debug/backtrace.c

   1 /* Return backtrace of current program state.
   2    Copyright (C) 2003-2020 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
   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, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <libc-lock.h>
  21 #include <dlfcn.h>
  22 #include <execinfo.h>
  23 #include <gnu/lib-names.h>
  24 #include <stdlib.h>
  25 #include <unwind.h>
  26 #include <unwind-arch.h>
  27
  28 struct trace_arg
  29 {
  30   void **array;
  31   _Unwind_Word cfa;
  32   int cnt;
  33   int size;
  34 };
  35
  36 #ifdef SHARED
  37 static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
  38 static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
  39 static _Unwind_Word (*unwind_getcfa) (struct _Unwind_Context *);
  40 static void *libgcc_handle;
  41
  42
  43 /* Dummy version in case libgcc_s does not contain the real code.  */
  44 static _Unwind_Word
  45 dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
  46 {
  47   return 0;
  48 }
  49
  50
  51 static void
  52 init (void)
  53 {
  54   libgcc_handle = __libc_dlopen (LIBGCC_S_SO);
  55
  56   if (libgcc_handle == NULL)
  57     return;
  58
  59   unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
  60   unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
  61   if (unwind_getip == NULL)
  62     unwind_backtrace = NULL;
  63   unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
  64                   ?: dummy_getcfa);
  65 }
  66 #else
  67 # define unwind_backtrace _Unwind_Backtrace
  68 # define unwind_getip _Unwind_GetIP
  69 # define unwind_getcfa _Unwind_GetCFA
  70 #endif
  71
  72 static _Unwind_Reason_Code
  73 backtrace_helper (struct _Unwind_Context *ctx, void *a)
  74 {
  75   struct trace_arg *arg = a;
  76
  77   /* We are first called with address in the __backtrace function.
  78      Skip it.  */
  79   if (arg->cnt != -1)
  80     {
  81       arg->array[arg->cnt] = (void *) unwind_getip (ctx);
  82       if (arg->cnt > 0)
  83         arg->array[arg->cnt]
  84           = unwind_arch_adjustment (arg->array[arg->cnt - 1],
  85                                     arg->array[arg->cnt]);
  86
  87       /* Check whether we make any progress.  */
  88       _Unwind_Word cfa = unwind_getcfa (ctx);
  89
  90       if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
  91          && cfa == arg->cfa)
  92        return _URC_END_OF_STACK;
  93       arg->cfa = cfa;
  94     }
  95   if (++arg->cnt == arg->size)
  96     return _URC_END_OF_STACK;
  97   return _URC_NO_REASON;
  98 }
  99
 100 int
 101 __backtrace (void **array, int size)
 102 {
 103   struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
 104
 105   if (size <= 0)
 106     return 0;
 107
 108 #ifdef SHARED
 109   __libc_once_define (static, once);
 110
 111   __libc_once (once, init);
 112   if (unwind_backtrace == NULL)
 113     return 0;
 114 #endif
 115
 116   unwind_backtrace (backtrace_helper, &arg);
 117
 118   /* _Unwind_Backtrace seems to put NULL address above
 119      _start.  Fix it up here.  */
 120   if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
 121     --arg.cnt;
 122   return arg.cnt != -1 ? arg.cnt : 0;
 123 }
 124 weak_alias (__backtrace, backtrace)
 125 libc_hidden_def (__backtrace)
 126
 127
 128 #ifdef SHARED
 129 /* Free all resources if necessary.  */
 130 libc_freeres_fn (free_mem)
 131 {
 132   unwind_backtrace = NULL;
 133   if (libgcc_handle != NULL)
 134     {
 135       __libc_dlclose (libgcc_handle);
 136       libgcc_handle = NULL;
 137     }
 138 }
 139 #endif