problem with malloc

Asked by Jens Vankeirsbilck


I'm trying to execute some C++ code on an LPC1768, an ARM Cortex-M3 driven microcontroller.
The C++ code uses malloc and free, so I included <stdlib.h>. While building and compiling the code with arm-none-eabi-gcc gave no errors, the binary does not execute. The Cortex-M3 goes into HardFault.

When compiling the exact same code with the online compiler of mbed ( the binary does execute!

This leads me to believe that my compilation process, when I use arm-none-eabi-gcc, is not correct. Could it be that the wrong <stdlib.h> and thus the wrong implementation of malloc() and free() are included into the binary, causing the hardfault?

here are the contents of the makefile:

--> dijkstra.cpp includes the code that calls malloc() and free()
$(cpp) -I(...) dijkstra.cpp -o algorithms/dijkstra.o

--> linker to create the elf (the binary is extracted from the .elf )
$(cpp) -T"lpc1768.ld" -nostartfiles -Xlinker --gc-sections -WL,-Map,"" --specs=nosys.specs ..... -o dijkstra.elf

Could you please let me know what I do wrong?

Thanks in advance.

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GNU Arm Embedded Toolchain Edit question
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Thomas Preud'homme (thomas-preudhomme) said :

Hi Jens,

malloc will rely on _sbrk to get memory so you need to implement _sbrk in your application. The mbed compiler must includes some library with such an implementation.

Best regards,


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Jens Vankeirsbilck (jens-vankeirsbilck) said :

Hi Thomas

would a missing _sbrk function not result in a failed compilation process. During my online search to solve my problem, i came across the missing _sbrk. However, in every case that resulted in a failure to compile.

As i wrote before, everything compiles fine. The binary just does not execute...

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Thomas Preud'homme (thomas-preudhomme) said :

Hi Jens,

Linking with nosys.specs will bring a default _sbrk implementation that will return memory just after the symbol end (which points at the end of the .bss segment).

Best regards.

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