1 /* sort.c -- Sort without allocating memory 2 Copyright (C) 2012-2018 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