Groups > linux.kernel > #1209054

Re: [GIT PULL] x86 fixes

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [GIT PULL] x86 fixes
Date	2015-08-18 08:00 +0200
Message-ID	<pYI6d-5Co-1@gated-at.bofh.it> (permalink)
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I used a very old userspace, and embedded systems are much more likely to use uclibc than glibc.  However, if they try to use SSE without checking they will break on a hell of a lot more hardware.

On August 17, 2015 5:19:10 PM PDT, Andy Lutomirski <luto@amacapital.net> wrote:
>On Mon, Aug 17, 2015 at 5:06 PM, H. Peter Anvin <hpa@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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Thread

[GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-14 09:20 +0200
  Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-14 20:30 +0200
    Re: [GIT PULL] x86 fixes Andy Lutomirski <luto@amacapital.net> - 2015-08-14 20:50 +0200
      Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-14 21:00 +0200
        Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-14 21:10 +0200
          Re: [GIT PULL] x86 fixes Andy Lutomirski <luto@amacapital.net> - 2015-08-14 21:20 +0200
            Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-14 21:40 +0200
        Re: [GIT PULL] x86 fixes Andy Lutomirski <luto@amacapital.net> - 2015-08-14 21:20 +0200
    Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-17 10:10 +0200
      Re: [GIT PULL] x86 fixes Denys Vlasenko <dvlasenk@redhat.com> - 2015-08-17 13:00 +0200
        Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-17 19:00 +0200
          Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-18 10:00 +0200
      Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-17 18:50 +0200
        Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-17 19:00 +0200
          Re: [GIT PULL] x86 fixes Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-17 19:20 +0200
            Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-18 00:20 +0200
              Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-19 08:00 +0200
                Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-19 08:20 +0200
                Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-19 09:00 +0200
                Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-19 12:10 +0200
            Re: [GIT PULL] x86 fixes Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2015-08-18 01:50 +0200
      Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-17 23:10 +0200
      Re: [GIT PULL] x86 fixes Andy Lutomirski <luto@amacapital.net> - 2015-08-18 02:00 +0200
        Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-18 02:10 +0200
        Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-18 02:10 +0200
          Re: [GIT PULL] x86 fixes Andy Lutomirski <luto@amacapital.net> - 2015-08-18 02:20 +0200
            Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-18 08:00 +0200
            Re: [GIT PULL] x86 fixes "H. Peter Anvin" <hpa@zytor.com> - 2015-08-18 08:10 +0200
        Re: [GIT PULL] x86 fixes Ingo Molnar <mingo@kernel.org> - 2015-08-18 10:00 +0200

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