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Re: [GIT PULL] x86 fixes

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On Fri, Aug 14, 2015 at 11:46 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>
> I think it's only slightly broken.
>
> This bit:
>
>         if ((FPU_CS & 4) != 4) {    /* Must be in the LDT */
>             /* Can only handle segmented addressing via the LDT
>                for now, and it must be 16 bit */
>             printk("FPU emulator: Unsupported addressing mode\n");
>             math_abort(FPU_info, SIGILL);
>         }
>
>         code_descriptor = FPU_get_ldt_descriptor(FPU_CS);
>
> is buggy, but no buggier than the old code.

That code seems fine to me (and explicitly errors out when it's not in
the LDT). FPU_CS is actually the CS selector value.

So testing that for being in the LDT by checking bit #2, and then
using FPU_get_ldt_descriptor() on it actually seems *correct*.

It's the actual instruction data segment handling that looks entirely
broken, and was explicitly made *more* broken by that commit.

The FPU emulation code has two different kinds of segment defines:

 - the PREFIX_xx_ defines are the segment register numbers (well,
prefix numbers)

 - the FPU_CS/SS/DS defines are the current selector values for those.

and yes, it's confusing how it tends to use the variable name
"segment" for the prefix number, when in the rest of the kernel we
tend to always track the selector value.

                 Linus
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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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