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Re: Multilib support for 68040


Glynn Smith wrote:
> 
> -----Original Message-----
> From: Aaron J. Grier [mailto:aaron@frye.com]
> Sent: Tuesday, January 22, 2002 10:59 AM
> To: Glynn Smith
> Cc: crossgcc@sourceware.cygnus.com
> Subject: Re: Multilib support for 68040
> 
> On Mon, Jan 21, 2002 at 12:26:18PM -0800, Glynn Smith wrote:
> > I am using gcc 2.95.2 configured as a Cross m68k compiler hosted on
> > PPC-LINUX.  The standard multi-lib support seems to be for 68000 68020
> > 68881 & soft-float.
> 
> and cpu32 and m5200.  :)
> 
> > Question 1
> >
> > Can this version or a later version of the GCC compiler be configured
> > so that it generates a 68040 multilib branch uses only floating point
> > instruction from the set of instructions that are supported by the
> > 68040 FPCP and does NOT emulate the unsupported instructions using
> > FLINE TRAPS
> 
> according to the documentation for 2.95.2, yes:
> 
> `-m68040'
>      Generate output for a 68040.  This is the default when the
>      compiler is configured for 68040-based systems.
> Where is this default configured and how do I see what my default is?
> 
>      This option inhibits the use of 68881/68882 instructions that have
>      to be emulated by software on the 68040.  Use this option if your
>      68040 does not have code to emulate those instructions.
> How do I configure the compiler for multilib support for -m68040 so that
> libraries get built with this option?

I have cc'ed Chris Johns since this is the same thing his 68060 patches
do for that CPU.

> > Question 2
> > Motorola FPCPs have the option of setting them up so that the floating
> > point precession is embedded in each floating point instruction rather
> > that setting the precession in the FPCR (Control register) before each
> > operation.  Is there a compiler flag to enable this option?
> 
> I have no idea.  have you disassembled code to see what the compiler
> default is?

My guess would be to doubt it since there would have to be a 
way in the programming language to specify the precision for the
compiler to use.  I suppose gcc could vary it on a file by file
basis but this feels questionable.
 
> --
>   Aaron J. Grier  |   Frye Electronics, Tigard, OR   |  aaron@frye.com
>      "In a few thousand years people will be scratching their heads
>        wondering how on earth the first computer was invented and
>           bootstrapped without a prior computer to do it with."
>                     --  Chris Malcolm, on comp.arch
> 
> ------
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