> > On Tue, Jan 4, 2011 at 22:44, Dave Hylands <[email protected]> wrote: > > That is correct. In some architectures, attempts to use floating point > > from the kernel will work. I've seen some x86 code that uses it. > > > AFAIK, once x86 didn't supported due to floating point related > registers are not correctly (or even doing?) saved and restored during > context switching. So maybe it is fixed now... > > -- >
I've often wondered about this oft-cited kernel behaviour too, in my naivety. I understand that this must be on a per-arch basis, but does this mean that the kernel doesn't police FP access at _all_ (perhaps this is what Mohit means too)? Does code like X for example have to access it directly, or does it just use the GPU? What about other user-space code - does it have a separate library and do its own security? Video drivers? Sorry if these are basic questions, I grepped for float in the kernel but as-yet the associated code looks really arcane to me - if anyone could answer any of these questions generally (if that's possible) that would be very helpful with visualizing the mechanism. Maybe I'm looking in the wrong place. When I started looking at the kernel I imagined this small, neat, concise piece of highly efficient code so I wasn't surprised there was no float (don't laugh - how one learns :-/ ) ... I suppose any float per-arch 'hacks' (to get a larger word size) would not be worth the overhead of the mode switch and extra code? Thanks Julie
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