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Re: toolchain for powerpc e500v2

On Mon, Feb 7, 2011 at 3:29 AM, David Brown <> wrote:
> On 07/02/2011 12:14, Titus von Boxberg wrote:
>> Am Mo, 7.02.2011, 11:16 schrieb David Brown:
>>> On 06/02/2011 12:48, Titus von Boxberg wrote:
>>>> Hi all,
>>>> I'm trying to use ct-ng (of approx. May 2010) to generate
>>>> cross gcc-4.5.1, glibc-2.9/linux for a powerpc e500v2 / SPE.
>>>> Setting floating point to "hardware" results in a build
>>>> error in glibc where the assembler complains while compiling
>>>> an FP file about an unmatched constraint
>>>> (I could try to get the original message if it helps).
>>>> The tool chain gets built when I set floating point support to
>>>> "software".
>>>> However, the resulting compiler does not emit hardware FP instructions
>>>> unless I give -mhard-float on the command line.
>>>> Is my assumption correct that setting floating point to "hardware" turns
>>>> on
>>>> code generation for the standard PowerPC FPU which this target lacks?
>>>> I'd like to avoid having a compiler which needs target specific flags
>>>> on the command line, thus:
>>>> Does anyone know which options to turn on to get a compiler that
>>>> emits correct SPE FP instructions without explicitly being told so
>>>> by -mhard-float?
>>>> Regards
>>>> Titus
>>> If you try to use
>>> -mhard-float, either as a command-line switch or by default in the
>>> build, things are going to go badly wrong, as it will generate PPC
>>> floating point instructions that are not implemented on the e500v2.
>> That's wrong. The compiler configured for Soft FP / SPE generates the
>> correct
>> instructions (but only with -mhard-float), and the code is working as
>> well.
>> The tool chain build for hard fp indeed goes wrong. That's my problem.
> OK, if you say so - I haven't tried building from source, and it was
> something like a year and a half ago that I tried the CodeSourcery toolchain
> for the e500. ÂIt could well be that SPE floating point was activated
> slightly differently then, and has since then been better integrated as a
> variant of hardware floating point.


I use the e500v2 toolchain all the time. Please provide more info
about the build problem your having and what distribution/version you
are building on.

I am also hoping to have an e500mc (32 and 64-bit) toolchain samples soon.

>>> I would look at the CodeSourcery toolchain. ÂThey have support for SPE
>>> floating point in current releases, which you can get as source or
>>> pre-build binary. ÂI don't know whether this support has made it into
>>> the mainline FSF trees as yet (call me lazy, but I've just used the
>>> binaries from CodeSourcery), but if not then I'm sure it will
>>> eventually. ÂIt requires particular flags to enable the SPE floating
>>> point - it may be possible to build your own version that uses it by
>>> default.
>> Thanks for the hint!
>>> Remember that the SPE only supports single-precision floating point - be
>>> very careful to avoid doubles in your code (or use flags to force 32-bit
>>> "doubles"). ÂIt's easy to write "x = y * 1.5" instead of "x = y * 1.5f",
>>> and give your cpu a great deal more work.
>> This SPE supports double. I think it is enabled by -mfloat-gprs=double
>> (or maybe also by default by the compiler configuration option
>> --enable-e500_double,
>> but I did not verify this yet).
> Looking more carefully, I see you are correct. ÂI have only used the e500v1
> core, which has only single-precision floating point SPE support.
> mvh.,
> David

There are some bugs with double precision in gcc in 4.4.6, and 4.5.3.
Fixes originally went to trunk. The first two have been backported to
4.4 and 4.5, but the last one is fixed only in trunk:

... Just a heads up.

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