[PATCH v6 05/39] ring: use C11 alignas

[Konstantin Ananyev]

> Subject: [PATCH v6 05/39] ring: use C11 alignas
> 
> The current location used for __rte_aligned(a) for alignment of types
> and variables is not compatible with MSVC. There is only a single
> location accepted by both toolchains.
> 
> For variables standard C11 offers alignas(a) supported by conformant
> compilers i.e. both MSVC and GCC.
> 
> For types the standard offers no alignment facility that compatibly
> interoperates with C and C++ but may be achieved by relocating the
> placement of __rte_aligned(a) to the aforementioned location accepted
> by all currently supported toolchains.
> 
> To allow alignment for both compilers do the following:
> 
> * Move __rte_aligned from the end of {struct,union} definitions to
>   be between {struct,union} and tag.
> 
>   The placement between {struct,union} and the tag allows the desired
>   alignment to be imparted on the type regardless of the toolchain being
>   used for all of GCC, LLVM, MSVC compilers building both C and C++.
> 
> * Replace use of __rte_aligned(a) on variables/fields with alignas(a).
> 
> Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> Acked-by: Morten Brørup <mb at smartsharesystems.com>
> ---
>  lib/ring/rte_ring_core.h    | 16 +++++++++-------
>  lib/ring/rte_ring_peek_zc.h |  4 ++--
>  2 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/lib/ring/rte_ring_core.h b/lib/ring/rte_ring_core.h
> index b770873..f958064 100644
> --- a/lib/ring/rte_ring_core.h
> +++ b/lib/ring/rte_ring_core.h
> @@ -19,6 +19,8 @@
>   * instead.
>   */
> 
> +#include <stdalign.h>
> +
>  #ifdef __cplusplus
>  extern "C" {
>  #endif
> @@ -78,7 +80,7 @@ struct rte_ring_headtail {
> 
>  union __rte_ring_rts_poscnt {
>  	/** raw 8B value to read/write *cnt* and *pos* as one atomic op */
> -	RTE_ATOMIC(uint64_t) raw __rte_aligned(8);
> +	alignas(sizeof(uint64_t)) RTE_ATOMIC(uint64_t) raw;
>  	struct {
>  		uint32_t cnt; /**< head/tail reference counter */
>  		uint32_t pos; /**< head/tail position */
> @@ -94,7 +96,7 @@ struct rte_ring_rts_headtail {
> 
>  union __rte_ring_hts_pos {
>  	/** raw 8B value to read/write *head* and *tail* as one atomic op */
> -	RTE_ATOMIC(uint64_t) raw __rte_aligned(8);
> +	alignas(sizeof(uint64_t)) RTE_ATOMIC(uint64_t) raw;
>  	struct {
>  		RTE_ATOMIC(uint32_t) head; /**< head position */
>  		RTE_ATOMIC(uint32_t) tail; /**< tail position */
> @@ -117,7 +119,7 @@ struct rte_ring_hts_headtail {
>   * a problem.
>   */
>  struct rte_ring {
> -	char name[RTE_RING_NAMESIZE] __rte_cache_aligned;
> +	alignas(RTE_CACHE_LINE_SIZE) char name[RTE_RING_NAMESIZE];
>  	/**< Name of the ring. */
>  	int flags;               /**< Flags supplied at creation. */
>  	const struct rte_memzone *memzone;
> @@ -129,20 +131,20 @@ struct rte_ring {
>  	RTE_CACHE_GUARD;
> 
>  	/** Ring producer status. */
> -	union {
> +	union __rte_cache_aligned {
>  		struct rte_ring_headtail prod;
>  		struct rte_ring_hts_headtail hts_prod;
>  		struct rte_ring_rts_headtail rts_prod;
> -	}  __rte_cache_aligned;
> +	};
> 
>  	RTE_CACHE_GUARD;
> 
>  	/** Ring consumer status. */
> -	union {
> +	union __rte_cache_aligned {
>  		struct rte_ring_headtail cons;
>  		struct rte_ring_hts_headtail hts_cons;
>  		struct rte_ring_rts_headtail rts_cons;
> -	}  __rte_cache_aligned;
> +	};
> 
>  	RTE_CACHE_GUARD;
>  };
> diff --git a/lib/ring/rte_ring_peek_zc.h b/lib/ring/rte_ring_peek_zc.h
> index 8fb279c..0b5e34b 100644
> --- a/lib/ring/rte_ring_peek_zc.h
> +++ b/lib/ring/rte_ring_peek_zc.h
> @@ -79,7 +79,7 @@
>   * This structure contains the pointers and length of the space
>   * reserved on the ring storage.
>   */
> -struct rte_ring_zc_data {
> +struct __rte_cache_aligned rte_ring_zc_data {
>  	/* Pointer to the first space in the ring */
>  	void *ptr1;
>  	/* Pointer to the second space in the ring if there is wrap-around.
> @@ -92,7 +92,7 @@ struct rte_ring_zc_data {
>  	 * will give the number of elements available at ptr2.
>  	 */
>  	unsigned int n1;
> -} __rte_cache_aligned;
> +};
> 
>  static __rte_always_inline void
>  __rte_ring_get_elem_addr(struct rte_ring *r, uint32_t head,
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev at huawei.com>
 

> 1.8.3.1