Re: EP9312, Maverick Crunch fixes

[Paul Brook <paul at codesourcery dot com>]

On Wednesday 25 February 2004 3:28 pm, Richard Earnshaw wrote:
> > 	Hi Nick,
> >
> > In binutils-2.14/gas/config/tc-arm.c line 10227 says:
> >
> > 	if (cpu_variant & ARM_CEXT_MAVERICK)
> >
> > At some point this has been (same file, line 11718) changed to:
> >
> > 	if (cpu_variant & FPU_ARCH_MAVERICK)
> >
> > In the first case when you invoke gas with "-mcpu=ep9312" it'll add
> > "Maverick float format" flag to the resulting .o file.  In the latter it
> > won't.

I suspect I made those changes.

> > Since ep9312 does have Maverick Crunch coprocessor i would think passing
> > "-mcpu=ep9312" should be sufficient to set this flag.  The good effect is
> > that running gcc with this switch will end up generating an object file
> > with "Maverick float format".
> >
> > I wonder if we should change the code to:
> >
> > 	if (cpu_variant & (FPU_ARCH_MAVERICK | ARM_CEXT_MAVERICK))
> >
> > This way both "-mcpu=ep9312" and "-Wa,-mfpu=maverick" (from gcc
> > point of view) will do the same thing.  However, i am not sure if this
> > will break some gas/gcc convention(s) i don't know about.

It already does. -mcpu=9312 defaults to FPU_ARCH_MAVERICK, and sets the 
correspinding flags in the object file.

> I need to think through this case carefully before I reach a final
> conclusion, but my initial reaction is no, I don't think so.
>
> The reason for trying to split up the floating point from the cpu option
> is that -mcpu must not change the ABI used by the compiler (it can change
> the instructions available to use, but not the layout of data).
> Regrettably, because the FPA uses a different floating point word order
> from the VFP and Maverick the -mfpu option must have some effect on the
> ABI, hence the split.  Consider the case where Linux (or some other OS is
> being used on the ep9312 -- it should still use the same ABI as other ARM
> boards so that you can take a generic ARM/<some-os> application and run it
> on your machine.

I agree.

Paul