Re: [Libunwind-devel] Help : Lowest address of stack frame causing segfault

[Pallav Singh]

Hi Arun,

 

Thanks for the explanation given. It’s really Useful.

 

We are trying to use libunwind to unwind function call stack, But

We need to have Both the boundary of stack frame with –O3 optimization

where frame pointers are omitted by Compilers.

 

1. Considering the below example, Can we make assumption that stack pointer

returned by API “unw_get_reg(&cursor, UNW_REG_SP, &sp)” will be always

be at 16 byte displacement to previous stack frame bottom using

show_backtrace(void) of libunwind.

 

Previous stack frame bottom = sp + 16.

 

http://stackoverflow.com/questions/7534420/gas-explanation-of-cfi-def-cfa-offset

 

2. Can we get bottom of stack frame, causing segfault using libunwind.

 

   We are only getting instruction pointer as bottom most address.

  

 

#define UNW_LOCAL_ONLY

#include <libunwind.h>

 

void show_backtrace (void) {

  unw_cursor_t cursor; unw_context_t uc;

  unw_word_t ip, sp;

 

  unw_getcontext(&uc);

  unw_init_local(&cursor, &uc);

  while (unw_step(&cursor) > 0) {

    unw_get_reg(&cursor, UNW_REG_IP, &ip);

    unw_get_reg(&cursor, UNW_REG_SP, &sp);

    printf ("ip = %lx, sp = %lx\n", (long) ip, (long) sp);

  }

}

 

PS : we are fine with tail recursion optimization of compilers.

 

Thanks

Pallav Singh