Re: [PATCH master 1/3] include: linux/overflow.h: sync with upstream

[Sascha Hauer <sha@pengutronix.de>]

On Fri, Oct 20, 2023 at 09:23:14AM +0200, Ahmad Fatoum wrote:
> Newer versions of the header add a size_add macro for doing saturating
> addition, which will be used in a follow-up fix, so sync the header with
> Linux to make it available.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  include/linux/overflow.h | 436 +++++++++++++++++++--------------------
>  1 file changed, 214 insertions(+), 222 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 50c93ca0c3d6..f9b60313eaea 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -4,14 +4,12 @@
>  
>  #include <linux/compiler.h>
>  #include <linux/limits.h>
> +#include <linux/const.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
> + * We need to compute the minimum and maximum values representable in a given
> + * type. These macros may also be useful elsewhere. 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)
> @@ -32,7 +30,6 @@
>   * 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))
> @@ -44,191 +41,82 @@
>  #define is_non_negative(a) ((a) > 0 || (a) == 0)
>  #define is_negative(a) (!(is_non_negative(a)))
>  
> -#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.
> + * Allows for effectively applying __must_check to a macro so we can have
> + * both the type-agnostic benefits of the macros while also being able to
> + * enforce that the return value is, in fact, checked.
>   */
> -#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);	\
> -})
> +static inline bool __must_check __must_check_overflow(bool overflow)
> +{
> +	return unlikely(overflow);
> +}
>  
> -#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:
> +/**
> + * check_add_overflow() - Calculate addition with overflow checking
> + * @a: first addend
> + * @b: second addend
> + * @d: pointer to store sum
>   *
> - * (a > 0 && (b > MAX/a || b < MIN/a)) ||
> - * (a < -1 && (b > MIN/a || b < MAX/a) ||
> - * (a == -1 && b == MIN)
> + * Returns 0 on success.
>   *
> - * 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.
> + * *@d holds the results of the attempted addition, but is not considered
> + * "safe for use" on a non-zero return value, which indicates that the
> + * sum has overflowed or been truncated.
>   */
> +#define check_add_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_add_overflow(a, b, d))
>  
> -#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 */
> -
> -/** check_shl_overflow() - Calculate a left-shifted value and check overflow
> +/**
> + * check_sub_overflow() - Calculate subtraction with overflow checking
> + * @a: minuend; value to subtract from
> + * @b: subtrahend; value to subtract from @a
> + * @d: pointer to store difference
>   *
> + * Returns 0 on success.
> + *
> + * *@d holds the results of the attempted subtraction, but is not considered
> + * "safe for use" on a non-zero return value, which indicates that the
> + * difference has underflowed or been truncated.
> + */
> +#define check_sub_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_sub_overflow(a, b, d))
> +
> +/**
> + * check_mul_overflow() - Calculate multiplication with overflow checking
> + * @a: first factor
> + * @b: second factor
> + * @d: pointer to store product
> + *
> + * Returns 0 on success.
> + *
> + * *@d holds the results of the attempted multiplication, but is not
> + * considered "safe for use" on a non-zero return value, which indicates
> + * that the product has overflowed or been truncated.
> + */
> +#define check_mul_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_mul_overflow(a, b, d))
> +
> +/**
> + * check_shl_overflow() - Calculate a left-shifted value and check overflow
>   * @a: Value to be shifted
>   * @s: How many bits left to shift
>   * @d: Pointer to where to store the result
>   *
>   * Computes *@d = (@a << @s)
>   *
> - * Returns true if '*d' cannot hold the result or when 'a << s' doesn't
> + * Returns true if '*@d' cannot hold the result or when '@a << @s' doesn't
>   * make sense. Example conditions:
> - * - 'a << s' causes bits to be lost when stored in *d.
> - * - 's' is garbage (e.g. negative) or so large that the result of
> - *   'a << s' is guaranteed to be 0.
> - * - 'a' is negative.
> - * - 'a << s' sets the sign bit, if any, in '*d'.
>   *
> - * '*d' will hold the results of the attempted shift, but is not
> - * considered "safe for use" if false is returned.
