Re: [Xen-devel] [PATCH v5 3/4] VMX: use proper instruction mnemonics if assembler supports them

[Tim Deegan <tim@xxxxxxx>]

At 13:30 +0100 on 29 Aug (1377783058), Jan Beulich wrote:
> >>> On 29.08.13 at 13:47, Tim Deegan <tim@xxxxxxx> wrote:
> > At 16:31 +0100 on 26 Aug (1377534696), Jan Beulich wrote:
> >> -static inline unsigned long __vmread_safe(unsigned long field, int *error)
> >> +static inline bool_t __vmread_safe(unsigned long field, unsigned long 
> >> *value)
> >>  {
> >> -    unsigned long ecx;
> >> +    bool_t okay;
> >>  
> >> -    asm volatile ( VMREAD_OPCODE
> >> -                   MODRM_EAX_ECX
> >> -                   /* CF==1 or ZF==1 --> rc = -1 */
> >> -                   "setna %b0 ; neg %0"
> >> -                   : "=q" (*error), "=c" (ecx)
> >> -                   : "0" (0), "a" (field)
> >> +    asm volatile (
> >> +#ifdef HAVE_GAS_VMX
> >> +                   "vmread %2, %1\n\t"
> >> +#else
> >> +                   VMREAD_OPCODE MODRM_EAX_ECX
> >> +#endif
> >> +                   /* CF==1 or ZF==1 --> rc = 0 */
> >> +                   "setnbe %0"
> > 
> > This inversion of the (undocumented) return value could be a nasty
> > surprise for anyone backporting code that uses __vmread_safe().  Can you
> > please leave it as it was?
> 
> The prior return value was the value read

Sorry, I had somehow missed this.  That's enough to cause compile issues
so I guess it'll be obvious that the function has changed.  Would be
nice if the new verions had a comment to say when it returns 0 and when
1.  Either way, Reviewed-by: Tim Deegan <tim@xxxxxxx>

Cheers,

Tim.

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