sysdeps/i386/backtrace.c

   1 /* Return backtrace of current program state.
   2    Copyright (C) 1998-2023 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <execinfo.h>
  20 #include <stdlib.h>
  21 #include <unwind-link.h>
  22
  23 struct trace_arg
  24 {
  25   void **array;
  26   struct unwind_link *unwind_link;
  27   int cnt, size;
  28   void *lastebp, *lastesp;
  29 };
  30
  31 static _Unwind_Reason_Code
  32 backtrace_helper (struct _Unwind_Context *ctx, void *a)
  33 {
  34   struct trace_arg *arg = a;
  35
  36   /* We are first called with address in the __backtrace function.
  37      Skip it.  */
  38   if (arg->cnt != -1)
  39     arg->array[arg->cnt]
  40       = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetIP) (ctx);
  41   if (++arg->cnt == arg->size)
  42     return _URC_END_OF_STACK;
  43
  44   /* %ebp is DWARF2 register 5 on IA-32.  */
  45   arg->lastebp
  46     = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetGR) (ctx, 5);
  47   arg->lastesp
  48     = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);
  49   return _URC_NO_REASON;
  50 }
  51
  52
  53 /* This is a global variable set at program start time.  It marks the
  54    highest used stack address.  */
  55 extern void *__libc_stack_end;
  56
  57
  58 /* This is the stack layout we see with every stack frame
  59    if not compiled without frame pointer.
  60
  61             +-----------------+        +-----------------+
  62     %ebp -> | %ebp last frame--------> | %ebp last frame--->...
  63             |                 |        |                 |
  64             | return address  |        | return address  |
  65             +-----------------+        +-----------------+
  66
  67    First try as far to get as far as possible using
  68    _Unwind_Backtrace which handles -fomit-frame-pointer
  69    as well, but requires .eh_frame info.  Then fall back to
  70    walking the stack manually.  */
  71
  72 struct layout
  73 {
  74   struct layout *ebp;
  75   void *ret;
  76 };
  77
  78
  79 int
  80 __backtrace (void **array, int size)
  81 {
  82   struct trace_arg arg =
  83     {
  84      .array = array,
  85      .unwind_link = __libc_unwind_link_get (),
  86      .size = size,
  87      .cnt = -1,
  88     };
  89
  90   if (size <= 0 || arg.unwind_link == NULL)
  91     return 0;
  92
  93   UNWIND_LINK_PTR (arg.unwind_link, _Unwind_Backtrace)
  94     (backtrace_helper, &arg);
  95
  96   if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
  97     --arg.cnt;
  98   else if (arg.cnt < size)
  99     {
 100       struct layout *ebp = (struct layout *) arg.lastebp;
 101
 102       while (arg.cnt < size)
 103         {
 104           /* Check for out of range.  */
 105           if ((void *) ebp < arg.lastesp || (void *) ebp > __libc_stack_end
 106               || ((long) ebp & 3))
 107             break;
 108
 109           array[arg.cnt++] = ebp->ret;
 110           ebp = ebp->ebp;
 111         }
 112     }
 113   return arg.cnt != -1 ? arg.cnt : 0;
 114 }
 115 weak_alias (__backtrace, backtrace)
 116 libc_hidden_def (__backtrace)