RE: [RFC] eal/x86: disable array bounds checks in rte_memcpy_generic with gcc-12

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Thursday, 9 June 2022 00.49
> 
> Gcc 12 adds more array bounds checking (good); but it is not smart
> enough to realize that for small fixed sizes, the bigger move options
> are not used.
> 
> An example is using rte_memcpy() on a RSS key of 40 bytes may trigger
> rte_memcpy complaints from rte_mov128 reading past end of input.
> 
> In order to keep some of the checks add special case for calls
> to rte_memcpy() with fixed size arguments to use the compiler
> builtin instead. Don't want to give all the checking for
> code that uses rte_memcpy() everywhere.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  lib/eal/x86/include/rte_memcpy.h | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/eal/x86/include/rte_memcpy.h
> b/lib/eal/x86/include/rte_memcpy.h
> index 18aa4e43a743..b90cdd8d7326 100644
> --- a/lib/eal/x86/include/rte_memcpy.h
> +++ b/lib/eal/x86/include/rte_memcpy.h
> @@ -27,6 +27,10 @@ extern "C" {
>  #pragma GCC diagnostic ignored "-Wstringop-overflow"
>  #endif
> 
> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 120000)
> +#pragma GCC diagnostic ignored "-Warray-bounds"
> +#endif
> +
>  /**
>   * Copy bytes from one location to another. The locations must not
> overlap.
>   *
> @@ -842,19 +846,21 @@ rte_memcpy_aligned(void *dst, const void *src,
> size_t n)
>  	return ret;
>  }
> 
> +#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
> +#pragma GCC diagnostic pop
> +#endif
> +
>  static __rte_always_inline void *
>  rte_memcpy(void *dst, const void *src, size_t n)
>  {
> -	if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK))
> +	if (__builtin_constant_p(n))
> +		return __builtin_memcpy(dst, src, n);
> +	else if (!(((uintptr_t)dst | (uintptr_t)src) & ALIGNMENT_MASK))
>  		return rte_memcpy_aligned(dst, src, n);
>  	else
>  		return rte_memcpy_generic(dst, src, n);
>  }
> 
> -#if defined(RTE_TOOLCHAIN_GCC) && (GCC_VERSION >= 100000)
> -#pragma GCC diagnostic pop
> -#endif
> -
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 2.35.1
> 

Very good.

Reviewed-by: Morten Brørup <mb@smartsharesystems.com>

While you are at it, would you consider concealing the definition of ALIGNMENT_MASK too? It seems to be leaking out from this header file.