libunwind on arm

[Jesper Taxbøl]

Hi, I am relatively new to this library, but find it very nifty to print a callstack on a crash. 

I face some issues getting function names printed out on an Arm device I am working on.

First some backstory.

I am on an Arm platform (http://wiki.lindeni.org/index.php/Lindenis_V536)

The compilers I am using to crosscompile for the platform are called

arm-openwrt-linux-muslgnueabi-gcc and arm-openwrt-linux-muslgnueabi-g++

I am using libunwind in a version that is bundled with the crosscompile environment. (1.1 or 1.2.1 - both versions are available as zipfiles in the toolchain)

I can choose them and compile programs that link againgst libunwind and I am allowed to execute them on the platform.

My backtrace function is this

void backtrace() {
  unw_cursor_t cursor;
  unw_context_t context;

  // Initialize cursor to current frame for local unwinding.
  unw_getcontext(&context);
  unw_init_local(&cursor, &context);

  // Unwind frames one by one, going up the frame stack.
  while (unw_step(&cursor) > 0) {
    unw_word_t pc;
    unw_word_t offset;
    unw_get_reg(&cursor, UNW_REG_IP, &pc);
    if (pc == 0) {
      break;
    }
    printf("%010p:", (void*)pc);

    char sym[256];
    if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0) {
      printf(" (%s+0x%p)\n", sym, (void*)offset);
    } else {
      printf(" -- error: unable to obtain symbol name for this frame\n");
    }    
  }
}

I get stacktraces like this: (Always without function names)

0x00016bb0: -- error: unable to obtain symbol name for this frame
0xb6fb9fac: -- error: unable to obtain symbol name for this frame
0x00016950: -- error: unable to obtain symbol name for this frame
0x00014db4: -- error: unable to obtain symbol name for this frame
0xb6f9c4ec: -- error: unable to obtain symbol name for this frame

I have tried a range of compiler flags to change this, but with little luck.

-g -funwind-tables -unwind-tables -fomit-frame-pointer -rdynamic -fasynchronous-unwind-tables -mapcs-frame 

What could I be doing wrong? Or are function names just not accessible on ARM?

Kind regards

Jesper