| 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 */ |