Linker error: undefined reference to `_sbrk'

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1

I get the following error when trying to use sprintf():

~/.platformio/packages/toolchain-gccarmnoneeabi@1.70201.0/bin/../lib/gcc/arm-none-eabi/7.2.1/../../../../arm-none-eabi/lib/thumb/v7-m\libc.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\genericSTM32F103VE\firmware.elf] Error 1

I have opened an issue on GitHub and you can find more details here: GitHub issue #606
I know that developers are super busy and currently it is a hard time. Thus I post here to see if anyone has encountered the same problem and solved it. Thanks!

2

It looks like you’ve downgraded the used framework to baremetal and then readded the STM32Cube files? Why not directly framework = stm32cube and then don’t include the HAL files in the project? See e.g. here.

The sprintf(adc2DecStr, "%ld", adc2Value); you do apparently wants to allocate heap memory (?) and therefore needs _sbrk as a dependency of malloc().

STM32CubeMX generated projects comewith a syscalls.c file that implement this primitive, referencing a special linkerscript place:

#include <sys/stat.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#include <time.h>
#include <sys/time.h>
#include <sys/times.h>

caddr_t _sbrk(int incr)
{
	extern char end asm("end");
	static char *heap_end;
	char *prev_heap_end;

	if (heap_end == 0)
		heap_end = &end;

	prev_heap_end = heap_end;
	if (heap_end + incr > stack_ptr)
	{
//		write(1, "Heap and stack collision\n", 25);
//		abort();
		errno = ENOMEM;
		return (caddr_t) -1;
	}

	heap_end += incr;

	return (caddr_t) prev_heap_end;
}

this works due to the auto-generated linker script having a user heap stack section with the provided end symbol

  /* User_heap_stack section, used to check that there is enough RAM left */
  ._user_heap_stack :
  {
    . = ALIGN(8);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(8);
  } >RAM

Alternatively, try to add in newlib-nano via this extra script

that you reference via

extra_scripts = add_newlibnano.py

in the platformio.ini.

2 Likes
4

I tried this just now and it worked like a charm. Thank you so much!

The reason why I don’t use the provided framework is because I followed some tutorials on personal blogs. I was totally a newbie to embedded system few weeks ago, those tutorials worked fine so I stick with them.

Definitely I will take a look at all the links you provided. Also I will learn the “official” or “recommend” way to use Platformio together with CubeMX. If I can figure these out, I will close the issue on Github later.

Thank you again!

5

There are also automated conversion tools: GitHub - ussserrr/stm32pio: Automate managing of STM32CubeMX + PlatformIO projects.

But really all that does it copy the files to the places where PlatformIO expects them. The needed folder structure is PlatformIO-standardized, as e.g. linked in the all the example projects platform-ststm32/examples at master · platformio/platform-ststm32 · GitHub.