1 /* -*- buffer-read-only: t -*- vi: set ro: */ 2 /* DO NOT EDIT! GENERATED AUTOMATICALLY! */ 3 /* Safe automatic memory allocation. 4 Copyright (C) 2003, 2006-2007, 2009-2010 Free Software Foundation, Inc. 5 Written by Bruno Haible <bruno@clisp.org>, 2003. 6 7 This program is free software; you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 3, or (at your option) 10 any later version. 11 12 This program is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with this program; if not, write to the Free Software Foundation, 19 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 20 21 #include <config.h> 22 23 /* Specification. */ 24 #include "malloca.h" 25 26 /* Use the system functions, not the gnulib overrides in this file. */ 27 #undef malloc 28 29 /* The speed critical point in this file is freea() applied to an alloca() 30 result: it must be fast, to match the speed of alloca(). The speed of 31 mmalloca() and freea() in the other case are not critical, because they 32 are only invoked for big memory sizes. */ 33 34 #if HAVE_ALLOCA 35 36 /* Store the mmalloca() results in a hash table. This is needed to reliably 37 distinguish a mmalloca() result and an alloca() result. 38 39 Although it is possible that the same pointer is returned by alloca() and 40 by mmalloca() at different times in the same application, it does not lead 41 to a bug in freea(), because: 42 - Before a pointer returned by alloca() can point into malloc()ed memory, 43 the function must return, and once this has happened the programmer must 44 not call freea() on it anyway. 45 - Before a pointer returned by mmalloca() can point into the stack, it 46 must be freed. The only function that can free it is freea(), and 47 when freea() frees it, it also removes it from the hash table. */ 48 49 #define MAGIC_NUMBER 0x1415fb4a 50 #define MAGIC_SIZE sizeof (int) 51 /* This is how the header info would look like without any alignment 52 considerations. */ 53 struct preliminary_header { void *next; char room[MAGIC_SIZE]; }; 54 /* But the header's size must be a multiple of sa_alignment_max. */ 55 #define HEADER_SIZE \ 56 (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max) 57 struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; }; 58 /* Verify that HEADER_SIZE == sizeof (struct header). */ 59 typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1]; 60 /* We make the hash table quite big, so that during lookups the probability 61 of empty hash buckets is quite high. There is no need to make the hash 62 table resizable, because when the hash table gets filled so much that the 63 lookup becomes slow, it means that the application has memory leaks. */ 64 #define HASH_TABLE_SIZE 257 65 static void * mmalloca_results[HASH_TABLE_SIZE]; 66 67 #endif 68 69 void * 70 mmalloca (size_t n) 71 { 72 #if HAVE_ALLOCA 73 /* Allocate one more word, that serves as an indicator for malloc()ed 74 memory, so that freea() of an alloca() result is fast. */ 75 size_t nplus = n + HEADER_SIZE; 76 77 if (nplus >= n) 78 { 79 char *p = (char *) malloc (nplus); 80 81 if (p != NULL) 82 { 83 size_t slot; 84 85 p += HEADER_SIZE; 86 87 /* Put a magic number into the indicator word. */ 88 ((int *) p)[-1] = MAGIC_NUMBER; 89 90 /* Enter p into the hash table. */ 91 slot = (unsigned long) p % HASH_TABLE_SIZE; 92 ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot]; 93 mmalloca_results[slot] = p; 94 95 return p; 96 } 97 } 98 /* Out of memory. */ 99 return NULL; 100 #else 101 # if !MALLOC_0_IS_NONNULL 102 if (n == 0) 103 n = 1; 104 # endif 105 return malloc (n); 106 #endif 107 } 108 109 #if HAVE_ALLOCA 110 void 111 freea (void *p) 112 { 113 /* mmalloca() may have returned NULL. */ 114 if (p != NULL) 115 { 116 /* Attempt to quickly distinguish the mmalloca() result - which has 117 a magic indicator word - and the alloca() result - which has an 118 uninitialized indicator word. It is for this test that sa_increment 119 additional bytes are allocated in the alloca() case. */ 120 if (((int *) p)[-1] == MAGIC_NUMBER) 121 { 122 /* Looks like a mmalloca() result. To see whether it really is one, 123 perform a lookup in the hash table. */ 124 size_t slot = (unsigned long) p % HASH_TABLE_SIZE; 125 void **chain = &mmalloca_results[slot]; 126 for (; *chain != NULL;) 127 { 128 if (*chain == p) 129 { 130 /* Found it. Remove it from the hash table and free it. */ 131 char *p_begin = (char *) p - HEADER_SIZE; 132 *chain = ((struct header *) p_begin)->next; 133 free (p_begin); 134 return; 135 } 136 chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next; 137 } 138 } 139 /* At this point, we know it was not a mmalloca() result. */ 140 } 141 } 142 #endif 143