Re: [Qemu-devel] [Patch] target-ppc mtcrf instruction not recognized

[Pierre d'Herbemont]

On 16 mai 05, at 09:54, Benjamin Herrenschmidt wrote:

> > OK, I did put this in my working repository and I'll submit this to
> > Fabrice.
> > Please try to do this change to check if other bits need to be relax 
> > or
> > not:
> >
> > Index: target-ppc/translate.c
> > ===================================================================
> > RCS file: /cvsroot/qemu/qemu/target-ppc/translate.c,v
> > retrieving revision 1.31
> > diff -u -r1.31 translate.c
> > --- target-ppc/translate.c      12 May 2005 18:46:11 -0000      1.31
> > +++ target-ppc/translate.c      14 May 2005 17:14:35 -0000
> > @@ -2123,7 +2123,7 @@
> >  }
> >
> >  /* mtcrf */
> > -GEN_HANDLER(mtcrf, 0x1F, 0x10, 0x04, 0x00100801, PPC_MISC)
> > +GEN_HANDLER(mtcrf, 0x1F, 0x10, 0x04, 0x00000801, PPC_MISC)
> >  {
> >      gen_op_load_gpr_T0(rS(ctx->opcode));
> >      gen_op_store_cr(CRM(ctx->opcode));

I've tested it: it works fine as expected.

> > And maybe someone should fill an Apple bug report to tell them their 
> > as
> > is buggy ;-)
>
> It is definitely a bug in Apple assembler I would say, so I suggest you
> add a comment in the above patch in order to avoid somebody later on
> "fixing" your mask :)

I thought it was, but it seems to be not so buggy ;)

I have had a look at the Apple's as source code of Darwin 8.0 (10.4) 
[1] and I have found an interesting comment :
            /*
             * If this is the mtcrf opcode (0x7c000120) and val is not zero and
             * has exactly one bit set then use the new form of the mtcrf
             * opcode.  This has bit 0x00100000 set and the FXM field is a bit
             * mask. Else use the old form without bit 0x00100000 set.
              */

I don't know what they are refering to, but that may have been 
introduced by the PowerPC 970 or an other new PPC, since it was not 
present on the Mac OS X 10.2's as [2].

Pierre.

 [1] http://darwinsource.opendarwin.org/10.4/cctools-576/as/ppc.c
 [2] http://darwinsource.opendarwin.org/10.2/cctools-435/as/ppc.c