Re: [Qemu-devel] [PATCH v3 00/15] target-sparc improvements

[Richard Henderson]

On 10/31/2016 10:21 AM, Artyom Tarasenko wrote:
> On Mon, Oct 31, 2016 at 5:06 PM, Richard Henderson <address@hidden> wrote:
> > On 10/31/2016 09:40 AM, Artyom Tarasenko wrote:
> > > >   * The "Remove asi helper code handled inline" patch retains the code
> > > > within
> > > >     ldda to handle asis that must be handled out of line.  This fixes the
> > > >     FreeBSD 10.3 boot problem.  While the UA2007 spec (and thus sun4v?)
> > > > doesn't
> > > >     allow for such, it would seem that US2 hardware does.
> > >
> > >
> > > What ASI was failing? It may still be a part of sun4v CPUs if it's
> > > described in UST1/UST2 supplements.
> >
> >
> > 0x00000000c08e5680:  clr  %g4
> > 0x00000000c08e5684:  mov  1, %g1
> > 0x00000000c08e5688:  sllx  %g1, 0x24, %o5
> > 0x00000000c08e568c:  mov  -1, %g1
> > 0x00000000c08e5690:  sllx  %g1, 0x23, %g1
> > 0x00000000c08e5694:  xor  %g1, -128, %o4
> > 0x00000000c08e5698:  ldda  [ %g4 ] #ASI_IC_TAG, %g0     ****
> > 0x00000000c08e569c:  mov  %g1, %g2
> > 0x00000000c08e56a0:  and  %g1, %o5, %g1
> > 0x00000000c08e56a4:  brz,a   %g1, 0xc08e56dc
> >
> > So indeed it would appear that FreeBSD does in fact want the half of the
> > result that would get stored into %g1.  As far as I can see they could have
> > achieved the same result with
> >
> >         ldxa    [%g4] #ASI_IC_TAG, %g1
> >         srl     %g1, 0, %g1
> >
> > to stay within the nominal spec.
>
> While your code is indeed more readable, I think the current code is
> still within the spec:
>
>  UA2005 chap 7.59:
> "Note: Execution of an LDTWA instruction with rd = 0 modifies only
> R[1]."

What I mean is found in the description of LDTWA (looking at ua2011 here):

  # Nontranslating ASIs (see page 395) should only be accessed
  # using LDXA (not LDTWA) instructions. If an LDTWA
  # referencing a nontranslating ASI is executed, per the above
  # table, it generates a DAE_invalid_asi exception
  # (impl. dep. #300-U4-Cs10).

ASI_IC_TAG is certainly nontranslating ASI.

All of the translating ASIs supported by LDTXA are already handled by 
GET_ASI_DTWINX; all of the translating ASIs supported by LDTWA are already 
handled by GET_ASI_DIRECT.  By that reading the "default:" case should simply 
raise DAE_invalid_asi.


r~