[PATCH v6 08/39] mbuf: use C11 alignas

[Konstantin Ananyev]

> Subject: [PATCH v6 08/39] mbuf: 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/mbuf/rte_mbuf_core.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
> index 5688683..917a811 100644
> --- a/lib/mbuf/rte_mbuf_core.h
> +++ b/lib/mbuf/rte_mbuf_core.h
> @@ -463,7 +463,7 @@ enum {
>  /**
>   * The generic rte_mbuf, containing a packet mbuf.
>   */
> -struct rte_mbuf {
> +struct __rte_cache_aligned rte_mbuf {
>  	RTE_MARKER cacheline0;
> 
>  	void *buf_addr;           /**< Virtual address of segment buffer. */
> @@ -476,7 +476,7 @@ struct rte_mbuf {
>  	 * same mbuf cacheline0 layout for 32-bit and 64-bit. This makes
>  	 * working on vector drivers easier.
>  	 */
> -	rte_iova_t buf_iova __rte_aligned(sizeof(rte_iova_t));
> +	alignas(sizeof(rte_iova_t)) rte_iova_t buf_iova;
>  #else
>  	/**
>  	 * Next segment of scattered packet.
> @@ -662,7 +662,7 @@ struct rte_mbuf {
>  	uint16_t timesync;
> 
>  	uint32_t dynfield1[9]; /**< Reserved for dynamic fields. */
> -} __rte_cache_aligned;
> +};
> 
>  /**
>   * Function typedef of callback to free externally attached buffer.
> --

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

> 1.8.3.1