RE: [linuxsh-dev] Re: Floating point problem

[Bao C. H. <ba...@se...>]

It still crashed when $fpscr was set to 0x80004

(gdb) p/x $fpscr=0x80004
$2 = 0x80004
(gdb) p/x $fpscr
$3 = 0x80004
(gdb) c
Continuing.

 status=%x

 dum=%f
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> -----Original Message-----
> From: lin...@li...
> [mailto:lin...@li...]On Behalf Of
> kaz Kojima
> Sent: Thursday, August 16, 2001 5:48 PM
> To: lin...@li...
> Subject: [linuxsh-dev] Re: Floating point problem
>
>
> "Bao C. Ha" <ba...@se...> wrote:
> > (gdb) n
> > 14              printf("\n status=%x\n", (int)status);
> > (gdb) set archi sh4
> > The target architecture is assumed to be sh4
> > (gdb) p/x $fpscr
> > $2 = 0x3f737871
> > (gdb) n
> >
> >  status=%x
> >
> >  dum=%f
> > ......
> > CRASHED!!!
> >
> > So it is the wrong FPU mode.  How do we fix it?
>
> Before going ahead, please try
>   (gdb) p/x $fpscr=0x80004
>   (gdb) c
> instead of p/x $fpscr to confirm the problem. If it works,
> the problem must be caused by $fpscr. If this is the case,
> I think that the real problem is the __fpscr_values table
> in your shared libraries.
>
> The $fpscr value problem is a long standing problem. As you
> know, SH-4 FPU has no individual instructions to handle float
> and double, but a mode flags in $fpscr. So the mixture of
> the float and double arithmetic needs the wierd switching of
> $fpscr value. So, an easiest and only one easy workaround is
> to use double only :-)
>
> GCC uses __fpscr_values for this switching. This table is
> the array of 32-bit words and __fpscr_values[0] is the value
> for float and __fpscr_values[1] is for double. The switchig
> is done by the load from these values to $fpscr. There are
> versions of compiler have problems in this switching, though
> this is not the case in current problem since there is no
> problem with static linking.
> This __fpscr_values table is in libgcc.a and defined as .comm
> symbol originally. But this is not suitable for the shared
> library. The __fpscr_values table is writable to set rounding
> and floating exception mode, so it must be the unique entity.
> The Right Thing is to put it in the shared libgcc like as
> we've done it in our gcc-3.0 patch. So the 2nd workaround is
> to use gcc-3.0 + our SH patch and rebuild all libraries using
> it. But it isn't so easy and will cause another problems.
>
> 	kaz
>
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