RE: [PATCH v2 2/5] eal: only use numbers as align parameters for MSVC

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> -----Original Message-----
> From: Andre Muezerie <andremue@linux.microsoft.com>
> Sent: Wednesday, February 26, 2025 1:07 AM
> To: andremue@linux.microsoft.com
> Cc: dev@dpdk.org
> Subject: [PATCH v2 2/5] eal: only use numbers as align parameters for MSVC
> 
> After the instruction set updates for MSVC the error below popped up:
> 
> ..\lib\eal\x86\include\rte_vect.h(82): error C2059: syntax error: '('
> 
> The issue is that MSVC does not allow __rte_aligned(RTE_X86_ZMM_SIZE).
> It only accepts numbers that are power of 2. So, even though
> RTE_X86_ZMM_SIZE represents a number that is a power of two it cannot
> be used directly.
> https://learn.microsoft.com/en-us/cpp/cpp/align-cpp?view=msvc-170
> 
> Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> ---
>  lib/eal/x86/include/rte_vect.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/eal/x86/include/rte_vect.h b/lib/eal/x86/include/rte_vect.h
> index 70c78e9b77..0a51c539a4 100644
> --- a/lib/eal/x86/include/rte_vect.h
> +++ b/lib/eal/x86/include/rte_vect.h
> @@ -79,7 +79,16 @@ __extension__ ({                \
>  #define RTE_X86_ZMM_SIZE	(sizeof(__m512i))
>  #define RTE_X86_ZMM_MASK	(RTE_X86_ZMM_SIZE - 1)
> 
> -typedef union __rte_aligned(RTE_X86_ZMM_SIZE) __rte_x86_zmm {
> +/*
> + * MSVC does not allow __rte_aligned(RTE_X86_ZMM_SIZE). It only accepts
> + * numbers that are power of 2. So, even though RTE_X86_ZMM_SIZE represents a
> + * number that is a power of two it cannot be used directly.
> + * Ref: https://learn.microsoft.com/en-us/cpp/cpp/align-cpp?view=msvc-170
> + * The static assert below ensures that RTE_X86_ZMM_SIZE is equal to what is
> + * used in the __rte_aligned() expression.
> + */
> +static_assert(RTE_X86_ZMM_SIZE == 64, "Unexpected size of __m512i");
> +typedef union __rte_aligned(64) __rte_x86_zmm {

Just wonder, would then MSVC understand something like:
#define RTE_X86_ZMM_SIZE	64
static_assert(RTE_X86_ZMM_SIZE == sizeof((__m512i), "Unexpected size of __m512i");
typedef union __rte_aligned(RTE_X86_ZMM_SIZE) __rte_x86_zmm {
? 

>  	__m512i	 z;
>  	ymm_t    y[RTE_X86_ZMM_SIZE / sizeof(ymm_t)];
>  	xmm_t    x[RTE_X86_ZMM_SIZE / sizeof(xmm_t)];
> --
> 2.48.1.vfs.0.0