Home | History | Annotate | Line # | Download | only in libbacktrace
sort.c revision 1.1.1.2 
      1 /* sort.c -- Sort without allocating memory
      2    Copyright (C) 2012-2024 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 }
    109