[PATCH] eal: use C11 alignas instead of GCC attribute aligned

[Bruce Richardson]

On Wed, Nov 15, 2023 at 09:39:57AM -0800, Tyler Retzlaff wrote:
> Now that we have enabled C11 replace the use of __rte_cache_aligned
> and __rte_aligned(n) with alignas(RTE_CACHE_LINE_SIZE) and
> __rte_aligned(n) respectively.

alignas(n)

> 
> Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> ---
>  lib/eal/arm/include/rte_vect.h       | 4 +++-
>  lib/eal/common/malloc_elem.h         | 4 +++-
>  lib/eal/common/malloc_heap.h         | 4 +++-
>  lib/eal/common/rte_keepalive.c       | 4 +++-
>  lib/eal/common/rte_random.c          | 5 ++++-
>  lib/eal/common/rte_service.c         | 7 +++++--
>  lib/eal/include/generic/rte_atomic.h | 4 +++-
>  lib/eal/loongarch/include/rte_vect.h | 7 +++++--
>  lib/eal/ppc/include/rte_vect.h       | 5 ++++-
>  lib/eal/riscv/include/rte_vect.h     | 4 +++-
>  lib/eal/x86/include/rte_vect.h       | 4 +++-
>  lib/eal/x86/rte_power_intrinsics.c   | 8 ++++++--
>  12 files changed, 45 insertions(+), 15 deletions(-)
> 
> diff --git a/lib/eal/arm/include/rte_vect.h b/lib/eal/arm/include/rte_vect.h
> index 8cfe4bd..c7a3b2e 100644
> --- a/lib/eal/arm/include/rte_vect.h
> +++ b/lib/eal/arm/include/rte_vect.h
> @@ -5,6 +5,7 @@
>  #ifndef _RTE_VECT_ARM_H_
>  #define _RTE_VECT_ARM_H_
>  
> +#include <stdalign.h>
>  #include <stdint.h>
>  #include "generic/rte_vect.h"
>  #include "rte_debug.h"
> @@ -25,13 +26,14 @@
>  #define	XMM_MASK	(XMM_SIZE - 1)
>  
>  typedef union rte_xmm {
> +	alignas(16)
>  	xmm_t    x;
>  	uint8_t  u8[XMM_SIZE / sizeof(uint8_t)];

This may seem minor but I really don't like the indentation style used for
these alignas statements. To a casual glance they look like elements in the
struct. The previous macros were nice is that it was hard to mistake them
for anything other than additional info on the struct.

Couple of suggestions:
1. Put them on the same line as the definition of the first element. The
   downside is that we lose the (as here) implication that it's the struct
   being aligned more than just the first element.
2. Alternatively, how about putting the alignas on the same line as the
   struct/union e.g.

	struct rte_xyz {   alignas(16)
		...
	}

   In this case, or perhaps generally, perhaps we want to define
rte_aliases with underscores for these alignas to further visually separate
them.

Thoughts?

/Bruce