point 
register"
then factual on the architecture at hand.

> If you're not either turning off sse, or saving and restoring all
> sse state on entry to the kernel, then you risk data corruption.

And you are 100% sure the cost of this will be higher then constraining 
the
compiler to a defective API? If the compiler is going to use them for 
purposes
not associated necessarily with floating point calculations you will 
find yourself in
a situation where most of the user space will ask you indirectly to 
save those
registers on stack anyway... So what? You will soon give the trick of 
lazy
floating point register file saving on context switch factually up and 
pay the
penalty of a constrained register file anyway.