1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
/* Safe automatic memory allocation.
Copyright (C) 2003, 2006-2007, 2009-2017 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2003.
This program is free software: you can redistribute it and/or
modify it under the terms of either:
* the GNU Lesser General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your
option) any later version.
or
* the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.
or both in parallel, as here.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, see <https://www.gnu.org/licenses/>. */
#define _GL_USE_STDLIB_ALLOC 1
#include <config.h>
/* Specification. */
#include "malloca.h"
#include <stdint.h>
#include "verify.h"
/* Silence a warning from clang's MemorySanitizer. */
#if defined __has_feature
# if __has_feature(memory_sanitizer)
# define NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
# endif
#endif
#ifndef NO_SANITIZE_MEMORY
# define NO_SANITIZE_MEMORY
#endif
/* The speed critical point in this file is freea() applied to an alloca()
result: it must be fast, to match the speed of alloca(). The speed of
mmalloca() and freea() in the other case are not critical, because they
are only invoked for big memory sizes. */
#if HAVE_ALLOCA
/* Store the mmalloca() results in a hash table. This is needed to reliably
distinguish a mmalloca() result and an alloca() result.
Although it is possible that the same pointer is returned by alloca() and
by mmalloca() at different times in the same application, it does not lead
to a bug in freea(), because:
- Before a pointer returned by alloca() can point into malloc()ed memory,
the function must return, and once this has happened the programmer must
not call freea() on it anyway.
- Before a pointer returned by mmalloca() can point into the stack, it
must be freed. The only function that can free it is freea(), and
when freea() frees it, it also removes it from the hash table. */
#define MAGIC_NUMBER 0x1415fb4a
#define MAGIC_SIZE sizeof (int)
/* This is how the header info would look like without any alignment
considerations. */
struct preliminary_header { void *next; int magic; };
/* But the header's size must be a multiple of sa_alignment_max. */
#define HEADER_SIZE \
(((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
union header {
void *next;
struct {
char room[HEADER_SIZE - MAGIC_SIZE];
int word;
} magic;
};
verify (HEADER_SIZE == sizeof (union header));
/* We make the hash table quite big, so that during lookups the probability
of empty hash buckets is quite high. There is no need to make the hash
table resizable, because when the hash table gets filled so much that the
lookup becomes slow, it means that the application has memory leaks. */
#define HASH_TABLE_SIZE 257
static void * mmalloca_results[HASH_TABLE_SIZE];
#endif
void *
mmalloca (size_t n)
{
#if HAVE_ALLOCA
/* Allocate one more word, that serves as an indicator for malloc()ed
memory, so that freea() of an alloca() result is fast. */
size_t nplus = n + HEADER_SIZE;
if (nplus >= n)
{
void *p = malloc (nplus);
if (p != NULL)
{
size_t slot;
union header *h = p;
p = h + 1;
/* Put a magic number into the indicator word. */
h->magic.word = MAGIC_NUMBER;
/* Enter p into the hash table. */
slot = (uintptr_t) p % HASH_TABLE_SIZE;
h->next = mmalloca_results[slot];
mmalloca_results[slot] = p;
return p;
}
}
/* Out of memory. */
return NULL;
#else
# if !MALLOC_0_IS_NONNULL
if (n == 0)
n = 1;
# endif
return malloc (n);
#endif
}
#if HAVE_ALLOCA
void NO_SANITIZE_MEMORY
freea (void *p)
{
/* mmalloca() may have returned NULL. */
if (p != NULL)
{
/* Attempt to quickly distinguish the mmalloca() result - which has
a magic indicator word - and the alloca() result - which has an
uninitialized indicator word. It is for this test that sa_increment
additional bytes are allocated in the alloca() case. */
if (((int *) p)[-1] == MAGIC_NUMBER)
{
/* Looks like a mmalloca() result. To see whether it really is one,
perform a lookup in the hash table. */
size_t slot = (uintptr_t) p % HASH_TABLE_SIZE;
void **chain = &mmalloca_results[slot];
for (; *chain != NULL;)
{
union header *h = p;
if (*chain == p)
{
/* Found it. Remove it from the hash table and free it. */
union header *p_begin = h - 1;
*chain = p_begin->next;
free (p_begin);
return;
}
h = *chain;
chain = &h[-1].next;
}
}
/* At this point, we know it was not a mmalloca() result. */
}
}
#endif
|