Crash under sparc/rtems-4.11 when compiling with FPU
Athanasios.Tsiodras at esa.int
Athanasios.Tsiodras at esa.int
Mon Feb 8 12:25:04 UTC 2016
Hi Jiri.
My understanding from reading the "Disaster Strikes" section of the FPU
page
(https://devel.rtems.org/wiki/TBR/UserManual/Floating_Point_Support) is
that
at some point the leon3.cfg was switched to "-msoft-float" to avoid
spurious generation
of FPU instructions in the kernel by GCC.
But as you can see in my original bug report, this ends up meaning that we
can't use
the native FPU **at all** - attempting to compile application code
*without* -msoft-float
leads to the crash in newlib that I reported.
My report includes all the steps needed to reproduce the issue - do you
see anything
wrong in the set of commands I used to build RSB or RTEMS or the sample?
Your latest answer seems to imply that if I remove the "-msoft-float" from
leon3.cfg, then
I can't, in fact use the Leon3 BSP. If that is the case, then how can I
build a native-FPU-using
version of anything?
Thanks in advance and 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: "Jiri Gaisler" <jiri at gaisler.se>
To: Athanasios.Tsiodras at esa.int, "RTEMS List" <users at rtems.org>
Date: 08/02/2016 13:07
Subject: Re: Crash under sparc/rtems-4.11 when compiling with FPU
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> 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.
Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
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