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Subject: RE: [PATCH v4 19/35] eal: add macro for marking assumed alignment
Date: Mon, 9 Feb 2026 23:35:26 +0100
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Thread-Topic: [PATCH v4 19/35] eal: add macro for marking assumed alignment
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Bruce Richardson" <bruce.richardson@intel.com>,
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> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Monday, 9 February 2026 17.45
>=20
> Provide a common DPDK macro for the gcc/clang builtin
> __rte_assume_aligned to mark pointers as pointing to something with
> known minimum alignment.
>=20
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  lib/eal/include/rte_common.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>=20
> diff --git a/lib/eal/include/rte_common.h
> b/lib/eal/include/rte_common.h
> index 573bf4f2ce..51a2eaf8b4 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -121,6 +121,12 @@ extern "C" {
>  #define __rte_aligned(a) __attribute__((__aligned__(a)))
>  #endif
>=20
> +#ifdef RTE_TOOLCHAIN_MSVC
> +#define __rte_assume_aligned(ptr, align) (ptr)
> +#else
> +#define __rte_assume_aligned __builtin_assume_aligned
> +#endif

The GCC/Clang macro supports the optional 3rd parameter (offset), but =
the MSVC doesn't.
Maybe it's better to pass (ptr, align) to the GCC/Clang variant, so the =
API consistently only supports two parameters.

If the 3rd parameter ever becomes needed, it can be implemented as a new =
macro.

Also, a short description of the macro would be nice.


Did you look into using e.g. __rte_assume((ptr % 16) =3D=3D 0) instead?
It's relevant if it has the desired effect for MSVC, which the macro in =
this patch doesn't.