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

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 27 Jul 2022, Andi Shyti <andi.shyti@linux.intel.com> wrote:
> Hi,
>
> On Mon, Jul 25, 2022 at 12:25:22PM +0300, 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@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Nirmoy Das <nirmoy.das@intel.com>
>> Cc: Jani Nikula <jani.nikula@intel.com>
>> Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>
>> ---
>>  drivers/gpu/drm/i915/i915_utils.h |  5 +-
>>  include/drm/drm_util.h            | 77 +++++++++++++++++++++++++++++++
>>  2 files changed, 78 insertions(+), 4 deletions(-)
>
> Jani and Mauro suggested to have this macro in
> include/drm/drm_util.h.

I can't recall suggesting such a thing. The macros in question have
nothing specifically to do with i915 *or* drm. They are generic, and
should be in generic kernel headers.

We must stop piling up generic and generally useful stuff in our own
headers.

I thought I've been clear about this all along.


BR,
Jani.




>
> Can I please have an ack from one of the drm maintainers so that
> I can go ahead an apply this series?
>
> Thanks,
> Andi
>
>> 
>> 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)
>> +
>> +/**
>> + * 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
>>   *
>> -- 
>> 2.34.1

-- 
Jani Nikula, Intel Open Source Graphics Center