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Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code |
Date: |
Thu, 6 Jan 2011 15:35:53 +0100 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Wed, Jan 05, 2011 at 11:13:06PM +0000, Stuart Brady wrote:
> On Wed, Jan 05, 2011 at 11:21:06AM +0100, Aurelien Jarno wrote:
>
> > But that's not the subject we are talking about HPPA guest support.
> > target-hppa fork still (partially) uses dyngen code, which we don't
> > support in upstream for more than *2 years*.
>
> I'd agree -- the fork is currently dead. Whilst I do plan to revive it
> at some point, I would support removal of those particular lines, as:
>
> Dead code is noise. It doesn't contribute anything, so you may as
> well remove it.
>
> It's easy enough to add it back at a later date.
>
> Dead code is buggy code. Previously, the code was quietening
> signaling NaNs incorrectly. MIPS now uses a default quiet NaN,
> but HPPA would need a different fix.
>
> It's not even clear which of the two possible fixes should be applied
> (or whether both should be applied with a means of selecting the
> behaviour at run-time). I gather that we need to clear the MSB of
> the significand, and then set its least-significant-but-one bit,
> either unconditionally, or perhaps only if the significand would
> otherwise be zero. However, I don't yet know which of those two
> behaviours is implemented by hardware, and even if only one is
> implemented, I still feel we'd still need a comment explaining that
> the architecture's specification permits the alternate behaviour.
>
> A few random thank-yous:
>
> I do really appreciate the effort to avoid removing lines that would
> only be added back at a later date -- if we had an HPPA target fork
> that was ready to be merged back in a week or two, then I'd argue that
> there's no point, but that's not the case.
>
> Thanks for the comments on sNaN quietening for HPPA. I would hopefully
> read the PA1.1 spec thoroughly enough and test on real hardware upon
> reaching the point where floating point support is somewhere higher
> up on the TODO list... :-) However, the comments can hardly hurt!
>
> What is important here is that the code be rewritten in a clean manner,
> so that there are no unnecessary obstacles to modifying SoftFloat to
> support new targets. The patches that I've seen definitely seem to
> move in that direction, so I'm quite happy. Of course, fixing those
> architectures that are already upstream is the main objective! -- and
> if this helps other forks, that can't be a bad thing.
>
> I do have a few concerns regarding SoftFloat, though:
>
> FIXMEs should be left in the code (or a document maintained on the
> Wiki) to keep track of which architectures have been considered
> (which I believe are x86, arm, mips, ppc) and which ones haven't.
> This is in reference to one particular FIXME that was removed,
> but perhaps shouldn't have been.
>
> Is there any plan to deal with use of float*_is_quiet_nan(), where
> float*_is_any_nan() was intended? These should really either be
> fixed (and tested), or if not, a FIXME should be added.
The problem with these functions is that they are used in target-*/
and not directly part of the softfloat code.
I have reviewed MIPS and PowerPC targets, they both use these functions
correctly.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, (continued)
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/04
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Andreas Färber, 2011/01/04
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/04
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Andreas Färber, 2011/01/05
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/05
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Stuart Brady, 2011/01/05
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Peter Maydell, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Stuart Brady, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Peter Maydell, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Stuart Brady, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code,
Aurelien Jarno <=
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Peter Maydell, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Peter Maydell, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Nathan Froyd, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Andreas Färber, 2011/01/06
- Re: [Qemu-devel] [PATCH 1/6] softfloat: remove HPPA specific code, Aurelien Jarno, 2011/01/06
[Qemu-devel] [PATCH 2/6] softfloat: fix float{32, 64}_maybe_silence_nan() for MIPS, Aurelien Jarno, 2011/01/03