1/* Safe automatic memory allocation. 2 Copyright (C) 2003-2007, 2009-2011 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, write to the Free Software Foundation, 17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 18 19#ifndef _MALLOCA_H 20#define _MALLOCA_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) ((void) (N), NULL) 50#endif 51 52/* malloca(N) is a safe variant of alloca(N). It allocates N bytes of 53 memory allocated on the stack, that must be freed using freea() before 54 the function returns. Upon failure, it returns NULL. */ 55#if HAVE_ALLOCA 56# define malloca(N) \ 57 ((N) < 4032 - sa_increment \ 58 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 59 : mmalloca (N)) 60#else 61# define malloca(N) \ 62 mmalloca (N) 63#endif 64extern void * mmalloca (size_t n); 65 66/* Free a block of memory allocated through malloca(). */ 67#if HAVE_ALLOCA 68extern void freea (void *p); 69#else 70# define freea free 71#endif 72 73/* nmalloca(N,S) is an overflow-safe variant of malloca (N * S). 74 It allocates an array of N objects, each with S bytes of memory, 75 on the stack. S must be positive and N must be nonnegative. 76 The array must be freed using freea() before the function returns. */ 77#if 1 78/* Cf. the definition of xalloc_oversized. */ 79# define nmalloca(n, s) \ 80 ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \ 81 ? NULL \ 82 : malloca ((n) * (s))) 83#else 84extern void * nmalloca (size_t n, size_t s); 85#endif 86 87 88#ifdef __cplusplus 89} 90#endif 91 92 93/* ------------------- Auxiliary, non-public definitions ------------------- */ 94 95/* Determine the alignment of a type at compile time. */ 96#if defined __GNUC__ 97# define sa_alignof __alignof__ 98#elif defined __cplusplus 99 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 100# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 101#elif defined __hpux 102 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 103 values. */ 104# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 105#elif defined _AIX 106 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof 107 values. */ 108# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 109#else 110# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 111#endif 112 113enum 114{ 115/* The desired alignment of memory allocations is the maximum alignment 116 among all elementary types. */ 117 sa_alignment_long = sa_alignof (long), 118 sa_alignment_double = sa_alignof (double), 119#if HAVE_LONG_LONG_INT 120 sa_alignment_longlong = sa_alignof (long long), 121#endif 122 sa_alignment_longdouble = sa_alignof (long double), 123 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 124#if HAVE_LONG_LONG_INT 125 | (sa_alignment_longlong - 1) 126#endif 127 | (sa_alignment_longdouble - 1) 128 ) + 1, 129/* The increment that guarantees room for a magic word must be >= sizeof (int) 130 and a multiple of sa_alignment_max. */ 131 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max 132}; 133 134#endif /* _MALLOCA_H */ 135