1 /* Safe automatic memory allocation. 2 Copyright (C) 2003-2007, 2009-2015 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 <http://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 25 26 #ifdef __cplusplus 27 extern "C" { 28 #endif 29 30 31 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 32 alloca(N); otherwise it returns NULL. It either returns N bytes of 33 memory allocated on the stack, that lasts until the function returns, 34 or NULL. 35 Use of safe_alloca should be avoided: 36 - inside arguments of function calls - undefined behaviour, 37 - in inline functions - the allocation may actually last until the 38 calling function returns. 39 */ 40 #if HAVE_ALLOCA 41 /* The OS usually guarantees only one guard page at the bottom of the stack, 42 and a page size can be as small as 4096 bytes. So we cannot safely 43 allocate anything larger than 4096 bytes. Also care for the possibility 44 of a few compiler-allocated temporary stack slots. 45 This must be a macro, not a function. */ 46 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 47 #else 48 # define safe_alloca(N) ((void) (N), NULL) 49 #endif 50 51 /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of 52 memory allocated on the stack, that must be freed using freea() before 53 the function returns. Upon failure, it returns NULL. */ 54 #if HAVE_ALLOCA 55 # define malloca(N) \ 56 ((N) < 4032 - sa_increment \ 57 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 58 : mmalloca (N)) 59 #else 60 # define malloca(N) \ 61 mmalloca (N) 62 #endif 63 extern void * mmalloca (size_t n); 64 65 /* Free a block of memory allocated through malloca(). */ 66 #if HAVE_ALLOCA 67 extern void freea (void *p); 68 #else 69 # define freea free 70 #endif 71 72 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S). 73 It allocates an array of N objects, each with S bytes of memory, 74 on the stack. S must be positive and N must be nonnegative. 75 The array must be freed using freea() before the function returns. */ 76 #if 1 77 /* Cf. the definition of xalloc_oversized. */ 78 # define nmalloca(n, s) \ 79 ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \ 80 ? NULL \ 81 : malloca ((n) * (s))) 82 #else 83 extern void * nmalloca (size_t n, size_t s); 84 #endif 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 __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 #if HAVE_LONG_LONG_INT 119 sa_alignment_longlong = sa_alignof (long long), 120 #endif 121 sa_alignment_longdouble = sa_alignof (long double), 122 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 123 #if HAVE_LONG_LONG_INT 124 | (sa_alignment_longlong - 1) 125 #endif 126 | (sa_alignment_longdouble - 1) 127 ) + 1, 128 /* The increment that guarantees room for a magic word must be >= sizeof (int) 129 and a multiple of sa_alignment_max. */ 130 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max 131 }; 132 133 #endif /* _MALLOCA_H */ 134