backtrace() / backtrace_symbols() results are confusing

[Chris Markle]

All,

Confused about backtrace() and backtrace_symbols() results... In the 
following sample program which has basically main() -> dummy_func1() -> 
 dummy_func2() -> dummy_func3() -> print_trace() -> backtrace(), 
backtrace() returns 7 stack frames. I understand the last 6 which show 
libc -> main() -> f1() -> f2() -> f3() -> print_trace() -> 
backtrace()... But what is the first entry?

test1(backtrace_symbols+0x3d) [0x8048681]

When I try an addr2line on 8048681 (0x8048681) it returns "??"

I haven't even called backtrace_symbols() yet just backtrace().

Can someone shed some light on this please?

Chris

output of execution follows:

$ ./test1
obtained 7 stack frames
test1(print_trace+0x1d) [0x804877d]
test1(dummy_func3+0xb) [0x8048857]
test1(dummy_func2+0xb) [0x8048847]
test1(dummy_func1+0xb) [0x8048837]
test1(main+0xb) [0x8048823]
/lib/i686/libc.so.6(__libc_start_main+0x93) [0x4003e657]
test1(backtrace_symbols+0x3d) [0x8048681]

code follows:

/*
 * Basic test program to see how glibc backtrace() and
 * backtrace_symbols() work.
 */

#include <stdio.h>
#include <execinfo.h>
#include <stdlib.h>

void dummy_func1(void);
void dummy_func2(void);
void dummy_func3(void);

void
print_trace(void)
{
  void *array[200];
  size_t size;
  char **strings;
  size_t i;

  size = backtrace(array, 200);
  printf("obtained %zd stack frames\n", size);

  strings = backtrace_symbols(array, size);

  for (i = 0; i < size; i++)
    printf("%s\n", strings[i]);

  free(strings);
}

int
main(void)
{
  dummy_func1();
  return 0;
}

void
dummy_func1(void)
{
  dummy_func2();
}

void
dummy_func2(void)
{
  dummy_func3();
}

void
dummy_func3(void)
{
  print_trace();
}