Question

I’m attempting to build a simple project using Yagarto and Eclipse for an ARM microcontroller platform. In my startup code, I have this (which I believe is fairly standard and uninteresting):

void Reset_Handler(void)
{
  /* Initialize data and bss */
  __Init_Data();

  /* Call CTORS of static objects */
  __libc_init_array();

  /* Call the application's entry point.*/
  main();

  while(1) { ; }
}

Unless I comment out the call to __libc_init_array(), I get the following error from the linker:

arm-none-eabi-g++ -nostartfiles -mthumb -mcpu=cortex-m4 -TC:/Users/mark/workspace/stm32_cpp_test/STM32F40x_1024k_192k_flash.ld -gc-sections -Wl,-Map=test_rom.map,--cref,--no-warn-mismatch -o stm32_cpp_test "system\\syscalls.o" "system\\startup_stm32f4xx.o" "system\\mini_cpp.o" "system\\cmsis\\system_stm32f4xx.o" main.o 
d:/utils/yagarto/bin/../lib/gcc/arm-none-eabi/4.7.2/../../../../arm-none-eabi/lib/thumb/v7m\libg.a(lib_a-init.o): In function `__libc_init_array':
C:\msys\1.0\home\yagarto\newlib-build\arm-none-eabi\thumb\v7m\newlib\libc\misc/../../../../../../../newlib-1.20.0/newlib/libc/misc/init.c:37: undefined reference to `_init'
collect2.exe: error: ld returned 1 exit status

Why am I getting this “undefined reference” error? What am I missing? I assume there’s some linker flag that I’m missing, but I can’t for the life of me figure out what.

Answer 1

I’m no expert, but:

Probably _init (the normal runtime entry point) references the code that executes the ctor and dtor tables.

You use -nostartfiles so avoid the standard startup, and probably that whole startcode is eliminated by –gc-sections. The explicit call adds a reference again.

If omitting –gc-sections doesn’t solve it, it might also be a missing keep() statement in your (embedded) linker script that keeps the entry code at all times, or your own startup code
(startup_*) should reference it