I should make it clear: I was using a 486SX model in Qemu. On August 17, 2015 5:19:10 PM PDT, Andy Lutomirski <l...@amacapital.net> wrote: >On Mon, Aug 17, 2015 at 5:06 PM, H. Peter Anvin <h...@zytor.com> wrote: >> User space does not need to treat for FPU instructions, except for >performance reasons, because the kernel emulates the full x87 FPU. So >it is localized to the kernel. > >But user space needs to avoid SSE2 and such, I suspect. In general, >I'd be surprised if things work well if we emulate the FPU (and set >CR0.em? I haven't checked out Linux's FPU emulation works) if user >code sees fancy instruction sets exposed and possibly even OSXSAVE. > >None of this matters except for testing, since it's very unlikely that >any CPU exists that supports XSAVE, XMM, SSE2, etc but uses emulated >x87. But if we emulate such a beast, things could break, and I bet >that's what Ingo's seeing. (Also, lots of distros target "i686" these >days, and that might cause its own set of problems.) > >--Andy
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