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98399780 | 1 | /* Safe automatic memory allocation. |
4a626d0a | 2 | Copyright (C) 2003, 2006-2007, 2009-2015 Free Software Foundation, Inc. |
98399780 YQ |
3 | Written by Bruno Haible <bruno@clisp.org>, 2003. |
4 | ||
5 | This program is free software; you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 3, or (at your option) | |
8 | any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
16 | along with this program; if not, see <http://www.gnu.org/licenses/>. */ | |
17 | ||
18 | #define _GL_USE_STDLIB_ALLOC 1 | |
19 | #include <config.h> | |
20 | ||
21 | /* Specification. */ | |
22 | #include "malloca.h" | |
23 | ||
24 | #include <stdint.h> | |
25 | ||
26 | #include "verify.h" | |
27 | ||
28 | /* The speed critical point in this file is freea() applied to an alloca() | |
29 | result: it must be fast, to match the speed of alloca(). The speed of | |
30 | mmalloca() and freea() in the other case are not critical, because they | |
31 | are only invoked for big memory sizes. */ | |
32 | ||
33 | #if HAVE_ALLOCA | |
34 | ||
35 | /* Store the mmalloca() results in a hash table. This is needed to reliably | |
36 | distinguish a mmalloca() result and an alloca() result. | |
37 | ||
38 | Although it is possible that the same pointer is returned by alloca() and | |
39 | by mmalloca() at different times in the same application, it does not lead | |
40 | to a bug in freea(), because: | |
41 | - Before a pointer returned by alloca() can point into malloc()ed memory, | |
42 | the function must return, and once this has happened the programmer must | |
43 | not call freea() on it anyway. | |
44 | - Before a pointer returned by mmalloca() can point into the stack, it | |
45 | must be freed. The only function that can free it is freea(), and | |
46 | when freea() frees it, it also removes it from the hash table. */ | |
47 | ||
48 | #define MAGIC_NUMBER 0x1415fb4a | |
49 | #define MAGIC_SIZE sizeof (int) | |
50 | /* This is how the header info would look like without any alignment | |
51 | considerations. */ | |
4a626d0a | 52 | struct preliminary_header { void *next; int magic; }; |
98399780 YQ |
53 | /* But the header's size must be a multiple of sa_alignment_max. */ |
54 | #define HEADER_SIZE \ | |
55 | (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max) | |
4a626d0a PA |
56 | union header { |
57 | void *next; | |
58 | struct { | |
59 | char room[HEADER_SIZE - MAGIC_SIZE]; | |
60 | int word; | |
61 | } magic; | |
62 | }; | |
63 | verify (HEADER_SIZE == sizeof (union header)); | |
98399780 YQ |
64 | /* We make the hash table quite big, so that during lookups the probability |
65 | of empty hash buckets is quite high. There is no need to make the hash | |
66 | table resizable, because when the hash table gets filled so much that the | |
67 | lookup becomes slow, it means that the application has memory leaks. */ | |
68 | #define HASH_TABLE_SIZE 257 | |
69 | static void * mmalloca_results[HASH_TABLE_SIZE]; | |
70 | ||
71 | #endif | |
72 | ||
73 | void * | |
74 | mmalloca (size_t n) | |
75 | { | |
76 | #if HAVE_ALLOCA | |
77 | /* Allocate one more word, that serves as an indicator for malloc()ed | |
78 | memory, so that freea() of an alloca() result is fast. */ | |
79 | size_t nplus = n + HEADER_SIZE; | |
80 | ||
81 | if (nplus >= n) | |
82 | { | |
4a626d0a | 83 | void *p = malloc (nplus); |
98399780 YQ |
84 | |
85 | if (p != NULL) | |
86 | { | |
87 | size_t slot; | |
4a626d0a | 88 | union header *h = p; |
98399780 | 89 | |
4a626d0a | 90 | p = h + 1; |
98399780 YQ |
91 | |
92 | /* Put a magic number into the indicator word. */ | |
4a626d0a | 93 | h->magic.word = MAGIC_NUMBER; |
98399780 YQ |
94 | |
95 | /* Enter p into the hash table. */ | |
96 | slot = (uintptr_t) p % HASH_TABLE_SIZE; | |
4a626d0a | 97 | h->next = mmalloca_results[slot]; |
98399780 YQ |
98 | mmalloca_results[slot] = p; |
99 | ||
100 | return p; | |
101 | } | |
102 | } | |
103 | /* Out of memory. */ | |
104 | return NULL; | |
105 | #else | |
106 | # if !MALLOC_0_IS_NONNULL | |
107 | if (n == 0) | |
108 | n = 1; | |
109 | # endif | |
110 | return malloc (n); | |
111 | #endif | |
112 | } | |
113 | ||
114 | #if HAVE_ALLOCA | |
115 | void | |
116 | freea (void *p) | |
117 | { | |
118 | /* mmalloca() may have returned NULL. */ | |
119 | if (p != NULL) | |
120 | { | |
121 | /* Attempt to quickly distinguish the mmalloca() result - which has | |
122 | a magic indicator word - and the alloca() result - which has an | |
123 | uninitialized indicator word. It is for this test that sa_increment | |
124 | additional bytes are allocated in the alloca() case. */ | |
125 | if (((int *) p)[-1] == MAGIC_NUMBER) | |
126 | { | |
127 | /* Looks like a mmalloca() result. To see whether it really is one, | |
128 | perform a lookup in the hash table. */ | |
129 | size_t slot = (uintptr_t) p % HASH_TABLE_SIZE; | |
130 | void **chain = &mmalloca_results[slot]; | |
131 | for (; *chain != NULL;) | |
132 | { | |
4a626d0a | 133 | union header *h = p; |
98399780 YQ |
134 | if (*chain == p) |
135 | { | |
136 | /* Found it. Remove it from the hash table and free it. */ | |
4a626d0a PA |
137 | union header *p_begin = h - 1; |
138 | *chain = p_begin->next; | |
98399780 YQ |
139 | free (p_begin); |
140 | return; | |
141 | } | |
4a626d0a PA |
142 | h = *chain; |
143 | chain = &h[-1].next; | |
98399780 YQ |
144 | } |
145 | } | |
146 | /* At this point, we know it was not a mmalloca() result. */ | |
147 | } | |
148 | } | |
149 | #endif |