Undefined Reference to weak functions (Static Library + GCC)

Question

Hello everybody. First, I would like to introduce my problem to you all!

I am using Atollic TrueStudio to develop an Embedded System. In this system, I have a driver layer (built as a static library. This library contains basically the STM32 HAL, and this library contains A LOT of weak functions). These library is being compiled with ARM GCC and works great. I can link it in other projects and it does work as it should.

The second part is the problem, because I want to implement Unit Testing in the project!

For this, I have created another configuration for the same Driver Layer static library (the one with STM32 HAL code), but this time I'm compiling it with MinGW. The compilation works, but when I Try to link this library into another project (an executable project). The Linker returns "undefined reference to ..." (Image below).

PS: The problem is with the Linker, since the project finds where the weak function is declared. It can not find where it's defined though!

Edit

This is the main code

#include <MbedOS/platform/mbed_error.h>

int main(void)
{
   error("Stream obj failure, errno=%d\r\n",

   return 0;
}

This is where the function is defined (inside the static library) mbed_error.c

#include <MbedOS/platform/mbed_error.h>

static uint8_t error_in_progress = 0;

WEAK void error(const char* format,
                ...)
{

   // Prevent recursion if error is called again
   if (error_in_progress)
   {
      return;
   }

   error_in_progress = 1;

   #ifndef NDEBUG
      va_list arg;
      va_start(arg,
               format);
      mbed_error_vfprintf(format,
                          arg);
      va_end(arg);
   #endif

   exit(1);
}

This is mbed_error.h file

#ifdef __cplusplus
extern "C"
{
#endif
void error(const char* format,
           ...);

#ifdef __cplusplus
}
#endif

And this is the result from the console

13:45:44 **** Build of configuration Debug for project testeLINKER ****
make all 
gcc -o "testeLINKER.elf"  ./src/main.o   -lSTM32F7_Driver_Layer -L"E:\TrueStudio_Projects\STM32F7_Driver_Layer\Projeto\TrueStudio\UnitTestLibrary"
./src/main.o: In function `main':
E:\TrueStudio_Projects\testeLINKER\Debug/../src/main.c:33: undefined reference to `error'
collect2.exe: error: ld returned 1 exit status
make: *** [testeLINKER.elf] Error 1

13:45:44 Build Finished (took 460ms)

Edit 2 The nm output for the static library follows (just one of the files with a weak function)

    C:\Program Files (x86)\Atollic\TrueSTUDIO for STM32 9.0.0\PCTools\bin>nm E:\TrueStudio_Projects\STM32F7_Driver_Layer\Projeto\TrueStudio\UnitTestLibrary\Source\MbedOS\platform\mbed_error.o
00000000 b .bss
00000000 d .data
00000000 N .debug_abbrev
00000000 N .debug_aranges
00000000 N .debug_info
00000000 N .debug_line
00000000 r .eh_frame
00000000 r .rdata$zzz
00000000 t .text
00000000 T .weak._error.
         w _error
00000000 b _error_in_progress
         U _exit
         U _mbed_error_vfprintf

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LeoWPereira LeoWPereira · Accepted Answer · 2018-05-08T20:40:16

For everyone that may have the same doubt as I had. Here's the answer.

The problem is that PE32 file format does not support weak linkage.

Undefined Reference to weak functions (Static Library + GCC)

1 Answers