sysdeps/x86_64/backtrace.c

   1 /* Return backtrace of current program state.
   2    Copyright (C) 2003-2017 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    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <libc-lock.h>
  21 #include <dlfcn.h>
  22 #include <execinfo.h>
  23 #include <stdlib.h>
  24 #include <unwind.h>
  25
  26 struct trace_arg
  27 {
  28   void **array;
  29   _Unwind_Word cfa;
  30   int cnt;
  31   int size;
  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_Word (*unwind_getcfa) (struct _Unwind_Context *);
  38 static void *libgcc_handle;
  39
  40
  41 /* Dummy version in case libgcc_s does not contain the real code.  */
  42 static _Unwind_Word
  43 dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
  44 {
  45   return 0;
  46 }
  47
  48
  49 static void
  50 init (void)
  51 {
  52   libgcc_handle = __libc_dlopen ("libgcc_s.so.1");
  53
  54   if (libgcc_handle == NULL)
  55     return;
  56
  57   unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
  58   unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
  59   if (unwind_getip == NULL)
  60     unwind_backtrace = NULL;
  61   unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
  62                   ?: dummy_getcfa);
  63 }
  64 #else
  65 # define unwind_backtrace _Unwind_Backtrace
  66 # define unwind_getip _Unwind_GetIP
  67 # define unwind_getcfa _Unwind_GetCFA
  68 #endif
  69
  70 static _Unwind_Reason_Code
  71 backtrace_helper (struct _Unwind_Context *ctx, void *a)
  72 {
  73   struct trace_arg *arg = a;
  74
  75   /* We are first called with address in the __backtrace function.
  76      Skip it.  */
  77   if (arg->cnt != -1)
  78     {
  79       arg->array[arg->cnt] = (void *) unwind_getip (ctx);
  80
  81       /* Check whether we make any progress.  */
  82       _Unwind_Word cfa = unwind_getcfa (ctx);
  83
  84       if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
  85          && cfa == arg->cfa)
  86        return _URC_END_OF_STACK;
  87       arg->cfa = cfa;
  88     }
  89   if (++arg->cnt == arg->size)
  90     return _URC_END_OF_STACK;
  91   return _URC_NO_REASON;
  92 }
  93
  94 int
  95 __backtrace (void **array, int size)
  96 {
  97   struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
  98
  99   if (size <= 0)
 100     return 0;
 101
 102 #ifdef SHARED
 103   __libc_once_define (static, once);
 104
 105   __libc_once (once, init);
 106   if (unwind_backtrace == NULL)
 107     return 0;
 108 #endif
 109
 110   unwind_backtrace (backtrace_helper, &arg);
 111
 112   /* _Unwind_Backtrace seems to put NULL address above
 113      _start.  Fix it up here.  */
 114   if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
 115     --arg.cnt;
 116   return arg.cnt != -1 ? arg.cnt : 0;
 117 }
 118 weak_alias (__backtrace, backtrace)
 119 libc_hidden_def (__backtrace)
 120
 121
 122 #ifdef SHARED
 123 /* Free all resources if necessary.  */
 124 libc_freeres_fn (free_mem)
 125 {
 126   unwind_backtrace = NULL;
 127   if (libgcc_handle != NULL)
 128     {
 129       __libc_dlclose (libgcc_handle);
 130       libgcc_handle = NULL;
 131     }
 132 }
 133 #endif