1 /* Safe automatic memory allocation. 2 Copyright (C) 2003-2007, 2009-2022 Free Software Foundation, Inc. 3 Written by Bruno Haible <bruno@clisp.org>, 2003. 4 5 This file is free software: you can redistribute it and/or modify 6 it under the terms of the GNU Lesser General Public License as 7 published by the Free Software Foundation; either version 2.1 of the 8 License, or (at your option) any later version. 9 10 This file 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 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser 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 /* Free a block of memory allocated through malloca(). */ 55 #if HAVE_ALLOCA 56 extern void freea (void *p); 57 #else 58 # define freea free 59 #endif 60 61 /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of 62 memory allocated on the stack, that must be freed using freea() before 63 the function returns. Upon failure, it returns NULL. */ 64 #if HAVE_ALLOCA 65 # define malloca(N) \ 66 ((N) < 4032 - (2 * sa_alignment_max - 1) \ 67 ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \ 68 + (2 * sa_alignment_max - 1)) \ 69 & ~(uintptr_t)(2 * sa_alignment_max - 1)) \ 70 : mmalloca (N)) 71 #else 72 # define malloca(N) \ 73 mmalloca (N) 74 #endif 75 extern void *mmalloca (size_t n) 76 _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (freea, 1) 77 _GL_ATTRIBUTE_ALLOC_SIZE ((1)); 78 79 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S). 80 It allocates an array of N objects, each with S bytes of memory, 81 on the stack. N and S should be nonnegative and free of side effects. 82 The array must be freed using freea() before the function returns. */ 83 #define nmalloca(n, s) \ 84 (xalloc_oversized (n, s) ? NULL : malloca ((n) * (size_t) (s))) 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 __clang__ || 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 sa_alignment_longlong = sa_alignof (long long), 119 sa_alignment_longdouble = sa_alignof (long double), 120 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 121 | (sa_alignment_longlong - 1) 122 | (sa_alignment_longdouble - 1) 123 ) + 1 124 }; 125 126 #endif /* _MALLOCA_H */ 127