[PATCH v5 11/14] eal: expand most macros to empty when using MSVC

[Morten Brørup]

> From: Tyler Retzlaff [mailto:roretzla at linux.microsoft.com]
> Sent: Thursday, 13 April 2023 23.26
> 
> For now expand a lot of common rte macros empty. The catch here is we
> need to test that most of the macros do what they should but at the same
> time they are blocking work needed to bootstrap of the unit tests.
> 
> Later we will return and provide (where possible) expansions that work
> correctly for msvc and where not possible provide some alternate macros
> to achieve the same outcome.
> 
> Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> ---
>  lib/eal/include/rte_branch_prediction.h |  8 ++++++
>  lib/eal/include/rte_common.h            | 45
> +++++++++++++++++++++++++++++++++
>  lib/eal/include/rte_compat.h            | 20 +++++++++++++++
>  3 files changed, 73 insertions(+)
> 
> diff --git a/lib/eal/include/rte_branch_prediction.h
> b/lib/eal/include/rte_branch_prediction.h
> index 0256a9d..d9a0224 100644
> --- a/lib/eal/include/rte_branch_prediction.h
> +++ b/lib/eal/include/rte_branch_prediction.h
> @@ -25,7 +25,11 @@
>   *
>   */
>  #ifndef likely
> +#ifndef RTE_TOOLCHAIN_MSVC
>  #define likely(x)	__builtin_expect(!!(x), 1)
> +#else
> +#define likely(x)	(x)

This must be (!!(x)), because x may be non-Boolean, e.g. likely(n & 0x10), and likely() must return Boolean (0 or 1).

> +#endif
>  #endif /* likely */
> 
>  /**
> @@ -39,7 +43,11 @@
>   *
>   */
>  #ifndef unlikely
> +#ifndef RTE_TOOLCHAIN_MSVC
>  #define unlikely(x)	__builtin_expect(!!(x), 0)
> +#else
> +#define unlikely(x)	(x)

This must also be (!!(x)), for the same reason as above.

> +#endif
>  #endif /* unlikely */
> 
>  #ifdef __cplusplus
> diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
> index 2f464e3..1bdaa2d 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -65,7 +65,11 @@
>  /**
>   * Force alignment
>   */
> +#ifndef RTE_TOOLCHAIN_MSVC
>  #define __rte_aligned(a) __attribute__((__aligned__(a)))
> +#else
> +#define __rte_aligned(a)
> +#endif

It should be reviewed that __rte_aligned() is only used for optimization purposes, and is not required for DPDK to function properly.

> 
>  #ifdef RTE_ARCH_STRICT_ALIGN
>  typedef uint64_t unaligned_uint64_t __rte_aligned(1);
> @@ -80,16 +84,29 @@
>  /**
>   * Force a structure to be packed
>   */
> +#ifndef RTE_TOOLCHAIN_MSVC
>  #define __rte_packed __attribute__((__packed__))
> +#else
> +#define __rte_packed
> +#endif

Similar comment as for __rte_aligned(); however, I consider it more likely that structure packing is a functional requirement, and not just used for optimization. Based on my experience, it may be used for packing network structures; perhaps not in DPDK itself but maybe in DPDK applications.

The same risk applies to __rte_aligned(), but with lower probability.