1 /* Safe automatic memory allocation. 2 Copyright (C) 2003-2004 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 2, 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, write to the Free Software Foundation, 17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 18 19 #ifndef _ALLOCSA_H 20 #define _ALLOCSA_H 21 22 #include <alloca.h> 23 #include <stddef.h> 24 #include <stdlib.h> 25 26 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 27 alloca(N); otherwise it returns NULL. It either returns N bytes of 28 memory allocated on the stack, that lasts until the function returns, 29 or NULL. 30 Use of safe_alloca should be avoided: 31 - inside arguments of function calls - undefined behaviour, 32 - in inline functions - the allocation may actually last until the 33 calling function returns. 34 */ 35 #if HAVE_ALLOCA 36 /* The OS usually guarantees only one guard page at the bottom of the stack, 37 and a page size can be as small as 4096 bytes. So we cannot safely 38 allocate anything larger than 4096 bytes. Also care for the possibility 39 of a few compiler-allocated temporary stack slots. 40 This must be a macro, not an inline function. */ 41 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 42 #else 43 # define safe_alloca(N) ((N), NULL) 44 #endif 45 46 /* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of 47 memory allocated on the stack, that must be freed using freesa() before 48 the function returns. Upon failure, it returns NULL. */ 49 #if HAVE_ALLOCA 50 # define allocsa(N) \ 51 ((N) < 4032 - sa_increment \ 52 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 53 : mallocsa (N)) 54 #else 55 # define allocsa(N) \ 56 mallocsa (N) 57 #endif 58 extern void * mallocsa (size_t n); 59 60 /* Free a block of memory allocated through allocsa(). */ 61 #if HAVE_ALLOCA 62 extern void freesa (void *p); 63 #else 64 # define freesa free 65 #endif 66 67 /* Maybe we should also define a variant 68 nallocsa (size_t n, size_t s) - behaves like allocsa (n * s) 69 If this would be useful in your application. please speak up. */ 70 71 72 /* ------------------- Auxiliary, non-public definitions ------------------- */ 73 74 /* Determine the alignment of a type at compile time. */ 75 #if defined __GNUC__ 76 # define sa_alignof __alignof__ 77 #elif defined __cplusplus 78 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 79 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 80 #elif defined __hpux 81 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 82 values. */ 83 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 84 #else 85 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 86 #endif 87 88 enum 89 { 90 /* The desired alignment of memory allocations is the maximum alignment 91 among all elementary types. */ 92 sa_alignment_long = sa_alignof (long), 93 sa_alignment_double = sa_alignof (double), 94 #ifdef HAVE_LONG_LONG 95 sa_alignment_longlong = sa_alignof (long long), 96 #endif 97 #ifdef HAVE_LONG_DOUBLE 98 sa_alignment_longdouble = sa_alignof (long double), 99 #endif 100 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 101 #ifdef HAVE_LONG_LONG 102 | (sa_alignment_longlong - 1) 103 #endif 104 #ifdef HAVE_LONG_DOUBLE 105 | (sa_alignment_longdouble - 1) 106 #endif 107 ) + 1, 108 /* The increment that guarantees room for a magic word must be >= sizeof (int) 109 and a multiple of sa_alignment_max. */ 110 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max 111 }; 112 113 #endif /* _ALLOCSA_H */ 114