backtrace.c

/* Return backtrace of current program state.
   Copyright (C) 2008, 2009 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Kazu Hirata <kazu@codesourcery.com>, 2008.

   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
   <http://www.gnu.org/licenses/>.  */

#include <bits/libc-lock.h>
#include <dlfcn.h>
#include <execinfo.h>
#include <stdlib.h>
#include <unwind.h>

struct trace_arg
{
  void **array;
  int cnt, size;
};

#ifdef SHARED
static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
static _Unwind_VRS_Result (*unwind_vrs_get) (_Unwind_Context *,
					     _Unwind_VRS_RegClass,
					     _uw,
					     _Unwind_VRS_DataRepresentation,
					     void *);

static void *libgcc_handle;

static void
init (void)
{
  libgcc_handle = __libc_dlopen ("libgcc_s.so.1");

  if (libgcc_handle == NULL)
    return;

  unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
  unwind_vrs_get = __libc_dlsym (libgcc_handle, "_Unwind_VRS_Get");
  if (unwind_vrs_get == NULL)
    unwind_backtrace = NULL;
}

/* This function is identical to "_Unwind_GetGR", except that it uses
   "unwind_vrs_get" instead of "_Unwind_VRS_Get".  */
static inline _Unwind_Word
unwind_getgr (_Unwind_Context *context, int regno)
{
  _uw val;
  unwind_vrs_get (context, _UVRSC_CORE, regno, _UVRSD_UINT32, &val);
  return val;
}

/* This macro is identical to the _Unwind_GetIP macro, except that it
   uses "unwind_getgr" instead of "_Unwind_GetGR".  */
# define unwind_getip(context) \
  (unwind_getgr (context, 15) & ~(_Unwind_Word)1)
#else
# define unwind_backtrace _Unwind_Backtrace
# define unwind_getip _Unwind_GetIP
#endif

static _Unwind_Reason_Code
backtrace_helper (struct _Unwind_Context *ctx, void *a)
{
  struct trace_arg *arg = a;

  /* We are first called with address in the __backtrace function.
     Skip it.  */
  if (arg->cnt != -1)
    arg->array[arg->cnt] = (void *) unwind_getip (ctx);
  if (++arg->cnt == arg->size)
    return _URC_END_OF_STACK;
  return _URC_NO_REASON;
}

int
__backtrace (array, size)
     void **array;
     int size;
{
  struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
#ifdef SHARED
  __libc_once_define (static, once);

  __libc_once (once, init);
  if (unwind_backtrace == NULL)
    return 0;
#endif

  if (size >= 1)
    unwind_backtrace (backtrace_helper, &arg);

  if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
    --arg.cnt;
  return arg.cnt != -1 ? arg.cnt : 0;
}
weak_alias (__backtrace, backtrace)
libc_hidden_def (__backtrace)


#ifdef SHARED
/* Free all resources if necessary.  */
libc_freeres_fn (free_mem)
{
  unwind_backtrace = NULL;
  if (libgcc_handle != NULL)
    {
      __libc_dlclose (libgcc_handle);
      libgcc_handle = NULL;
    }
}
#endif