debug/backtrace.c

   1 /* Return backtrace of current program state.
   2    Copyright (C) 2003-2019 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
  27 struct trace_arg
  28 {
  29   void **array;
  30   _Unwind_Word cfa;
  31   int cnt;
  32   int size;
  33 };
  34
  35 #ifdef SHARED
  36 static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
  37 static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
  38 static _Unwind_Word (*unwind_getcfa) (struct _Unwind_Context *);
  39 static void *libgcc_handle;
  40
  41
  42 /* Dummy version in case libgcc_s does not contain the real code.  */
  43 static _Unwind_Word
  44 dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
  45 {
  46   return 0;
  47 }
  48
  49
  50 static void
  51 init (void)
  52 {
  53   libgcc_handle = __libc_dlopen (LIBGCC_S_SO);
  54
  55   if (libgcc_handle == NULL)
  56     return;
  57
  58   unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
  59   unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
  60   if (unwind_getip == NULL)
  61     unwind_backtrace = NULL;
  62   unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
  63                   ?: dummy_getcfa);
  64 }
  65 #else
  66 # define unwind_backtrace _Unwind_Backtrace
  67 # define unwind_getip _Unwind_GetIP
  68 # define unwind_getcfa _Unwind_GetCFA
  69 #endif
  70
  71 static _Unwind_Reason_Code
  72 backtrace_helper (struct _Unwind_Context *ctx, void *a)
  73 {
  74   struct trace_arg *arg = a;
  75
  76   /* We are first called with address in the __backtrace function.
  77      Skip it.  */
  78   if (arg->cnt != -1)
  79     {
  80       arg->array[arg->cnt] = (void *) unwind_getip (ctx);
  81
  82       /* Check whether we make any progress.  */
  83       _Unwind_Word cfa = unwind_getcfa (ctx);
  84
  85       if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
  86          && cfa == arg->cfa)
  87        return _URC_END_OF_STACK;
  88       arg->cfa = cfa;
  89     }
  90   if (++arg->cnt == arg->size)
  91     return _URC_END_OF_STACK;
  92   return _URC_NO_REASON;
  93 }
  94
  95 int
  96 __backtrace (void **array, int size)
  97 {
  98   struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
  99
 100   if (size <= 0)
 101     return 0;
 102
 103 #ifdef SHARED
 104   __libc_once_define (static, once);
 105
 106   __libc_once (once, init);
 107   if (unwind_backtrace == NULL)
 108     return 0;
 109 #endif
 110
 111   unwind_backtrace (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   return arg.cnt != -1 ? arg.cnt : 0;
 118 }
 119 weak_alias (__backtrace, backtrace)
 120 libc_hidden_def (__backtrace)
 121
 122
 123 #ifdef SHARED
 124 /* Free all resources if necessary.  */
 125 libc_freeres_fn (free_mem)
 126 {
 127   unwind_backtrace = NULL;
 128   if (libgcc_handle != NULL)
 129     {
 130       __libc_dlclose (libgcc_handle);
 131       libgcc_handle = NULL;
 132     }
 133 }
 134 #endif