Crash under sparc/rtems-4.11 when compiling with FPU

Athanasios.Tsiodras at esa.int Athanasios.Tsiodras at esa.int
Mon Feb 8 09:57:05 UTC 2016


(slight correction - I pasted the wrong output, the binary works fine :-)

*** BEGIN OF TEST HELLO WORLD ***
Hello World, 93647.304688
*** END OF TEST HELLO WORLD ***

I am unaware of the proper etiquette for this, so I better check - am I 
allowed to edit the wiki page at 
https://devel.rtems.org/wiki/TBR/UserManual/Floating_Point_Support to add 
a section about Leon3 native FPU usage and the need for the patch I did in 
leon3.cfg?

Apologies if I am overstepping - I just don't want others to go through 
the same efforts that I did.

Kind regards,
Thanassis.

European Space Agency (via HE Space)
Thanassis Tsiodras
Real-time Embedded Software Engineer 
System, Software and Technology Department

ESTEC
Keplerlaan 1, PO Box 299
NL-2200 AG Noordwijk, The Netherlands
Athanasios.Tsiodras at esa.int | www.esa.int
T +31 71 565 5332



From:   Athanasios.Tsiodras at esa.int
To:     "RTEMS List" <users at rtems.org>
Date:   08/02/2016 10:50
Subject:        Re: Crash under sparc/rtems-4.11 when compiling with FPU
Sent by:        "users" <users-bounces at rtems.org>



I verified Sebastian's suggestion - by modifying the leon3.cfg file... 

    diff --git a/c/src/lib/libbsp/sparc/leon3/make/custom/leon3.cfg 
b/c/src/lib/libbsp/sparc/leon3/make/custom/leon3.cfg 
    index 58f2f07..30fc3a4 100644 
    --- a/c/src/lib/libbsp/sparc/leon3/make/custom/leon3.cfg 
    +++ b/c/src/lib/libbsp/sparc/leon3/make/custom/leon3.cfg 
    @@ -9,7 +9,8 @@ RTEMS_CPU_MODEL=leon3 

     #  This contains the compiler options necessary to select the CPU 
model 
     #  and (hopefully) optimize for it. 
    -CPU_CFLAGS = -mcpu=cypress -msoft-float 
    +CPU_CFLAGS = -mcpu=cypress -mhard-float 

...the generated binary of hello.exe works fine - I went a step further 
and did a test calculation, too: 

    diff --git a/testsuites/samples/hello/init.c 
b/testsuites/samples/hello/init.c 
    index d8fe450..6ee33f6 100644 
    --- a/testsuites/samples/hello/init.c 
    +++ b/testsuites/samples/hello/init.c 
    @@ -27,8 +27,13 @@ rtems_task Init( 
       rtems_task_argument ignored 
     ) 
     { 
    +  int i = 0; 
    +  float a=3.14159f, b=1.0f; 
    + 
       rtems_test_begin(); 
    -  printf( "Hello World\n" ); 
    +  for (i=0; i<10; i++) 
    +      b*=a; 
    +  printf( "Hello World, %f\n", b ); 
       rtems_test_end(); 
       exit( 0 ); 
     } 

...which worked fine: 

    (gdb) tar extended-remote ... ( to grmon) 
    (gdb) c 
    Continuing. 

    *** BEGIN OF TEST HELLO WORLD *** 
    Hello World, 1.000000 
    *** END OF TEST HELLO WORLD *** 

...and I made sure that FPU instructions are inside: 

      for (i=0; i<10; i++) 
      28:   82 80 7f ff     addcc  %g1, -1, %g1 
      2c:   12 bf ff ff     bne  28 <Init+0x28> 
      30:   91 a2 09 29     fmuls  %f8, %f9, %f8 
          b*=a; 
      printf( "Hello World, %f\n", b ); 
      34:   91 a0 19 28     fstod  %f8, %f8 

So, executive summary....  It seems that the default compilation settings 
of the Leon3 BSP forbid "real FPU" work. 
If one needs to work in native (non-emulated) FPU mode, then the leon3.cfg 
must be patched as I showed above. 

In the long run, as Sebastian indicated, a leon3fp (and a corresponding 
leon2fp, I imagine) 
should ideally be added as new BSP targets - and the FPU page 
(https://devel.rtems.org/wiki/TBR/UserManual/Floating_Point_Support) 
should probably 
be updated to indicate this. 

Thanks to everyone for their help, 
Thanassis. 


European Space Agency (via HE Space) 
Thanassis Tsiodras 
Real-time Embedded Software Engineer 
System, Software and Technology Department 

ESTEC 
Keplerlaan 1, PO Box 299 
NL-2200 AG Noordwijk, The Netherlands 
Athanasios.Tsiodras at esa.int | www.esa.int 
T +31 71 565 5332 



From:        "Sebastian Huber" <sebastian.huber at embedded-brains.de> 
To:        "RTEMS List" <users at rtems.org> 
Cc:        software at gaisler.com 
Date:        07/02/2016 07:40 
Subject:        Re: Crash under sparc/rtems-4.11 when compiling with FPU 
Sent by:        "users" <users-bounces at rtems.org> 



Hello Athanasios,

it was always a miracle to me how you are supposed to use the leon2/leon3 
BSPs with a FPU. If you want to use the FPU, then the BSP must be built 
with the -mhard-float option, otherwise the FPU support is not enabled in 
the operating system support. In addition the application configuration 
must be compiled with exactly the same compiler flags as the BSP, 
otherwise it will generate a corrupt configuration.

I think we need leon2fp and leon3fp BSPs, which use -mhard-float.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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