Crash under sparc/rtems-4.11 when compiling with FPU
Jiri Gaisler
jiri at gaisler.se
Mon Feb 8 12:07:45 UTC 2016
On 08/02/16 11:46, Athanasios.Tsiodras at esa.int wrote:
> 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 :-)
Just remember that if the compiler emits *any* FPU instruction in the
kernel or non-FPU threads, you can get a crash. You should use objdump
on the final binary to verify that you don't have spurious FPU
instructions in the wrong place.
Jiri.
>
>
> 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_
> <mailto: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_
> <mailto: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_ <mailto:Athanasios.Tsiodras at esa.int>|
> *_MailScanner has detected a possible fraud attempt from "x-msg:"
> claiming to be_*___www.esa.int_ <x-msg://11/www.esa.int>
> T +31 71 565 5332
>
>
>
> From: "Sebastian Huber" <_sebastian.huber at embedded-brains.de_
> <mailto:sebastian.huber at embedded-brains.de>>
> To: "RTEMS List" <_users at rtems.org_ <mailto:users at rtems.org>>
> Cc: _software at gaisler.com_ <mailto: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_
> <mailto: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_
> <http://embedded-brains.de/>
> PGP : Public key available on request.
>
> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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