> + * - '@a << @s' causes bits to be lost when stored in *@d.
> + * - '@s' is garbage (e.g. negative) or so large that the result of
> + *   '@a << @s' is guaranteed to be 0.
> + * - '@a' is negative.
> + * - '@a << @s' sets the sign bit, if any, in '*@d'.
> + *
> + * '*@d' will hold the results of the attempted shift, but is not
> + * considered "safe for use" if true is returned.
>   */
> -#define check_shl_overflow(a, s, d) ({					\
> +#define check_shl_overflow(a, s, d) __must_check_overflow(({		\
>  	typeof(a) _a = a;						\
>  	typeof(s) _s = s;						\
>  	typeof(d) _d = d;						\
> @@ -238,11 +126,117 @@
>  	*_d = (_a_full << _to_shift);					\
>  	(_to_shift != _s || is_negative(*_d) || is_negative(_a) ||	\
>  	(*_d >> _to_shift) != _a);					\
> +}))
> +
> +#define __overflows_type_constexpr(x, T) (			\
> +	is_unsigned_type(typeof(x)) ?				\
> +		(x) > type_max(typeof(T)) :			\
> +	is_unsigned_type(typeof(T)) ?				\
> +		(x) < 0 || (x) > type_max(typeof(T)) :		\
> +	(x) < type_min(typeof(T)) || (x) > type_max(typeof(T)))
> +
> +#define __overflows_type(x, T)		({	\
> +	typeof(T) v = 0;			\
> +	check_add_overflow((x), v, &v);		\
>  })
>  
>  /**
> - * array_size() - Calculate size of 2-dimensional array.
> + * overflows_type - helper for checking the overflows between value, variables,
> + *		    or data type
>   *
> + * @n: source constant value or variable to be checked
> + * @T: destination variable or data type proposed to store @x
> + *
> + * Compares the @x expression for whether or not it can safely fit in
> + * the storage of the type in @T. @x and @T can have different types.
> + * If @x is a constant expression, this will also resolve to a constant
> + * expression.
> + *
> + * Returns: true if overflow can occur, false otherwise.
> + */
> +#define overflows_type(n, T)					\
> +	__builtin_choose_expr(__is_constexpr(n),		\
> +			      __overflows_type_constexpr(n, T),	\
> +			      __overflows_type(n, T))
> +
> +/**
> + * castable_to_type - like __same_type(), but also allows for casted literals
> + *
> + * @n: variable or constant value
> + * @T: variable or data type
> + *
> + * Unlike the __same_type() macro, this allows a constant value as the
> + * first argument. If this value would not overflow into an assignment
> + * of the second argument's type, it returns true. Otherwise, this falls
> + * back to __same_type().
> + */
> +#define castable_to_type(n, T)						\
> +	__builtin_choose_expr(__is_constexpr(n),			\
> +			      !__overflows_type_constexpr(n, T),	\
> +			      __same_type(n, T))
> +
> +/**
> + * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
> + * @factor1: first factor
> + * @factor2: second factor
> + *
> + * Returns: calculate @factor1 * @factor2, both promoted to size_t,
> + * with any overflow causing the return value to be SIZE_MAX. The
> + * lvalue must be size_t to avoid implicit type conversion.
> + */
> +static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
> +{
> +	size_t bytes;
> +
> +	if (check_mul_overflow(factor1, factor2, &bytes))
> +		return SIZE_MAX;
> +
> +	return bytes;
> +}
> +
> +/**
> + * size_add() - Calculate size_t addition with saturation at SIZE_MAX
> + * @addend1: first addend
> + * @addend2: second addend
> + *
> + * Returns: calculate @addend1 + @addend2, both promoted to size_t,
> + * with any overflow causing the return value to be SIZE_MAX. The
> + * lvalue must be size_t to avoid implicit type conversion.
