Commit | Line | Data |
---|---|---|
ffca4c22 AW |
1 | /* Safe automatic memory allocation. |
2 | Copyright (C) 2003, 2006-2007 Free Software Foundation, Inc. | |
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 Lesser General Public License as published by | |
7 | the Free Software Foundation; either version 2, 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 Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public License | |
16 | along with this program; if not, write to the Free Software Foundation, | |
17 | Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ | |
18 | ||
19 | #include <config.h> | |
20 | ||
21 | /* Specification. */ | |
22 | #include "malloca.h" | |
23 | ||
24 | /* The speed critical point in this file is freea() applied to an alloca() | |
25 | result: it must be fast, to match the speed of alloca(). The speed of | |
26 | mmalloca() and freea() in the other case are not critical, because they | |
27 | are only invoked for big memory sizes. */ | |
28 | ||
29 | #if HAVE_ALLOCA | |
30 | ||
31 | /* Store the mmalloca() results in a hash table. This is needed to reliably | |
32 | distinguish a mmalloca() result and an alloca() result. | |
33 | ||
34 | Although it is possible that the same pointer is returned by alloca() and | |
35 | by mmalloca() at different times in the same application, it does not lead | |
36 | to a bug in freea(), because: | |
37 | - Before a pointer returned by alloca() can point into malloc()ed memory, | |
38 | the function must return, and once this has happened the programmer must | |
39 | not call freea() on it anyway. | |
40 | - Before a pointer returned by mmalloca() can point into the stack, it | |
41 | must be freed. The only function that can free it is freea(), and | |
42 | when freea() frees it, it also removes it from the hash table. */ | |
43 | ||
44 | #define MAGIC_NUMBER 0x1415fb4a | |
45 | #define MAGIC_SIZE sizeof (int) | |
46 | /* This is how the header info would look like without any alignment | |
47 | considerations. */ | |
48 | struct preliminary_header { void *next; char room[MAGIC_SIZE]; }; | |
49 | /* But the header's size must be a multiple of sa_alignment_max. */ | |
50 | #define HEADER_SIZE \ | |
51 | (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max) | |
52 | struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; }; | |
53 | /* Verify that HEADER_SIZE == sizeof (struct header). */ | |
54 | typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1]; | |
55 | /* We make the hash table quite big, so that during lookups the probability | |
56 | of empty hash buckets is quite high. There is no need to make the hash | |
57 | table resizable, because when the hash table gets filled so much that the | |
58 | lookup becomes slow, it means that the application has memory leaks. */ | |
59 | #define HASH_TABLE_SIZE 257 | |
60 | static void * mmalloca_results[HASH_TABLE_SIZE]; | |
61 | ||
62 | #endif | |
63 | ||
64 | void * | |
65 | mmalloca (size_t n) | |
66 | { | |
67 | #if HAVE_ALLOCA | |
68 | /* Allocate one more word, that serves as an indicator for malloc()ed | |
69 | memory, so that freea() of an alloca() result is fast. */ | |
70 | size_t nplus = n + HEADER_SIZE; | |
71 | ||
72 | if (nplus >= n) | |
73 | { | |
74 | char *p = (char *) malloc (nplus); | |
75 | ||
76 | if (p != NULL) | |
77 | { | |
78 | size_t slot; | |
79 | ||
80 | p += HEADER_SIZE; | |
81 | ||
82 | /* Put a magic number into the indicator word. */ | |
83 | ((int *) p)[-1] = MAGIC_NUMBER; | |
84 | ||
85 | /* Enter p into the hash table. */ | |
86 | slot = (unsigned long) p % HASH_TABLE_SIZE; | |
87 | ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot]; | |
88 | mmalloca_results[slot] = p; | |
89 | ||
90 | return p; | |
91 | } | |
92 | } | |
93 | /* Out of memory. */ | |
94 | return NULL; | |
95 | #else | |
96 | # if !MALLOC_0_IS_NONNULL | |
97 | if (n == 0) | |
98 | n = 1; | |
99 | # endif | |
100 | return malloc (n); | |
101 | #endif | |
102 | } | |
103 | ||
104 | #if HAVE_ALLOCA | |
105 | void | |
106 | freea (void *p) | |
107 | { | |
108 | /* mmalloca() may have returned NULL. */ | |
109 | if (p != NULL) | |
110 | { | |
111 | /* Attempt to quickly distinguish the mmalloca() result - which has | |
112 | a magic indicator word - and the alloca() result - which has an | |
113 | uninitialized indicator word. It is for this test that sa_increment | |
114 | additional bytes are allocated in the alloca() case. */ | |
115 | if (((int *) p)[-1] == MAGIC_NUMBER) | |
116 | { | |
117 | /* Looks like a mmalloca() result. To see whether it really is one, | |
118 | perform a lookup in the hash table. */ | |
119 | size_t slot = (unsigned long) p % HASH_TABLE_SIZE; | |
120 | void **chain = &mmalloca_results[slot]; | |
121 | for (; *chain != NULL;) | |
122 | { | |
123 | if (*chain == p) | |
124 | { | |
125 | /* Found it. Remove it from the hash table and free it. */ | |
126 | char *p_begin = (char *) p - HEADER_SIZE; | |
127 | *chain = ((struct header *) p_begin)->next; | |
128 | free (p_begin); | |
129 | return; | |
130 | } | |
131 | chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next; | |
132 | } | |
133 | } | |
134 | /* At this point, we know it was not a mmalloca() result. */ | |
135 | } | |
136 | } | |
137 | #endif |