Crash under sparc/rtems-4.11 when compiling with FPU

Mon Feb 8 10:46:57 UTC 2016

Hi Jerry.

Thanks for the suggestion - indeed, If you look at my response to Jiri, 
you'll see that I verified that the -mhard-float is not necessary (objdump 
verified that FPU instructions are emitted by default, if you don't pass 
-msoft-float).

I am now scripting my nightly build to do the patch explicitly, so I can 
follow the tip of 4.11 with native FPU support (our intended target).

I didn't try the switch to v8 - since the removal of -msoft-float from 
leon3.cfg proved enough in my tests, and I am guessing the default 
leon3.cfg configuration was chosen to be -mcypress for a reason... At 
least I hope so :-)

Thanks!

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:   "Needell, Jerry" <Jerry.Needell at unh.edu>
To:     "Athanasios.Tsiodras at esa.int" <Athanasios.Tsiodras at esa.int>
Cc:     "Needell, Jerry" <Jerry.Needell at unh.edu>, "RTEMS List" 
<users at rtems.org>
Date:   08/02/2016 11:36
Subject:        Re: Crash under sparc/rtems-4.11 when compiling with FPU

sorry for the typo - I meant -mcpu v8 ? 
I have used this for bsps (RTEMS 4.9) with FPU without needing the 
-mhard-float specification
For non FPU bsps I have used -msoft-float
both with-mcpu v8

On Feb 8, 2016, at 5:14 AM, Needell, Jerry <Jerry.Needell at unh.edu> wrote:

I thought it was best to use -mv8 rather tahtn -mcypress for leon3 bsps? 
Does this make any difference in your case?
On Feb 8, 2016, at 4:50 AM, Athanasios.Tsiodras at esa.int wrote:

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 | MailScanner has detected a possible fraud 
attempt from "x-msg:" claiming to be 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.

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