> + */
> +static inline size_t __must_check size_add(size_t addend1, size_t addend2)
> +{
> +	size_t bytes;
> +
> +	if (check_add_overflow(addend1, addend2, &bytes))
> +		return SIZE_MAX;
> +
> +	return bytes;
> +}
> +
> +/**
> + * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX
> + * @minuend: value to subtract from
> + * @subtrahend: value to subtract from @minuend
> + *
> + * Returns: calculate @minuend - @subtrahend, both promoted to size_t,
> + * with any overflow causing the return value to be SIZE_MAX. For
> + * composition with the size_add() and size_mul() helpers, neither
> + * argument may be SIZE_MAX (or the result with be forced to SIZE_MAX).
> + * The lvalue must be size_t to avoid implicit type conversion.
> + */
> +static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
> +{
> +	size_t bytes;
> +
> +	if (minuend == SIZE_MAX || subtrahend == SIZE_MAX ||
> +	    check_sub_overflow(minuend, subtrahend, &bytes))
> +		return SIZE_MAX;
> +
> +	return bytes;
> +}
> +
> +/**
> + * array_size() - Calculate size of 2-dimensional array.
>   * @a: dimension one
>   * @b: dimension two
>   *
> @@ -251,19 +245,10 @@
>   * 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;
> -}
> +#define array_size(a, b)	size_mul(a, b)
>  
>  /**
>   * array3_size() - Calculate size of 3-dimensional array.
> - *
>   * @a: dimension one
>   * @b: dimension two
>   * @c: dimension three
> @@ -273,48 +258,55 @@ static inline __must_check size_t array_size(size_t a, size_t b)
>   * 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;
> -}
> -
> -/*
> - * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
> - * struct_size() below.
> - */
> -static inline __must_check size_t __ab_c_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_add_overflow(bytes, c, &bytes))
> -		return SIZE_MAX;
> -
> -	return bytes;
> -}
> +#define array3_size(a, b, c)	size_mul(size_mul(a, b), c)
>  
>  /**
> - * struct_size() - Calculate size of structure with trailing array.
> + * flex_array_size() - Calculate size of a flexible array member
> + *                     within an enclosing structure.
>   * @p: Pointer to the structure.
> - * @member: Name of the array member.
> - * @n: Number of elements in the array.
> + * @member: Name of the flexible array member.
> + * @count: Number of elements in the array.
>   *
> - * Calculates size of memory needed for structure @p followed by an
> - * array of @n @member elements.
> + * Calculates size of a flexible array of @count number of @member
> + * elements, at the end of structure @p.
>   *
>   * 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)))
> +#define flex_array_size(p, member, count)				\
> +	__builtin_choose_expr(__is_constexpr(count),			\
> +		(count) * sizeof(*(p)->member) + __must_be_array((p)->member),	\
> +		size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member)))
> +
> +/**
> + * struct_size() - Calculate size of structure with trailing flexible array.
> + * @p: Pointer to the structure.
> + * @member: Name of the array member.
> + * @count: Number of elements in the array.
> + *
> + * Calculates size of memory needed for structure of @p followed by an
> + * array of @count number of @member elements.
> + *
> + * Return: number of bytes needed or SIZE_MAX on overflow.
> + */
> +#define struct_size(p, member, count)					\
> +	__builtin_choose_expr(__is_constexpr(count),			\
> +		sizeof(*(p)) + flex_array_size(p, member, count),	\
> +		size_add(sizeof(*(p)), flex_array_size(p, member, count)))
> +
> +/**
> + * struct_size_t() - Calculate size of structure with trailing flexible array
> + * @type: structure type name.
> + * @member: Name of the array member.
> + * @count: Number of elements in the array.
> + *
> + * Calculates size of memory needed for structure @type followed by an
> + * array of @count number of @member elements. Prefer using struct_size()
> + * when possible instead, to keep calculations associated with a specific
> + * instance variable of type @type.
> + *
> + * Return: number of bytes needed or SIZE_MAX on overflow.
> + */
> +#define struct_size_t(type, member, count)					\
> +	struct_size((type *)NULL, member, count)
>  
>  #endif /* __LINUX_OVERFLOW_H */
> -- 
> 2.39.2
> 
> 
> 

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