sysdeps/i386/backtrace.c

   1 /* Return backtrace of current program state.
   2    Copyright (C) 1998, 2000, 2003, 2004, 2005 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <bits/libc-lock.h>
  22 #include <dlfcn.h>
  23 #include <execinfo.h>
  24 #include <stdlib.h>
  25 #include <unwind.h>
  26
  27 struct trace_arg
  28 {
  29   void **array;
  30   int cnt, size;
  31   void *lastebp, *lastesp;
  32 };
  33
  34 #ifdef SHARED
  35 static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
  36 static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
  37 static _Unwind_Ptr (*unwind_getcfa) (struct _Unwind_Context *);
  38 static _Unwind_Ptr (*unwind_getgr) (struct _Unwind_Context *, int);
  39
  40 static void
  41 init (void)
  42 {
  43   void *handle = __libc_dlopen ("libgcc_s.so.1");
  44
  45   if (handle == NULL)
  46     return;
  47
  48   unwind_backtrace = __libc_dlsym (handle, "_Unwind_Backtrace");
  49   unwind_getip = __libc_dlsym (handle, "_Unwind_GetIP");
  50   unwind_getcfa = __libc_dlsym (handle, "_Unwind_GetCFA");
  51   unwind_getgr = __libc_dlsym (handle, "_Unwind_GetGR");
  52   if (unwind_getip == NULL || unwind_getgr == NULL || unwind_getcfa == NULL)
  53     unwind_backtrace = NULL;
  54 }
  55 #else
  56 # define unwind_backtrace _Unwind_Backtrace
  57 # define unwind_getip _Unwind_GetIP
  58 # define unwind_getcfa _Unwind_GetCFA
  59 # define unwind_getgr _Unwind_GetGR
  60 #endif
  61
  62 static _Unwind_Reason_Code
  63 backtrace_helper (struct _Unwind_Context *ctx, void *a)
  64 {
  65   struct trace_arg *arg = a;
  66
  67   /* We are first called with address in the __backtrace function.
  68      Skip it.  */
  69   if (arg->cnt != -1)
  70     arg->array[arg->cnt] = (void *) unwind_getip (ctx);
  71   if (++arg->cnt == arg->size)
  72     return _URC_END_OF_STACK;
  73
  74   /* %ebp is DWARF2 register 5 on IA-32.  */
  75   arg->lastebp = (void *) unwind_getgr (ctx, 5);
  76   arg->lastesp = (void *) unwind_getcfa (ctx);
  77   return _URC_NO_REASON;
  78 }
  79
  80
  81 /* This is a global variable set at program start time.  It marks the
  82    highest used stack address.  */
  83 extern void *__libc_stack_end;
  84
  85
  86 /* This is the stack layout we see with every stack frame
  87    if not compiled without frame pointer.
  88
  89             +-----------------+        +-----------------+
  90     %ebp -> | %ebp last frame--------> | %ebp last frame--->...
  91             |                 |        |                 |
  92             | return address  |        | return address  |
  93             +-----------------+        +-----------------+
  94
  95    First try as far to get as far as possible using
  96    _Unwind_Backtrace which handles -fomit-frame-pointer
  97    as well, but requires .eh_frame info.  Then fall back to
  98    walking the stack manually.  */
  99
 100 struct layout
 101 {
 102   struct layout *ebp;
 103   void *ret;
 104 };
 105
 106
 107 int
 108 __backtrace (array, size)
 109      void **array;
 110      int size;
 111 {
 112   struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
 113 #ifdef SHARED
 114   __libc_once_define (static, once);
 115
 116   __libc_once (once, init);
 117   if (unwind_backtrace == NULL)
 118     return 0;
 119 #endif
 120
 121   if (size >= 1)
 122     unwind_backtrace (backtrace_helper, &arg);
 123
 124   if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
 125     --arg.cnt;
 126   else if (arg.cnt < size)
 127     {
 128       struct layout *ebp = (struct layout *) arg.lastebp;
 129
 130       while (arg.cnt < size)
 131         {
 132           /* Check for out of range.  */
 133           if ((void *) ebp < arg.lastesp || (void *) ebp > __libc_stack_end
 134               || ((long) ebp & 3))
 135             break;
 136
 137           array[arg.cnt++] = ebp->ret;
 138           ebp = ebp->ebp;
 139         }
 140     }
 141   return arg.cnt != -1 ? arg.cnt : 0;
 142 }
 143 weak_alias (__backtrace, backtrace)
 144 libc_hidden_def (__backtrace)