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