Re: [Qemu-ppc] [PATCH 7/7] target/ppc: Use non-arithmetic conversions for fp load/store

[Mark Cave-Ayland]

On 05/07/18 17:48, Richard Henderson wrote:

> On 07/05/2018 09:31 AM, Programmingkid wrote:
> > > On Jul 3, 2018, at 11:17 AM, Richard Henderson <address@hidden> wrote:
> > >
> > > Memory operations have no side effects on fp state.
> > > The use of a "real" conversions between float64 and float32
> > > would raise exceptions for SNaN and out-of-range inputs.
> >
> > Would you have any documentation that tells us about converting
> > between 64 bit and 32 bit floating points?
>
> Spelled out right at the beginning of sections 4.6 (load) and 4.7 (store) of
> Book 1 of the Power ISA manual (version 3.0B) [0].
>
> I've double-checked vs RISU[1] testing of LFS and STFS, with master traces
> generated on Power 8 ppc64le, so I don't see anything immediately wrong with
> the patch.  But I haven't had time to look further than that.

I've had a quick look at this with the attached patch to compare the 
helper results before your patch and after, writing any differences to 
the console.

With this patch applied to ppc-for-3.1 I've booted MacOS 9 and recorded 
the output below:


$ ./qemu-system-ppc -cdrom MacOS921-macsbug.iso -boot d -M mac99

helper_todouble diff for arg: 3f800000  d.ll: 3ff0000000000000  ret: 
3bf0000000000000
helper_todouble diff for arg: 3f800000  d.ll: 3ff0000000000000  ret: 
3bf0000000000000

(note: MacOS 9 will hang here unless the line marked "Uncommenting this 
allows MacOS to run" in my patch is enabled)

helper_todouble diff for arg: 3f000000  d.ll: 3fe0000000000000  ret: 
3be0000000000000
helper_todouble diff for arg: 3f000000  d.ll: 3fe0000000000000  ret: 
3be0000000000000
helper_todouble diff for arg: 3f800000  d.ll: 3ff0000000000000  ret: 
3bf0000000000000
helper_todouble diff for arg: 3f800000  d.ll: 3ff0000000000000  ret: 
3bf0000000000000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_todouble diff for arg: be61b08a  d.ll: bfcc361140000000  ret: 
bbcc361140000000
helper_todouble diff for arg: 3fdf81a5  d.ll: 3ffbf034a0000000  ret: 
3bfbf034a0000000
helper_todouble diff for arg: bf402647  d.ll: bfe804c8e0000000  ret: 
bbe804c8e0000000
helper_todouble diff for arg: 3e61b08a  d.ll: 3fcc361140000000  ret: 
3bcc361140000000
helper_tosingle diff for arg: bfcc361140000000  f.l: be61b08a  ret: 9e61b08a
helper_todouble diff for arg: 3f0ccccd  d.ll: 3fe19999a0000000  ret: 
3be19999a0000000
helper_tosingle diff for arg: 3ffbf034a0000000  f.l: 3fdf81a5  ret: 1fdf81a5
helper_tosingle diff for arg: bfe804c8e0000000  f.l: bf402647  ret: 9f402647
helper_tosingle diff for arg: 3fcc361140000000  f.l: 3e61b08a  ret: 1e61b08a
helper_tosingle diff for arg: 3fe19999a0000000  f.l: 3f0ccccd  ret: 1f0ccccd
helper_todouble diff for arg: 3b800000  d.ll: 3f70000000000000  ret: 
3b70000000000000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_todouble diff for arg: 3b800000  d.ll: 3f70000000000000  ret: 
3b70000000000000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000
helper_tosingle diff for arg: 3ff0000000000000  f.l: 3f800000  ret: 1f800000


It looks like the differences are related to a flag or flags in the MSB 
byte of ret.


ATB,

Mark.

qemu-ppc-fp-helper-compare.patch
Description: Text Data