glibc/debug/backtracesyms.c

/* Return list with names for address in backtrace.
   Copyright (C) 1998-2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

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

#include <ldsodefs.h>

#if __ELF_NATIVE_CLASS == 32
# define WORD_WIDTH 8
#else
/* We assume 64bits.  */
# define WORD_WIDTH 16
#endif


char **
__backtrace_symbols (void *const *array, int size)
{
  Dl_info info[size];
  int status[size];
  int cnt;
  size_t total = 0;
  char **result;

  /* Fill in the information we can get from `dladdr'.  */
  for (cnt = 0; cnt < size; ++cnt)
    {
      struct link_map *map;
      status[cnt] = _dl_addr (array[cnt], &info[cnt], &map, NULL);
      if (status[cnt] && info[cnt].dli_fname && info[cnt].dli_fname[0] != '\0')
	{
	  /* We have some info, compute the length of the string which will be
	     "<file-name>(<sym-name>+offset) [address].  */
	  total += (strlen (info[cnt].dli_fname ?: "")
		    + strlen (info[cnt].dli_sname ?: "")
		    + 3 + WORD_WIDTH + 3 + WORD_WIDTH + 5);

	  /* The load bias is more useful to the user than the load
	     address.  The use of these addresses is to calculate an
	     address in the ELF file, so its prelinked bias is not
	     something we want to subtract out.  */
	  info[cnt].dli_fbase = (void *) map->l_addr;
	}
      else
	total += 5 + WORD_WIDTH;
    }

  /* Allocate memory for the result.  */
  result = (char **) malloc (size * sizeof (char *) + total);
  if (result != NULL)
    {
      char *last = (char *) (result + size);

      for (cnt = 0; cnt < size; ++cnt)
	{
	  result[cnt] = last;

	  if (status[cnt]
	      && info[cnt].dli_fname != NULL && info[cnt].dli_fname[0] != '\0')
	    {
	      if (info[cnt].dli_sname == NULL)
		/* We found no symbol name to use, so describe it as
		   relative to the file.  */
		info[cnt].dli_saddr = info[cnt].dli_fbase;

	      if (info[cnt].dli_sname == NULL && info[cnt].dli_saddr == 0)
		last += 1 + sprintf (last, "%s(%s) [%p]",
				     info[cnt].dli_fname ?: "",
				     info[cnt].dli_sname ?: "",
				     array[cnt]);
	      else
		{
		  char sign;
		  ptrdiff_t offset;
		  if (array[cnt] >= (void *) info[cnt].dli_saddr)
		    {
		      sign = '+';
		      offset = array[cnt] - info[cnt].dli_saddr;
		    }
		  else
		    {
		      sign = '-';
		      offset = info[cnt].dli_saddr - array[cnt];
		    }

		  last += 1 + sprintf (last, "%s(%s%c%#tx) [%p]",
				       info[cnt].dli_fname ?: "",
				       info[cnt].dli_sname ?: "",
				       sign, offset, array[cnt]);
		}
	    }
	  else
	    last += 1 + sprintf (last, "[%p]", array[cnt]);
	}
      assert (last <= (char *) result + size * sizeof (char *) + total);
    }

  return result;
}
weak_alias (__backtrace_symbols, backtrace_symbols)