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Date: Thu, 15 Feb 2024 16:33:45 -0800
From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org, Morten =?iso-8859-1?Q?Br=F8rup?= <mb@smartsharesystems.com>
Subject: Re: [PATCH v2 3/3] eal: replace out of bounds VLA with static_assert
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References: <20231111172153.57461-1-stephen@networkplumber.org>
 <20231113170605.408281-1-stephen@networkplumber.org>
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ping

i'd like to see this change go in asap since it is pre-requisite to
turning on -Wvla which explicitly caught use of non-constant expressions
in the RTE_BUILD_BUG_ON() hiding bugs.

thanks!

On Mon, Nov 13, 2023 at 09:06:05AM -0800, Stephen Hemminger wrote:
> Both Gcc, clang and MSVC have better way to do compile time
> assertions rather than using out of bounds array access.
> The old method would fail if -Wvla is enabled because compiler
> can't determine size in that code.  Also, the use of new
> _Static_assert will catch broken code that is passing non-constant
> expression to RTE_BUILD_BUG_ON().
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> ---
>  lib/eal/include/rte_common.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
> index c1ba32d00e47..bea7c0e57d5e 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -16,6 +16,7 @@
>  extern "C" {
>  #endif
>  
> +#include <assert.h>
>  #include <stdint.h>
>  #include <limits.h>
>  
> @@ -495,7 +496,7 @@ rte_is_aligned(const void * const __rte_restrict ptr, const unsigned int align)
>  /**
>   * Triggers an error at compilation time if the condition is true.
>   */
> -#define RTE_BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
> +#define RTE_BUILD_BUG_ON(condition) static_assert(!(condition), #condition)
>  
>  /*********** Cache line related macros ********/
>  
> -- 
> 2.39.2