glibc/debug/backtrace.c

/* Return backtrace of current program state.
   Copyright (C) 2003-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   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 <execinfo.h>
#include <stdlib.h>
#include <unwind.h>
#include <unwind-link.h>

struct trace_arg
{
  void **array;
  struct unwind_link *unwind_link;
  _Unwind_Word cfa;
  int cnt;
  int size;
};

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_LINK_PTR (arg->unwind_link, _Unwind_GetIP) (ctx);
      if (arg->cnt > 0)
	arg->array[arg->cnt]
	  = unwind_arch_adjustment (arg->array[arg->cnt - 1],
				    arg->array[arg->cnt]);

      /* Check whether we make any progress.  */
      _Unwind_Word cfa
	= UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);

      if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
	 && cfa == arg->cfa)
       return _URC_END_OF_STACK;
      arg->cfa = cfa;
    }
  if (++arg->cnt == arg->size)
    return _URC_END_OF_STACK;
  return _URC_NO_REASON;
}

int
__backtrace (void **array, int size)
{
  struct trace_arg arg =
    {
     .array = array,
     .unwind_link = __libc_unwind_link_get (),
     .cfa = 0,
     .size = size,
     .cnt = -1
    };

  if (size <= 0 || arg.unwind_link == NULL)
    return 0;

  UNWIND_LINK_PTR (arg.unwind_link, _Unwind_Backtrace)
    (backtrace_helper, &arg);

  /* _Unwind_Backtrace seems to put NULL address above
     _start.  Fix it up here.  */
  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)