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1 /* Safe automatic memory allocation. |
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2 Copyright (C) 2003-2007 Free Software Foundation, Inc. |
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3 Written by Bruno Haible <bruno@clisp.org>, 2003. |
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4 |
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5 This program is free software; you can redistribute it and/or modify |
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6 it under the terms of the GNU General Public License as published by |
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7 the Free Software Foundation; either version 2, or (at your option) |
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8 any later version. |
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9 |
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10 This program is distributed in the hope that it will be useful, |
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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13 GNU General Public License for more details. |
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14 |
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15 You should have received a copy of the GNU General Public License |
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16 along with this program; if not, write to the Free Software Foundation, |
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17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ |
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18 |
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19 #ifndef _MALLOCA_H |
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20 #define _MALLOCA_H |
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21 |
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22 #include <alloca.h> |
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23 #include <stddef.h> |
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24 #include <stdlib.h> |
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25 |
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26 |
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27 #ifdef __cplusplus |
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28 extern "C" { |
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29 #endif |
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30 |
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31 |
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32 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call |
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33 alloca(N); otherwise it returns NULL. It either returns N bytes of |
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34 memory allocated on the stack, that lasts until the function returns, |
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35 or NULL. |
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36 Use of safe_alloca should be avoided: |
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37 - inside arguments of function calls - undefined behaviour, |
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38 - in inline functions - the allocation may actually last until the |
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39 calling function returns. |
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40 */ |
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41 #if HAVE_ALLOCA |
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42 /* The OS usually guarantees only one guard page at the bottom of the stack, |
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43 and a page size can be as small as 4096 bytes. So we cannot safely |
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44 allocate anything larger than 4096 bytes. Also care for the possibility |
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45 of a few compiler-allocated temporary stack slots. |
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46 This must be a macro, not an inline function. */ |
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47 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) |
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48 #else |
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49 # define safe_alloca(N) ((void) (N), NULL) |
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50 #endif |
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51 |
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52 /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of |
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53 memory allocated on the stack, that must be freed using freea() before |
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54 the function returns. Upon failure, it returns NULL. */ |
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55 #if HAVE_ALLOCA |
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56 # define malloca(N) \ |
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57 ((N) < 4032 - sa_increment \ |
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58 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ |
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59 : mmalloca (N)) |
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60 #else |
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61 # define malloca(N) \ |
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62 mmalloca (N) |
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63 #endif |
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64 extern void * mmalloca (size_t n); |
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65 |
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66 /* Free a block of memory allocated through malloca(). */ |
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67 #if HAVE_ALLOCA |
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68 extern void freea (void *p); |
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69 #else |
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70 # define freea free |
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71 #endif |
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72 |
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73 /* Maybe we should also define a variant |
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74 nmalloca (size_t n, size_t s) - behaves like malloca (n * s) |
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75 If this would be useful in your application. please speak up. */ |
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76 |
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77 |
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78 #ifdef __cplusplus |
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79 } |
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80 #endif |
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81 |
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82 |
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83 /* ------------------- Auxiliary, non-public definitions ------------------- */ |
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84 |
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85 /* Determine the alignment of a type at compile time. */ |
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86 #if defined __GNUC__ |
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87 # define sa_alignof __alignof__ |
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88 #elif defined __cplusplus |
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89 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; |
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90 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) |
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91 #elif defined __hpux |
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92 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof |
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93 values. */ |
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94 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) |
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95 #elif defined _AIX |
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96 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof |
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97 values. */ |
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98 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) |
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99 #else |
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100 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) |
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101 #endif |
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102 |
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103 enum |
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104 { |
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105 /* The desired alignment of memory allocations is the maximum alignment |
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106 among all elementary types. */ |
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107 sa_alignment_long = sa_alignof (long), |
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108 sa_alignment_double = sa_alignof (double), |
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109 #if HAVE_LONG_LONG_INT |
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110 sa_alignment_longlong = sa_alignof (long long), |
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111 #endif |
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112 sa_alignment_longdouble = sa_alignof (long double), |
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113 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) |
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114 #if HAVE_LONG_LONG_INT |
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115 | (sa_alignment_longlong - 1) |
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116 #endif |
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117 | (sa_alignment_longdouble - 1) |
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118 ) + 1, |
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119 /* The increment that guarantees room for a magic word must be >= sizeof (int) |
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120 and a multiple of sa_alignment_max. */ |
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121 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max |
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122 }; |
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123 |
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124 #endif /* _MALLOCA_H */ |
