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1/* SPDX-License-Identifier: GPL-2.0 OR MIT */2#ifndef __LINUX_OVERFLOW_H3#define __LINUX_OVERFLOW_H4 5#include <linux/compiler.h>6 7/*8 * We need to compute the minimum and maximum values representable in a given9 * type. These macros may also be useful elsewhere. It would seem more obvious10 * to do something like:11 *12 * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)13 * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)14 *15 * Unfortunately, the middle expressions, strictly speaking, have16 * undefined behaviour, and at least some versions of gcc warn about17 * the type_max expression (but not if -fsanitize=undefined is in18 * effect; in that case, the warning is deferred to runtime...).19 *20 * The slightly excessive casting in type_min is to make sure the21 * macros also produce sensible values for the exotic type _Bool. [The22 * overflow checkers only almost work for _Bool, but that's23 * a-feature-not-a-bug, since people shouldn't be doing arithmetic on24 * _Bools. Besides, the gcc builtins don't allow _Bool* as third25 * argument.]26 *27 * Idea stolen from28 * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -29 * credit to Christian Biere.30 */31#define is_signed_type(type) (((type)(-1)) < (type)1)32#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))33#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))34#define type_min(T) ((T)((T)-type_max(T)-(T)1))35 36/*37 * For simplicity and code hygiene, the fallback code below insists on38 * a, b and *d having the same type (similar to the min() and max()39 * macros), whereas gcc's type-generic overflow checkers accept40 * different types. Hence we don't just make check_add_overflow an41 * alias for __builtin_add_overflow, but add type checks similar to42 * below.43 */44#define check_add_overflow(a, b, d) ({ \45 typeof(a) __a = (a); \46 typeof(b) __b = (b); \47 typeof(d) __d = (d); \48 (void) (&__a == &__b); \49 (void) (&__a == __d); \50 __builtin_add_overflow(__a, __b, __d); \51})52 53#define check_sub_overflow(a, b, d) ({ \54 typeof(a) __a = (a); \55 typeof(b) __b = (b); \56 typeof(d) __d = (d); \57 (void) (&__a == &__b); \58 (void) (&__a == __d); \59 __builtin_sub_overflow(__a, __b, __d); \60})61 62#define check_mul_overflow(a, b, d) ({ \63 typeof(a) __a = (a); \64 typeof(b) __b = (b); \65 typeof(d) __d = (d); \66 (void) (&__a == &__b); \67 (void) (&__a == __d); \68 __builtin_mul_overflow(__a, __b, __d); \69})70 71/**72 * array_size() - Calculate size of 2-dimensional array.73 *74 * @a: dimension one75 * @b: dimension two76 *77 * Calculates size of 2-dimensional array: @a * @b.78 *79 * Returns: number of bytes needed to represent the array or SIZE_MAX on80 * overflow.81 */82static inline __must_check size_t array_size(size_t a, size_t b)83{84 size_t bytes;85 86 if (check_mul_overflow(a, b, &bytes))87 return SIZE_MAX;88 89 return bytes;90}91 92/**93 * array3_size() - Calculate size of 3-dimensional array.94 *95 * @a: dimension one96 * @b: dimension two97 * @c: dimension three98 *99 * Calculates size of 3-dimensional array: @a * @b * @c.100 *101 * Returns: number of bytes needed to represent the array or SIZE_MAX on102 * overflow.103 */104static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)105{106 size_t bytes;107 108 if (check_mul_overflow(a, b, &bytes))109 return SIZE_MAX;110 if (check_mul_overflow(bytes, c, &bytes))111 return SIZE_MAX;112 113 return bytes;114}115 116static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)117{118 size_t bytes;119 120 if (check_mul_overflow(n, size, &bytes))121 return SIZE_MAX;122 if (check_add_overflow(bytes, c, &bytes))123 return SIZE_MAX;124 125 return bytes;126}127 128/**129 * struct_size() - Calculate size of structure with trailing array.130 * @p: Pointer to the structure.131 * @member: Name of the array member.132 * @n: Number of elements in the array.133 *134 * Calculates size of memory needed for structure @p followed by an135 * array of @n @member elements.136 *137 * Return: number of bytes needed or SIZE_MAX on overflow.138 */139#define struct_size(p, member, n) \140 __ab_c_size(n, \141 sizeof(*(p)->member) + __must_be_array((p)->member),\142 sizeof(*(p)))143 144#endif /* __LINUX_OVERFLOW_H */145