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 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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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.


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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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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-float=soft --with-cpu=cortex-m3 --with-tune=cortex-m3

--with-mode=thumb --disable-libssp


NEWLIB_VERSION=1.18.0 GCC_TARGET=arm-none-eabi



Hope this helps..

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