Subject: Re: [PATCH 27/27] KVM: PPC: Add Documentation about PV interface

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sun, 04 Jul 2010 08:42:36 +1000

On Fri, 2010-07-02 at 20:41 +0200, Alexander Graf wrote:
> The u64s are 64-bit aligned, should they always be?
> 
> That's obvious, isn't it? And the ABI only specifies u64s to be 32 bit
> aligned, no? At least that's what ld and std specify.

No, the PowerPC ABI specifies u64's to be 64-bit aligned, even for
32-bit binaries.

Ben.

> > 
> >> +The "ld" and "std" instructions are transormed to "lwz" and "stw"
> instructions
> >> +respectively on 32 bit systems with an added offset of 4 to
> accomodate for big
> >> +endianness.
> > 
> > Will this add never overflow?  Is there anything that checks for it?
> 
> It basically means that to access dar, we either do
> 
> ld  rX, DAR(0)
> 
> or
> 
> lwz rX, DAR+4(0)
> 
> 
> > 
> >> +mtmsrd      rX, 0           b       <special mtmsr section>
> >> +mtmsr                       b       <special mtmsr section>
> > 
> > mtmsr rX
> 
> Nod.