[Buildroot] Problem with iperf

[Rex Ashbaugh <rexa@xeratech.com>]

Also, check how your cross compiler is configured for floating point
handling..

http://www.arm.linux.org.uk/mailinglists/faq.php

3. I feel really confused about what's the difference with gcc
          soft-float support and the kernel NWFPE/FastFPE support?
          [31 January 2004 - np]
          Scenario 1 (hard-float): The compiler emits opcodes designed to
          be  used  with a hardware floating point coprocessor (FPU). The
          FPU  usually  has a set of extra registers for its use, and the
          compiler  may as well pass floating point argument to functions
          through  those registers. This is of course the best performing
          solution when a real hardware FPU is used.

          Scenario  2  (soft-float): the compiler converts floating point
          operations into function calls and a special library is used to
          provide  all  functions performing the required operations, all
          in software with no FPU instructions at all. There is obviously
          no  extra  floating  point  registers  available  in this case,
          therefore  all  FP  arguments  to  functions  have to be passed
          through  standard  registers or on the stack. This is of course
          the best performing solution when no hardware FPU is available,
          given  that  the  library  implementing  the  FP  operations is
          optimally coded.

          Now,  unfortunately, the default on ARM Linux has traditionally
          been set to have the compiler use hard-float, even if ARM Linux
          never  ran  on any ARM CPU with a real hardware FPU. The CPU is
          therefore  raising  the invalid instruction exception each time
          some  FPU  opcode  is  encountered.  Then the kernel traps that
          exception,  looks  at the given FPU instruction and emulates it
          in  software.  But here not only the kernel must perform the FP
          operation,  it  must  emulates  the whole hardware FPU as well.
          That's  what  NWFPE or FastFPE are doing. This is obviously the
          worst  performing  arrangement that can be due to the exception
          trap and emulation overhead



On 2/28/08, Nicola Salvemini <nicolasalvemini@yahoo.it> wrote:
>
> Hi Rex,
>
> Yes I tried with the previous version (2.0.1) of iperf, bat I had same
> results.
> I'm waiting for a replay from iperf maintainer.
> Best regards,
>
> Nicola.
>
> ----- Messaggio originale -----
> Da: Rex Ashbaugh <rexa@xeratech.com>
> A: Nicola Salvemini <nicolasalvemini@yahoo.it>
> Cc: buildroot at uclibc.org
> Inviato: Mercoled? 27 febbraio 2008, 16:52:03
> Oggetto: Re: [Buildroot] Problem with iperf
>
>
> NWFPE is the floating point emulator.
>
> 00000002 is a floating point divide-by-zero.
>
> try another version of iperf maybe?
> report this problem to the iperf maintainer?
> -Rex
>
>
> On 2/27/08, Nicola Salvemini <nicolasalvemini@yahoo.it> wrote:
> >
> > Hi all,
> >
> > I have a ARM arm926t (it's a little-endian) target platform and I use
> > buildroot to cross-compile applications.
> > I include iperf in the package selection for the target and the build
> > phase go to the end without problems, but when I try to use iperf on the
> > target, I take an exception:
> >
> > NWFPE: iperf[770] takes exception 00000002 at c00288f0 from 400f4580
> > NWFPE: iperf[770] takes exception 00000002 at c00288f0 from 400f4580
> > NWFPE: iperf[770] takes exception 00000002 at c00288f0 from 400f4580
> >
> > Could you please give me an idea to resolve the problem?
> > Thanks in advance,
> >
> >
> > Nicola.
> >
> >
> >
> >
> >
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