libbacktrace/sort.c

   1 /* sort.c -- Sort without allocating memory
   2    Copyright (C) 2012-2017 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Google.
   4
   5 Redistribution and use in source and binary forms, with or without
   6 modification, are permitted provided that the following conditions are
   7 met:
   8
   9     (1) Redistributions of source code must retain the above copyright
  10     notice, this list of conditions and the following disclaimer.
  11
  12     (2) Redistributions in binary form must reproduce the above copyright
  13     notice, this list of conditions and the following disclaimer in
  14     the documentation and/or other materials provided with the
  15     distribution.
  16
  17     (3) The name of the author may not be used to
  18     endorse or promote products derived from this software without
  19     specific prior written permission.
  20
  21 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  22 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  23 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  24 DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
  25 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  26 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  27 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  29 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  30 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  31 POSSIBILITY OF SUCH DAMAGE.  */
  32
  33 #include "config.h"
  34
  35 #include <stddef.h>
  36 #include <sys/types.h>
  37
  38 #include "backtrace.h"
  39 #include "internal.h"
  40
  41 /* The GNU glibc version of qsort allocates memory, which we must not
  42    do if we are invoked by a signal handler.  So provide our own
  43    sort.  */
  44
  45 static void
  46 swap (char *a, char *b, size_t size)
  47 {
  48   size_t i;
  49
  50   for (i = 0; i < size; i++, a++, b++)
  51     {
  52       char t;
  53
  54       t = *a;
  55       *a = *b;
  56       *b = t;
  57     }
  58 }
  59
  60 void
  61 backtrace_qsort (void *basearg, size_t count, size_t size,
  62                  int (*compar) (const void *, const void *))
  63 {
  64   char *base = (char *) basearg;
  65   size_t i;
  66   size_t mid;
  67
  68  tail_recurse:
  69   if (count < 2)
  70     return;
  71
  72   /* The symbol table and DWARF tables, which is all we use this
  73      routine for, tend to be roughly sorted.  Pick the middle element
  74      in the array as our pivot point, so that we are more likely to
  75      cut the array in half for each recursion step.  */
  76   swap (base, base + (count / 2) * size, size);
  77
  78   mid = 0;
  79   for (i = 1; i < count; i++)
  80     {
  81       if ((*compar) (base, base + i * size) > 0)
  82         {
  83           ++mid;
  84           if (i != mid)
  85             swap (base + mid * size, base + i * size, size);
  86         }
  87     }
  88
  89   if (mid > 0)
  90     swap (base, base + mid * size, size);
  91
  92   /* Recurse with the smaller array, loop with the larger one.  That
  93      ensures that our maximum stack depth is log count.  */
  94   if (2 * mid < count)
  95     {
  96       backtrace_qsort (base, mid, size, compar);
  97       base += (mid + 1) * size;
  98       count -= mid + 1;
  99       goto tail_recurse;
 100     }
 101   else
 102     {
 103       backtrace_qsort (base + (mid + 1) * size, count - (mid + 1),
 104                        size, compar);
 105       count = mid;
 106       goto tail_recurse;
 107     }
 108 }