[Intel-gfx] [PATCH v5 1/7] drm: Move and add a few utility macros into drm util header

[Andrzej Hajda]

On 25.07.2022 11:25, Gwan-gyeong Mun wrote:
> It moves overflows_type utility macro into drm util header from i915_utils
> header. The overflows_type can be used to catch the truncation between data
> types. And it adds safe_conversion() macro which performs a type conversion
> (cast) of an source value into a new variable, checking that the
> destination is large enough to hold the source value.
> And it adds exact_type and exactly_pgoff_t macro to catch type mis-match
> while compiling.
> 
> v3: Add is_type_unsigned() macro (Mauro)
>      Modify overflows_type() macro to consider signed data types (Mauro)
>      Fix the problem that safe_conversion() macro always returns true
> v4: Fix kernel-doc markups
> 
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Nirmoy Das <nirmoy.das at intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Reviewed-by: Mauro Carvalho Chehab <mchehab at kernel.org>
> ---
>   drivers/gpu/drm/i915/i915_utils.h |  5 +-
>   include/drm/drm_util.h            | 77 +++++++++++++++++++++++++++++++
>   2 files changed, 78 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index c10d68cdc3ca..345e5b2dc1cd 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -32,6 +32,7 @@
>   #include <linux/types.h>
>   #include <linux/workqueue.h>
>   #include <linux/sched/clock.h>
> +#include <drm/drm_util.h>
>   
>   #ifdef CONFIG_X86
>   #include <asm/hypervisor.h>
> @@ -111,10 +112,6 @@ bool i915_error_injected(void);
>   #define range_overflows_end_t(type, start, size, max) \
>   	range_overflows_end((type)(start), (type)(size), (type)(max))
>   
> -/* Note we don't consider signbits :| */
> -#define overflows_type(x, T) \
> -	(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T))
> -
>   #define ptr_mask_bits(ptr, n) ({					\
>   	unsigned long __v = (unsigned long)(ptr);			\
>   	(typeof(ptr))(__v & -BIT(n));					\
> diff --git a/include/drm/drm_util.h b/include/drm/drm_util.h
> index 79952d8c4bba..1de9ee5704fa 100644
> --- a/include/drm/drm_util.h
> +++ b/include/drm/drm_util.h
> @@ -62,6 +62,83 @@
>    */
>   #define for_each_if(condition) if (!(condition)) {} else
>   
> +/**
> + * is_type_unsigned - helper for checking data type which is an unsigned data
> + * type or not
> + * @x: The data type to check
> + *
> + * Returns:
> + * True if the data type is an unsigned data type, false otherwise.
> + */
> +#define is_type_unsigned(x) ((typeof(x))-1 >= (typeof(x))0)
> +
> +/**
> + * overflows_type - helper for checking the truncation between data types
> + * @x: Source for overflow type comparison
> + * @T: Destination for overflow type comparison
> + *
> + * It compares the values and size of each data type between the first and
> + * second argument to check whether truncation can occur when assigning the
> + * first argument to the variable of the second argument.
> + * Source and Destination can be used with or without sign bit.
> + * Composite data structures such as union and structure are not considered.
> + * Enum data types are not considered.
> + * Floating point data types are not considered.
> + *
> + * Returns:
> + * True if truncation can occur, false otherwise.
> + */
> +
> +#define overflows_type(x, T) \
> +	(is_type_unsigned(x) ? \
> +		is_type_unsigned(T) ? \
> +			(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
> +			: (sizeof(x) >= sizeof(T) && (x) >> (BITS_PER_TYPE(T) - 1)) ? 1 : 0 \
> +	: is_type_unsigned(T) ? \
> +		((x) < 0) ? 1 : (sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
> +		: (sizeof(x) > sizeof(T)) ? \
> +			((x) < 0) ? (((x) * -1) >> BITS_PER_TYPE(T)) ? 1 : 0 \
> +				: ((x) >> BITS_PER_TYPE(T)) ? 1 : 0 \
> +			: 0)


It became quite big and hard to read. I wonder if we could not just 
check the effects of the conversion, sth like:
#define overflows_type(x, T) ((T)(x) != (x))

Regards
Andrzej


> +
> +/**
> + * exact_type - break compile if source type and destination value's type are
> + * not the same
> + * @T: Source type
> + * @n: Destination value
> + *
> + * It is a helper macro for a poor man's -Wconversion: only allow variables of
> + * an exact type. It determines whether the source type and destination value's
> + * type are the same while compiling, and it breaks compile if two types are
> + * not the same
> + */
> +#define exact_type(T, n) \
> +	BUILD_BUG_ON(!__builtin_constant_p(n) && !__builtin_types_compatible_p(T, typeof(n)))
> +
> +/**
> + * exactly_pgoff_t - helper to check if the type of a value is pgoff_t
> + * @n: value to compare pgoff_t type
> + *
> + * It breaks compile if the argument value's type is not pgoff_t type.
> + */
> +#define exactly_pgoff_t(n) exact_type(pgoff_t, n)
> +
> +/**
> + * safe_conversion - perform a type conversion (cast) of an source value into
> + * a new variable, checking that the destination is large enough to hold the
> + * source value.
> + * @ptr: Destination pointer address
> + * @value: Source value
> + *
> + * Returns:
> + * If the value would overflow the destination, it returns false.
> + */
> +#define safe_conversion(ptr, value) ({ \
> +	typeof(value) __v = (value); \
> +	typeof(ptr) __ptr = (ptr); \
> +	overflows_type(__v, *__ptr) ? 0 : ((*__ptr = (typeof(*__ptr))__v), 1); \
> +})
> +
>   /**
>    * drm_can_sleep - returns true if currently okay to sleep
>    *