Blame debug/backtrace.c

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/* Return backtrace of current program state.
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   Copyright (C) 2003-2018 Free Software Foundation, Inc.
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   This file is part of the GNU C Library.
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   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
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   The GNU C Library is free software; you can redistribute it and/or
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   modify it under the terms of the GNU Lesser General Public
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   License as published by the Free Software Foundation; either
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   version 2.1 of the License, or (at your option) any later version.
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   The GNU C Library is distributed in the hope that it will be useful,
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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   Lesser General Public License for more details.
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   You should have received a copy of the GNU Lesser General Public
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   License along with the GNU C Library; if not, see
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   <http://www.gnu.org/licenses/>.  */
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#include <libc-lock.h>
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#include <dlfcn.h>
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#include <execinfo.h>
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#include <gnu/lib-names.h>
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#include <stdlib.h>
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#include <unwind.h>
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struct trace_arg
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{
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  void **array;
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  _Unwind_Word cfa;
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  int cnt;
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  int size;
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};
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#ifdef SHARED
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static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
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static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
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static _Unwind_Word (*unwind_getcfa) (struct _Unwind_Context *);
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static void *libgcc_handle;
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/* Dummy version in case libgcc_s does not contain the real code.  */
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static _Unwind_Word
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dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
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{
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  return 0;
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}
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static void
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init (void)
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{
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  libgcc_handle = __libc_dlopen (LIBGCC_S_SO);
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  if (libgcc_handle == NULL)
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    return;
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  unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
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  unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
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  if (unwind_getip == NULL)
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    unwind_backtrace = NULL;
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  unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
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		  ?: dummy_getcfa);
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}
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#else
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# define unwind_backtrace _Unwind_Backtrace
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# define unwind_getip _Unwind_GetIP
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# define unwind_getcfa _Unwind_GetCFA
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#endif
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static _Unwind_Reason_Code
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backtrace_helper (struct _Unwind_Context *ctx, void *a)
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{
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  struct trace_arg *arg = a;
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  /* We are first called with address in the __backtrace function.
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     Skip it.  */
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  if (arg->cnt != -1)
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    {
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      arg->array[arg->cnt] = (void *) unwind_getip (ctx);
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      /* Check whether we make any progress.  */
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      _Unwind_Word cfa = unwind_getcfa (ctx);
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      if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
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	 && cfa == arg->cfa)
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       return _URC_END_OF_STACK;
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      arg->cfa = cfa;
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    }
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  if (++arg->cnt == arg->size)
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    return _URC_END_OF_STACK;
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  return _URC_NO_REASON;
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}
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int
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__backtrace (void **array, int size)
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{
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  struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
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  if (size <= 0)
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    return 0;
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#ifdef SHARED
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  __libc_once_define (static, once);
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  __libc_once (once, init);
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  if (unwind_backtrace == NULL)
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    return 0;
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#endif
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  unwind_backtrace (backtrace_helper, &arg;;
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  /* _Unwind_Backtrace seems to put NULL address above
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     _start.  Fix it up here.  */
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  if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
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    --arg.cnt;
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  return arg.cnt != -1 ? arg.cnt : 0;
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}
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weak_alias (__backtrace, backtrace)
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libc_hidden_def (__backtrace)
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#ifdef SHARED
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/* Free all resources if necessary.  */
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libc_freeres_fn (free_mem)
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{
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  unwind_backtrace = NULL;
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  if (libgcc_handle != NULL)
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    {
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      __libc_dlclose (libgcc_handle);
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      libgcc_handle = NULL;
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    }
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}
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#endif