279 строки
8.2 KiB
C
279 строки
8.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 OR MIT */
|
|
#ifndef __LINUX_OVERFLOW_H
|
|
#define __LINUX_OVERFLOW_H
|
|
|
|
#include <linux/compiler.h>
|
|
|
|
/*
|
|
* In the fallback code below, we need to compute the minimum and
|
|
* maximum values representable in a given type. These macros may also
|
|
* be useful elsewhere, so we provide them outside the
|
|
* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
|
|
*
|
|
* It would seem more obvious to do something like
|
|
*
|
|
* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
|
|
* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
|
|
*
|
|
* Unfortunately, the middle expressions, strictly speaking, have
|
|
* undefined behaviour, and at least some versions of gcc warn about
|
|
* the type_max expression (but not if -fsanitize=undefined is in
|
|
* effect; in that case, the warning is deferred to runtime...).
|
|
*
|
|
* The slightly excessive casting in type_min is to make sure the
|
|
* macros also produce sensible values for the exotic type _Bool. [The
|
|
* overflow checkers only almost work for _Bool, but that's
|
|
* a-feature-not-a-bug, since people shouldn't be doing arithmetic on
|
|
* _Bools. Besides, the gcc builtins don't allow _Bool* as third
|
|
* argument.]
|
|
*
|
|
* Idea stolen from
|
|
* https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
|
|
* credit to Christian Biere.
|
|
*/
|
|
#define is_signed_type(type) (((type)(-1)) < (type)1)
|
|
#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
|
|
#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
|
|
#define type_min(T) ((T)((T)-type_max(T)-(T)1))
|
|
|
|
|
|
#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
|
|
/*
|
|
* For simplicity and code hygiene, the fallback code below insists on
|
|
* a, b and *d having the same type (similar to the min() and max()
|
|
* macros), whereas gcc's type-generic overflow checkers accept
|
|
* different types. Hence we don't just make check_add_overflow an
|
|
* alias for __builtin_add_overflow, but add type checks similar to
|
|
* below.
|
|
*/
|
|
#define check_add_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
__builtin_add_overflow(__a, __b, __d); \
|
|
})
|
|
|
|
#define check_sub_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
__builtin_sub_overflow(__a, __b, __d); \
|
|
})
|
|
|
|
#define check_mul_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
__builtin_mul_overflow(__a, __b, __d); \
|
|
})
|
|
|
|
#else
|
|
|
|
|
|
/* Checking for unsigned overflow is relatively easy without causing UB. */
|
|
#define __unsigned_add_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = __a + __b; \
|
|
*__d < __a; \
|
|
})
|
|
#define __unsigned_sub_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = __a - __b; \
|
|
__a < __b; \
|
|
})
|
|
/*
|
|
* If one of a or b is a compile-time constant, this avoids a division.
|
|
*/
|
|
#define __unsigned_mul_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = __a * __b; \
|
|
__builtin_constant_p(__b) ? \
|
|
__b > 0 && __a > type_max(typeof(__a)) / __b : \
|
|
__a > 0 && __b > type_max(typeof(__b)) / __a; \
|
|
})
|
|
|
|
/*
|
|
* For signed types, detecting overflow is much harder, especially if
|
|
* we want to avoid UB. But the interface of these macros is such that
|
|
* we must provide a result in *d, and in fact we must produce the
|
|
* result promised by gcc's builtins, which is simply the possibly
|
|
* wrapped-around value. Fortunately, we can just formally do the
|
|
* operations in the widest relevant unsigned type (u64) and then
|
|
* truncate the result - gcc is smart enough to generate the same code
|
|
* with and without the (u64) casts.
|
|
*/
|
|
|
|
/*
|
|
* Adding two signed integers can overflow only if they have the same
|
|
* sign, and overflow has happened iff the result has the opposite
|
|
* sign.
|
|
*/
|
|
#define __signed_add_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = (u64)__a + (u64)__b; \
|
|
(((~(__a ^ __b)) & (*__d ^ __a)) \
|
|
& type_min(typeof(__a))) != 0; \
|
|
})
|
|
|
|
/*
|
|
* Subtraction is similar, except that overflow can now happen only
|
|
* when the signs are opposite. In this case, overflow has happened if
|
|
* the result has the opposite sign of a.
