1  /* Return backtrace of current program state.
       2     Copyright (C) 2013-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Library General Public License as
       7     published by the Free Software Foundation; either version 2 of the
       8     License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Library General Public License for more details.
      14  
      15     You should have received a copy of the GNU Library General Public
      16     License along with the GNU C Library; see the file COPYING.LIB.  If
      17     not, see <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <execinfo.h>
      20  #include <stddef.h>
      21  #include <sysdep.h>
      22  #include <sys/trap.h>
      23  #include <backtrace.h>
      24  #include <unwind-link.h>
      25  
      26  struct layout
      27  {
      28    unsigned long locals[8];
      29    unsigned long ins[6];
      30    unsigned long next;
      31    void *return_address;
      32  };
      33  
      34  struct trace_arg
      35  {
      36    void **array;
      37    struct unwind_link *unwind_link;
      38    _Unwind_Word cfa;
      39    int cnt;
      40    int size;
      41  };
      42  
      43  static _Unwind_Reason_Code
      44  backtrace_helper (struct _Unwind_Context *ctx, void *a)
      45  {
      46    struct trace_arg *arg = a;
      47    _Unwind_Ptr ip;
      48  
      49    /* We are first called with address in the __backtrace function.
      50       Skip it.  */
      51    if (arg->cnt != -1)
      52      {
      53        ip = UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetIP) (ctx);
      54        arg->array[arg->cnt] = (void *) ip;
      55  
      56        /* Check whether we make any progress.  */
      57        _Unwind_Word cfa
      58  	= UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);
      59  
      60        if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
      61  	 && cfa == arg->cfa)
      62         return _URC_END_OF_STACK;
      63        arg->cfa = cfa;
      64      }
      65    if (++arg->cnt == arg->size)
      66      return _URC_END_OF_STACK;
      67    return _URC_NO_REASON;
      68  }
      69  
      70  int
      71  __backtrace (void **array, int size)
      72  {
      73    int count;
      74    struct trace_arg arg =
      75      {
      76       .array = array,
      77       .unwind_link = __libc_unwind_link_get (),
      78       .size = size,
      79       .cnt = -1,
      80      };
      81  
      82    if (size <= 0)
      83      return 0;
      84  
      85    if (arg.unwind_link == NULL)
      86      {
      87        struct layout *current;
      88        unsigned long fp, i7;
      89  
      90        asm volatile ("mov %%fp, %0" : "=r"(fp));
      91        asm volatile ("mov %%i7, %0" : "=r"(i7));
      92        current = (struct layout *) (fp + BACKTRACE_STACK_BIAS);
      93  
      94        array[0] = (void *) i7;
      95  
      96        if (size == 1)
      97  	return 1;
      98  
      99        backtrace_flush_register_windows();
     100        for (count = 1; count < size; count++)
     101  	{
     102  	  array[count] = current->return_address;
     103  	  if (!current->next)
     104  	    break;
     105  	  current = (struct layout *) (current->next + BACKTRACE_STACK_BIAS);
     106  	}
     107      }
     108    else
     109      {
     110        UNWIND_LINK_PTR (arg.unwind_link, _Unwind_Backtrace)
     111  	(backtrace_helper, &arg);
     112  
     113        /* _Unwind_Backtrace seems to put NULL address above
     114  	 _start.  Fix it up here.  */
     115        if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
     116  	--arg.cnt;
     117        count = arg.cnt != -1 ? arg.cnt : 0;
     118      }
     119    return count;
     120  }
     121  weak_alias (__backtrace, backtrace)
     122  libc_hidden_def (__backtrace)