ppc 405 floating point math emulation

ppc 405 floating point math emulation

[Steven Mueller]

Hello,

I'm interested in building a kernel with math emulation enabled for an
embedded IBM ppc 405.  (It'd be nice to allow customers to run ppc
apps on our cards without having to recompile them with soft float
support.)  When I try this with an old Monta Vista kernel from April
12th (used in an a HardHat pre-release, but no longer available), the
compile eventually fails while linking and mentions some 8xx specific
symbols.  I assume this is leftovers from 2 years ago when there
appear to have been efforts to add math emulation support for the 8xx
chips?  Anyway, make says the following and stops:

make[2]: Leaving directory `/home/dank/ixia/Software/kernel-ppc/arch/ppc/math-emu'
make[1]: Leaving directory `/home/dank/ixia/Software/kernel-ppc/arch/ppc/math-emu'
/usr/local/ppc-old/bin/powerpc-linux-ld -T arch/ppc/vmlinux.lds -Ttext 0xc0000000 -Bstatic arch/ppc/kernel/head_4xx.o init/main.o init/version.o \
        --start-group \
        arch/ppc/kernel/kernel.o arch/ppc/mm/mm.o arch/ppc/lib/lib.o kernel/kernel.o mm/mm.o fs/fs.o ipc/ipc.o arch/ppc/math-emu/math-emu.o \
        drivers/block/block.o drivers/char/char.o drivers/misc/misc.o drivers/net/net.o drivers/media/media.o  \
        net/network.o \
        /home/dank/ixia/Software/kernel-ppc/lib/lib.a \
        --end-group \
        -o vmlinux
arch/ppc/kernel/kernel.o: In function `Soft_emulate_8xx':
/home/dank/ixia/Software/kernel-ppc/arch/ppc/kernel/softemu8xx.c:129: undefined reference to `print_8xx_pte'
/home/dank/ixia/Software/kernel-ppc/arch/ppc/kernel/softemu8xx.c:129: relocation truncated to fit: R_PPC_REL24 print_8xx_pte
/home/dank/ixia/Software/kernel-ppc/arch/ppc/kernel/softemu8xx.c:130: undefined reference to `get_8xx_pte'

If anyone has already developed a solution for this, would you please
consider posting the patch?  Thank you!

Steve

--
Steven Mueller
diffusor@ugcs.caltech.edu

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Re: ppc 405 floating point math emulation

[Dan Malek]

Steven Mueller wrote:

> ..... When I try this with an old Monta Vista kernel from April
> 12th (used in an a HardHat pre-release, but no longer available), the
> compile eventually fails while linking and mentions some 8xx specific
> symbols.

The MontaVista kernel, tools, libraries and applications are all created
as a cohesive distribution.  In the case of processors that don't have
floating point hardware, everything is created to use the in-line software
floating point.  You can't mix tools, libraries, and applications with
different floating point implementations within the same distribution.

Since the kernel never had to support floating point emulation, the 4xx
processors never had a proper kernel emulation interface for that.  This
was recently changed in the public source trees, which is what you should
be using if you want this feature.

> .....  I assume this is leftovers from 2 years ago when there
> appear to have been efforts to add math emulation support for the 8xx
> chips?

No, it is just that the 8xx was the only PowerPC that ever supported
the kernel floating point emulation traps, so when you select that option
it tries to hook into 8xx functions that don't exist when 8xx isn't configured.


Thanks.


	-- Dan


** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/

Re: ppc 405 floating point math emulation

[Kenneth Johansson]

Steven Mueller wrote:
>
> Hello,
>
> I'm interested in building a kernel with math emulation enabled for an
> embedded IBM ppc 405.  (It'd be nice to allow customers to run ppc
> apps on our cards without having to recompile them with soft float
> support.)

Yes it's nice. I'am running a full debian testing installation over nfsroot
on my cards.

> If anyone has already developed a solution for this, would you please
> consider posting the patch?  Thank you!

Just remove the printing or uppgrade to the devel tree it could use some more
testing.

--
Kenneth Johansson
Ericsson Business Innovation AB   Tel: +46 8 404 71 83
Viderögatan 3                     Fax: +46 8 404 72 72
164 80 Stockholm                  kenneth.johansson@inn.ericsson.se

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