ARM Cortex-M3 (Stellaris LM3S811) soft float problem (GCC/QEMU)

Good day,
I'm running GCC 4.4.2 (newlib 1.17) cross compiled for target:
arm-none-eabi under Linux.
I'm testing my small application under QEMU: qemu-system-arm -M lm3s811evb
and
use Eclipse/GDB to debug the application.

I've run into a problem where floating point arithmetic causes the chip to
crash. GCC was compiled with the "soft-float" option. My application is
also compiled with the "soft float" option and linked against the math
library (-lm).

The piece of offending code is:
     fTmp += 3.0;
The disassembly is:
     d24:       6b38            ldr     r0, [r7, #48] 
     d26:       492a            ldr     r1, [pc, #168]
     d28:       f000 ec32       blx     1590 <__addsf3>
     d2c:       4603            mov     r3, r0
     d2e:       633b            str     r3, [r7, #48]
Eclipse opens the file: ieee754-sf.S and focus on Line 68:
     ARM_FUNC_START addsf3

Will there be any specific reason why this helper function may cause the
chip to crash? 
Could it be a case of QEMU not simulating the ARM behavior properly?

Any help will be much appreciated
Regards,
Frikkie Thirion	   
					
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frikkiethirion <frixmail@gmail.com> wrote:
> Eclipse opens the file: ieee754-sf.S and focus on Line 68:
>     ARM_FUNC_START addsf3
> Will there be any specific reason why this helper function may cause the
> chip to crash? 

The Cortex-M3 supports only the Thumb-2 instruction set, calling an ARM
function will cause an Usage Fault. I'm guessing there's a compiler/linker
flag missing in your setup, or some bug in newlib's build process.

-a

>frikkiethirion <frixmail@gmail.com> wrote:
>> Eclipse opens the file: ieee754-sf.S and focus on Line 68:
>>     ARM_FUNC_START addsf3
>> Will there be any specific reason why this helper function may cause
the
>> chip to crash? 
>
>The Cortex-M3 supports only the Thumb-2 instruction set, calling an ARM
>function will cause an Usage Fault. I'm guessing there's a
compiler/linker
>flag missing in your setup, or some bug in newlib's build process.
>
>-a
>
>

I'm having a similar problem on LM3S9B92-EK. I'm using GNU Arm toolkit
configured with the '--with-float=soft' option. The project is compiled
with -mthumb (Thumb-2), -msoft-float (Software floating point emulation),
-mcpu=cortex-m3 (Cortex-M3 architecture) and a few other flags. I'm linking
it against libdriver and libgcc (the one that's installed into the thumb
subdirectory).

Mine crashes (HardFault) on a simple comparison of 2 floats:
float a = 1.2f;
float b = 1.1f;

UARTprintf ("\nLess %d..\n", (a < b));

And I'm pretty sure that the UART printout is working correctly..

Well, I doubt it's newlib - I could be wrong, but I guess that libgcc
should contain software floating point emulation code.

I'm a bit doubtful in the linker script that I wrote, because none of the
supplied scripts linked without errors. Another suspicion would be the
startup_gcc.c file, which I haven't modified much (due to the lack of
working float sample code). Or, it could actually be a bug in the libgcc..

. Tried to keep a long post short =P.

All suggestions are welcome,
Thank You

	   
					
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>>frikkiethirion <frixmail@gmail.com> wrote:
>>> Eclipse opens the file: ieee754-sf.S and focus on Line 68:
>>>     ARM_FUNC_START addsf3
>>> Will there be any specific reason why this helper function may cause
>the
>>> chip to crash? 
>>
>>The Cortex-M3 supports only the Thumb-2 instruction set, calling an ARM
>>function will cause an Usage Fault. I'm guessing there's a
>compiler/linker
>>flag missing in your setup, or some bug in newlib's build process.
>>
>>-a
>>
>>
>
>I'm having a similar problem on LM3S9B92-EK. I'm using GNU Arm toolkit
>configured with the '--with-float=soft' option. The project is compiled
>with -mthumb (Thumb-2), -msoft-float (Software floating point emulation),
>-mcpu=cortex-m3 (Cortex-M3 architecture) and a few other flags. I'm
linking
>it against libdriver and libgcc (the one that's installed into the thumb
>subdirectory).
>
>Mine crashes (HardFault) on a simple comparison of 2 floats:
>float a = 1.2f;
>float b = 1.1f;
>
>UARTprintf ("\nLess %d..\n", (a < b));
>
>And I'm pretty sure that the UART printout is working correctly..
>
>Well, I doubt it's newlib - I could be wrong, but I guess that libgcc
>should contain software floating point emulation code.
>
>I'm a bit doubtful in the linker script that I wrote, because none of the
>supplied scripts linked without errors. Another suspicion would be the
>startup_gcc.c file, which I haven't modified much (due to the lack of
>working float sample code). Or, it could actually be a bug in the
libgcc..
>
>. Tried to keep a long post short =P.
>
>All suggestions are welcome,
>Thank You
>
>	   
>					
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>Posted through http://www.EmbeddedRelated.com
>

Well, as it turned out, libgcc had been configured wrong (for ARM7TDMI). I
had to configure gcc with this:

--target=${GCC_TARGET} --prefix=${ARMTOOLS} --enable-interwork
--enable-multilib --enable-languages="c,c++" --with-newlib
--with-headers=../../src/newlib-${NEWLIB_VERSION}/newlib/libc/include
--with-float=soft --with-cpu=cortex-m3 --with-tune=cortex-m3
--with-mode=thumb --disable-libssp

where

NEWLIB_VERSION=1.18.0
GCC_TARGET=arm-none-eabi

and

ARMTOOLS=/usr/local/arm

Hope this helps..	   
					
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