Re: [Xen-devel] [V10 PATCH 12/23] PVH xen: Support privileged op emulation for PVH

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.08.13 at 03:59, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> On Wed, 7 Aug 2013 14:49:50 +0100
> George Dunlap <dunlapg@xxxxxxxxx> wrote:
>> On Wed, Jul 24, 2013 at 2:59 AM, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> 
>> wrote:
>> > + * We need vcpu because during context switch, going from PV to
>> > PVH,
>> > + * in save_segments() current has been updated to next, and no
>> > longer pointing
>> > + * to the PV, but the intention is to get selector for the PV.
>> > Checking
>> > + * is_pvh_vcpu(current) will yield incorrect results in such a
>> > case.
>> > + */
>> > +#define read_segment_register(vcpu, regs, name)                   \
>> > +({  u16 __sel;                                                    \
>> > +    struct cpu_user_regs *_regs = (regs);                         \
>> > +                                                                  \
>> > +    if ( is_pvh_vcpu(vcpu) && guest_mode(_regs) )                 \
>> > +        __sel = pvh_get_selector(vcpu, x86_seg_##name);           \
>> > +    else                                                          \
>> > +        asm volatile ( "movw %%" #name ",%0" : "=r" (__sel) );    \
>> 
>> Is there a reason you discarded the STR() macro here?
> 
> Suggested by Jan to change it, not sure the reason. Jan do you recall?

I think this is the result of multiple iterations of the patch, where
intermediately the stringification had disappeared altogether.
When I requested it to be restored, I used the simpler # operator
in the outline.

In any event I think STR() should go away altogether (where
necessary replaced by __stringify()), and was needlessly used
in the original code here: The intended use is when you need
the argument macro expanded before stringification, which is
not the case here.

Jan


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