1  /* sort.c -- Sort without allocating memory
       2     Copyright (C) 2012-2023 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  }