1 /* Safe automatic memory allocation.
2 Copyright (C) 2003-2007, 2009-2018 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2003.
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)
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.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, see <https://www.gnu.org/licenses/>. */
26 #include "xalloc-oversized.h"
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,
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.
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)
51 # define safe_alloca(N) ((void) (N), NULL)
54 /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of
55 memory allocated on the stack, that must be freed using freea() before
56 the function returns. Upon failure, it returns NULL. */
59 ((N) < 4032 - sa_increment \
60 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
66 extern void * mmalloca (size_t n);
68 /* Free a block of memory allocated through malloca(). */
70 extern void freea (void *p);
75 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
76 It allocates an array of N objects, each with S bytes of memory,
77 on the stack. S must be positive and N must be nonnegative.
78 The array must be freed using freea() before the function returns. */
79 #define nmalloca(n, s) (xalloc_oversized (n, s) ? NULL : malloca ((n) * (s)))
87 /* ------------------- Auxiliary, non-public definitions ------------------- */
89 /* Determine the alignment of a type at compile time. */
90 #if defined __GNUC__ || defined __IBM__ALIGNOF__
91 # define sa_alignof __alignof__
92 #elif defined __cplusplus
93 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
94 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
96 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
98 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
100 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
102 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
104 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
109 /* The desired alignment of memory allocations is the maximum alignment
110 among all elementary types. */
111 sa_alignment_long = sa_alignof (long),
112 sa_alignment_double = sa_alignof (double),
113 #if HAVE_LONG_LONG_INT
114 sa_alignment_longlong = sa_alignof (long long),
116 sa_alignment_longdouble = sa_alignof (long double),
117 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
118 #if HAVE_LONG_LONG_INT
119 | (sa_alignment_longlong - 1)
121 | (sa_alignment_longdouble - 1)
123 /* The increment that guarantees room for a magic word must be >= sizeof (int)
124 and a multiple of sa_alignment_max. */
125 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
128 #endif /* _MALLOCA_H */