Re: [ros-dev] [ros-diffs] [dgorbachev] 53907: [NTOSKRNL] Use inline asm in KiIsNpxErrataPresent(). C code can be optimized in a wrong way.

[Alex Ionescu]

Care to explain?

If it can be optimized the wrong way -- use a pragma or fix the compiler.

I hate these kinds of patches. I think Timo would agree.

Best regards,
Alex Ionescu

On Fri, Sep 30, 2011 at 5:03 PM, [e-mail] wrote:
> Author: dgorbachev
> Date: Fri Sep 30 21:03:29 2011
> New Revision: 53907
>
> URL: http://svn.reactos.org/svn/reactos?rev=53907&view=rev
> Log:
> [NTOSKRNL]
> Use inline asm in KiIsNpxErrataPresent(). C code can be optimized in a
> wrong way.
>
> Modified:
>    trunk/reactos/ntoskrnl/ke/i386/cpu.c
>
> Modified: trunk/reactos/ntoskrnl/ke/i386/cpu.c
> URL:
> http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/ke/i386/cpu.c?rev=...
>
> ==============================================================================
> --- trunk/reactos/ntoskrnl/ke/i386/cpu.c [iso-8859-1] (original)
> +++ trunk/reactos/ntoskrnl/ke/i386/cpu.c [iso-8859-1] Fri Sep 30 21:03:29
> 2011
> @@ -1254,9 +1254,9 @@
>  INIT_FUNCTION
>  KiIsNpxErrataPresent(VOID)
>  {
> BOOLEAN ErrataPresent;
> static double Value1 = 4195835.0, Value2 = 3145727.0;
> INT ErrataPresent;
> ULONG Cr0;
>
> volatile double Value1, Value2;
>
> /* Disable interrupts */
> _disable();
>
> @@ -1269,9 +1269,30 @@
>     Ke386FnInit();
> /* Multiply the magic values and divide, we should get the result back
>
> */
> Value1 = 4195835.0;
> Value2 = 3145727.0;
> ErrataPresent = (Value1 * Value2 / 3145727.0) != 4195835.0;
>
> +#ifdef __GNUC__
> __asm__ __volatile__
> (
>    "fldl %1\n\t"
>    "fdivl %2\n\t"
>    "fmull %2\n\t"
>    "fldl %1\n\t"
>    "fsubp\n\t"
>    "fistpl %0\n\t"
>    : "=m" (ErrataPresent)
>    : "m" (Value1),
>      "m" (Value2)
> );
>
> +#else
> __asm
> {
>    fld Value1
>    fdiv Value2
>    fmul Value2
>    fld Value1
>    fsubp
>    fistp ErrataPresent
> };
>
> +#endif
> /* Restore CR0 */
> __writecr0(Cr0);
>
> @@ -1280,7 +1301,7 @@
>     _enable();
> /* Return if there's an errata */
> return ErrataPresent;
> return ErrataPresent != 0;
>
> }
>
> VOID