1/* Safe automatic memory allocation. 2 Copyright (C) 2003-2005 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 27#ifdef __cplusplus 28extern "C" { 29#endif 30 31 32/* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 33 alloca(N); otherwise it returns NULL. It either returns N bytes of 34 memory allocated on the stack, that lasts until the function returns, 35 or NULL. 36 Use of safe_alloca should be avoided: 37 - inside arguments of function calls - undefined behaviour, 38 - in inline functions - the allocation may actually last until the 39 calling function returns. 40*/ 41#if HAVE_ALLOCA 42/* The OS usually guarantees only one guard page at the bottom of the stack, 43 and a page size can be as small as 4096 bytes. So we cannot safely 44 allocate anything larger than 4096 bytes. Also care for the possibility 45 of a few compiler-allocated temporary stack slots. 46 This must be a macro, not an inline function. */ 47# define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 48#else 49# define safe_alloca(N) ((N), NULL) 50#endif 51 52/* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of 53 memory allocated on the stack, that must be freed using freesa() before 54 the function returns. Upon failure, it returns NULL. */ 55#if HAVE_ALLOCA 56# define allocsa(N) \ 57 ((N) < 4032 - sa_increment \ 58 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 59 : mallocsa (N)) 60#else 61# define allocsa(N) \ 62 mallocsa (N) 63#endif 64extern void * mallocsa (size_t n); 65 66/* Free a block of memory allocated through allocsa(). */ 67#if HAVE_ALLOCA 68extern void freesa (void *p); 69#else 70# define freesa free 71#endif 72 73/* Maybe we should also define a variant 74 nallocsa (size_t n, size_t s) - behaves like allocsa (n * s) 75 If this would be useful in your application. please speak up. */ 76 77 78#ifdef __cplusplus 79} 80#endif 81 82 83/* ------------------- Auxiliary, non-public definitions ------------------- */ 84 85/* Determine the alignment of a type at compile time. */ 86#if defined __GNUC__ 87# define sa_alignof __alignof__ 88#elif defined __cplusplus 89 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 90# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 91#elif defined __hpux 92 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 93 values. */ 94# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 95#elif defined _AIX 96 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof 97 values. */ 98# define sa_alignof(type) 4 99#else 100# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 101#endif 102 103enum 104{ 105/* The desired alignment of memory allocations is the maximum alignment 106 among all elementary types. */ 107 sa_alignment_long = sa_alignof (long), 108 sa_alignment_double = sa_alignof (double), 109#ifdef HAVE_LONG_LONG 110 sa_alignment_longlong = sa_alignof (long long), 111#endif 112#ifdef HAVE_LONG_DOUBLE 113 sa_alignment_longdouble = sa_alignof (long double), 114#endif 115 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 116#ifdef HAVE_LONG_LONG 117 | (sa_alignment_longlong - 1) 118#endif 119#ifdef HAVE_LONG_DOUBLE 120 | (sa_alignment_longdouble - 1) 121#endif 122 ) + 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 126}; 127 128#endif /* _ALLOCSA_H */ 129