1 /* Safe automatic memory allocation.
2 Copyright (C) 2003-2007, 2009-2022 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
9
10 This file 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, see <https://www.gnu.org/licenses/>. */
17
18 #ifndef _MALLOCA_H
19 #define _MALLOCA_H
20
21 #include <alloca.h>
22 #include <stddef.h>
23 #include <stdlib.h>
24 #include <stdint.h>
25
26 #include "xalloc-oversized.h"
27
28
29 #ifdef __cplusplus
30 extern "C" {
31 #endif
32
33
34 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
35 alloca(N); otherwise it returns NULL. It either returns N bytes of
36 memory allocated on the stack, that lasts until the function returns,
37 or NULL.
38 Use of safe_alloca should be avoided:
39 - inside arguments of function calls - undefined behaviour,
40 - in inline functions - the allocation may actually last until the
41 calling function returns.
42 */
43 #if HAVE_ALLOCA
44 /* The OS usually guarantees only one guard page at the bottom of the stack,
45 and a page size can be as small as 4096 bytes. So we cannot safely
46 allocate anything larger than 4096 bytes. Also care for the possibility
47 of a few compiler-allocated temporary stack slots.
48 This must be a macro, not a function. */
49 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
50 #else
51 # define safe_alloca(N) ((void) (N), NULL)
52 #endif
53
54 /* Free a block of memory allocated through malloca(). */
55 #if HAVE_ALLOCA
56 extern void freea (void *p);
57 #else
58 # define freea free
59 #endif
60
61 /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of
62 memory allocated on the stack, that must be freed using freea() before
63 the function returns. Upon failure, it returns NULL. */
64 #if HAVE_ALLOCA
65 # define malloca(N) \
66 ((N) < 4032 - (2 * sa_alignment_max - 1) \
67 ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \
68 + (2 * sa_alignment_max - 1)) \
69 & ~(uintptr_t)(2 * sa_alignment_max - 1)) \
70 : mmalloca (N))
71 #else
72 # define malloca(N) \
73 mmalloca (N)
74 #endif
75 extern void *mmalloca (size_t n)
76 _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (freea, 1)
77 _GL_ATTRIBUTE_ALLOC_SIZE ((1));
78
79 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
80 It allocates an array of N objects, each with S bytes of memory,
81 on the stack. N and S should be nonnegative and free of side effects.
82 The array must be freed using freea() before the function returns. */
83 #define nmalloca(n, s) \
84 (xalloc_oversized (n, s) ? NULL : malloca ((n) * (size_t) (s)))
85
86
87 #ifdef __cplusplus
88 }
89 #endif
90
91
92 /* ------------------- Auxiliary, non-public definitions ------------------- */
93
94 /* Determine the alignment of a type at compile time. */
95 #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
96 # define sa_alignof __alignof__
97 #elif defined __cplusplus
98 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
99 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
100 #elif defined __hpux
101 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
102 values. */
103 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
104 #elif defined _AIX
105 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
106 values. */
107 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
108 #else
109 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
110 #endif
111
112 enum
113 {
114 /* The desired alignment of memory allocations is the maximum alignment
115 among all elementary types. */
116 sa_alignment_long = sa_alignof (long),
117 sa_alignment_double = sa_alignof (double),
118 sa_alignment_longlong = sa_alignof (long long),
119 sa_alignment_longdouble = sa_alignof (long double),
120 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
121 | (sa_alignment_longlong - 1)
122 | (sa_alignment_longdouble - 1)
123 ) + 1
124 };
125
126 #endif /* _MALLOCA_H */