Re: [Intel-gfx] [PATCH] drm/i915: remove struct_member macro

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 09/12/2022 12:14, Andrzej Hajda wrote:
> Since it is used only to get type of member it can be replaced
> with typeof_member.
> 
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_utils.h       | 4 +---
>   drivers/gpu/drm/i915/intel_runtime_pm.h | 2 +-
>   2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 6c14d13364bf78..b64192d9c7daa7 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -149,8 +149,6 @@ bool i915_error_injected(void);
>   #define page_pack_bits(ptr, bits) ptr_pack_bits(ptr, bits, PAGE_SHIFT)
>   #define page_unpack_bits(ptr, bits) ptr_unpack_bits(ptr, bits, PAGE_SHIFT)
>   
> -#define struct_member(T, member) (((T *)0)->member)
> -
>   #define fetch_and_zero(ptr) ({						\
>   	typeof(*ptr) __T = *(ptr);					\
>   	*(ptr) = (typeof(*ptr))0;					\
> @@ -170,7 +168,7 @@ static __always_inline ptrdiff_t ptrdiff(const void *a, const void *b)
>    */
>   #define container_of_user(ptr, type, member) ({				\
>   	void __user *__mptr = (void __user *)(ptr);			\
> -	BUILD_BUG_ON_MSG(!__same_type(*(ptr), struct_member(type, member)) && \
> +	BUILD_BUG_ON_MSG(!__same_type(*(ptr), typeof_member(type, member)) && \

#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))

#define typeof_member(T, m)	typeof(((T*)0)->m)

So expands to:

__builtin_types_compatible_p(typeof(*(ptr)), typeof(typeof(((type*)0)->m)));

I guess that's okay since infinite number of typeofs is still a typeof.

Regards,

Tvrtko

>   			 !__same_type(*(ptr), void),			\
>   			 "pointer type mismatch in container_of()");	\
>   	((type __user *)(__mptr - offsetof(type, member))); })
> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.h b/drivers/gpu/drm/i915/intel_runtime_pm.h
> index 98b8b28baaa15e..e592e8d6499a1f 100644
> --- a/drivers/gpu/drm/i915/intel_runtime_pm.h
> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.h
> @@ -96,7 +96,7 @@ struct intel_runtime_pm {
>   };
>   
>   #define BITS_PER_WAKEREF	\
> -	BITS_PER_TYPE(struct_member(struct intel_runtime_pm, wakeref_count))
> +	BITS_PER_TYPE(typeof_member(struct intel_runtime_pm, wakeref_count))
>   #define INTEL_RPM_WAKELOCK_SHIFT	(BITS_PER_WAKEREF / 2)
>   #define INTEL_RPM_WAKELOCK_BIAS		(1 << INTEL_RPM_WAKELOCK_SHIFT)
>   #define INTEL_RPM_RAW_WAKEREF_MASK	(INTEL_RPM_WAKELOCK_BIAS - 1)