|
|
*/
|
|
#define __signed_sub_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = (u64)__a - (u64)__b; \
|
|
((((__a ^ __b)) & (*__d ^ __a)) \
|
|
& type_min(typeof(__a))) != 0; \
|
|
})
|
|
|
|
/*
|
|
* Signed multiplication is rather hard. gcc always follows C99, so
|
|
* division is truncated towards 0. This means that we can write the
|
|
* overflow check like this:
|
|
*
|
|
* (a > 0 && (b > MAX/a || b < MIN/a)) ||
|
|
* (a < -1 && (b > MIN/a || b < MAX/a) ||
|
|
* (a == -1 && b == MIN)
|
|
*
|
|
* The redundant casts of -1 are to silence an annoying -Wtype-limits
|
|
* (included in -Wextra) warning: When the type is u8 or u16, the
|
|
* __b_c_e in check_mul_overflow obviously selects
|
|
* __unsigned_mul_overflow, but unfortunately gcc still parses this
|
|
* code and warns about the limited range of __b.
|
|
*/
|
|
|
|
#define __signed_mul_overflow(a, b, d) ({ \
|
|
typeof(a) __a = (a); \
|
|
typeof(b) __b = (b); \
|
|
typeof(d) __d = (d); \
|
|
typeof(a) __tmax = type_max(typeof(a)); \
|
|
typeof(a) __tmin = type_min(typeof(a)); \
|
|
(void) (&__a == &__b); \
|
|
(void) (&__a == __d); \
|
|
*__d = (u64)__a * (u64)__b; \
|
|
(__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
|
|
(__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
|
|
(__b == (typeof(__b))-1 && __a == __tmin); \
|
|
})
|
|
|
|
|
|
#define check_add_overflow(a, b, d) \
|
|
__builtin_choose_expr(is_signed_type(typeof(a)), \
|
|
__signed_add_overflow(a, b, d), \
|
|
__unsigned_add_overflow(a, b, d))
|
|
|
|
#define check_sub_overflow(a, b, d) \
|
|
__builtin_choose_expr(is_signed_type(typeof(a)), \
|
|
__signed_sub_overflow(a, b, d), \
|
|
__unsigned_sub_overflow(a, b, d))
|
|
|
|
#define check_mul_overflow(a, b, d) \
|
|
__builtin_choose_expr(is_signed_type(typeof(a)), \
|
|
__signed_mul_overflow(a, b, d), \
|
|
__unsigned_mul_overflow(a, b, d))
|
|
|
|
|
|
#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
|
|
|
|
/**
|
|
* array_size() - Calculate size of 2-dimensional array.
|
|
*
|
|
* @a: dimension one
|
|
* @b: dimension two
|
|
*
|
|
* Calculates size of 2-dimensional array: @a * @b.
|
|
*
|
|
* Returns: number of bytes needed to represent the array or SIZE_MAX on
|
|
* overflow.
|
|
*/
|
|
static inline __must_check size_t array_size(size_t a, size_t b)
|
|
{
|
|
size_t bytes;
|
|
|
|
if (check_mul_overflow(a, b, &bytes))
|
|
return SIZE_MAX;
|
|
|
|
return bytes;
|
|
}
|
|
|
|
/**
|
|
* array3_size() - Calculate size of 3-dimensional array.
|
|
*
|
|
* @a: dimension one
|
|
* @b: dimension two
|
|
* @c: dimension three
|
|
*
|
|
* Calculates size of 3-dimensional array: @a * @b * @c.
|
|
*
|
|
* Returns: number of bytes needed to represent the array or SIZE_MAX on
|
|
* overflow.
|
|
*/
|
|
static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
|
|
{
|
|
size_t bytes;
|
|
|
|
if (check_mul_overflow(a, b, &bytes))
|
|
return SIZE_MAX;
|
|
if (check_mul_overflow(bytes, c, &bytes))
|
|
return SIZE_MAX;
|
|
|
|
return bytes;
|
|
}
|
|
|
|
static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)
|
|
{
|
|
size_t bytes;
|
|
|
|
if (check_mul_overflow(n, size, &bytes))
|
|
return SIZE_MAX;
|
|
if (check_add_overflow(bytes, c, &bytes))
|
|
return SIZE_MAX;
|
|
|
|
return bytes;
|
|
}
|
|
|
|
/**
|
|
* struct_size() - Calculate size of structure with trailing array.
|
|
* @p: Pointer to the structure.
|
|
* @member: Name of the array member.
|
|
* @n: Number of elements in the array.
|
|
*
|
|
* Calculates size of memory needed for structure @p followed by an
|
|
* array of @n @member elements.
|
|
*
|
|
* Return: number of bytes needed or SIZE_MAX on overflow.
|
|
*/
|
|
#define struct_size(p, member, n) \
|
|
__ab_c_size(n, \
|
|
sizeof(*(p)->member) + __must_be_array((p)->member),\
|
|
sizeof(*(p)))
|
|
|
|
#endif /* __LINUX_OVERFLOW_H */
|