1 /* Safe automatic memory allocation.
2    Copyright (C) 2003-2007, 2009-2020 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 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 <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 /* 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.  */
57 #if HAVE_ALLOCA
58 # define malloca(N) \
59   ((N) < 4032 - (2 * sa_alignment_max - 1)                                   \
60    ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \
61                 + (2 * sa_alignment_max - 1))                                \
62                & ~(uintptr_t)(2 * sa_alignment_max - 1))                     \
63    : mmalloca (N))
64 #else
65 # define malloca(N) \
66   mmalloca (N)
67 #endif
68 extern void * mmalloca (size_t n);
69 
70 /* Free a block of memory allocated through malloca().  */
71 #if HAVE_ALLOCA
72 extern void freea (void *p);
73 #else
74 # define freea free
75 #endif
76 
77 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
78    It allocates an array of N objects, each with S bytes of memory,
79    on the stack.  S must be positive and N must be nonnegative.
80    The array must be freed using freea() before the function returns.  */
81 #define nmalloca(n, s) (xalloc_oversized (n, s) ? NULL : malloca ((n) * (s)))
82 
83 
84 #ifdef __cplusplus
85 }
86 #endif
87 
88 
89 /* ------------------- Auxiliary, non-public definitions ------------------- */
90 
91 /* Determine the alignment of a type at compile time.  */
92 #if defined __GNUC__ || defined __IBM__ALIGNOF__
93 # define sa_alignof __alignof__
94 #elif defined __cplusplus
95   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
96 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
97 #elif defined __hpux
98   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
99      values.  */
100 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
101 #elif defined _AIX
102   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
103      values.  */
104 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
105 #else
106 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
107 #endif
108 
109 enum
110 {
111 /* The desired alignment of memory allocations is the maximum alignment
112    among all elementary types.  */
113   sa_alignment_long = sa_alignof (long),
114   sa_alignment_double = sa_alignof (double),
115   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                       | (sa_alignment_longlong - 1)
119                       | (sa_alignment_longdouble - 1)
120                      ) + 1
121 };
122 
123 #endif /* _MALLOCA_H */
124