Re: [PATCH 5.10.y 5.15.y 6.1.y 6.6.y 6.12.y 6.18.y 6.19.y] ARM: clean up the memset64() C wrapper

[Greg KH <greg@kroah.com>]

On Wed, Feb 25, 2026 at 12:35:09PM +0100, Thomas Weißschuh wrote:
> [ Upstream commit b52343d1cb47bb27ca32a3f4952cc2fd3cd165bf ]
> 
> The current logic to split the 64-bit argument into its 32-bit halves is
> byte-order specific and a bit clunky.  Use a union instead which is
> easier to read and works in all cases.
> 
> GCC still generates the same machine code.
> 
> While at it, rename the arguments of the __memset64() prototype to
> actually reflect their semantics.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Reported-by: Ben Hutchings <ben@decadent.org.uk> # for -stable
> Link: https://lore.kernel.org/all/1a11526ae3d8664f705b541b8d6ea57b847b49a8.camel@decadent.org.uk/
> Suggested-by: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/ # for -stable
> Link: https://lore.kernel.org/all/aZonkWMwpbFhzDJq@casper.infradead.org/
> ---
> Hi stable team,
> 
> unfortunately the backports of commit 23ea2a4c7232 ("ARM: 9468/1: fix
> memset64() on big-endian") does not work on 5.10 and 5.15 as
> CONFIG_CPU_LITTLE_ENDIAN does not exist there, effectively breaking memset64()
> on little-endian. Please use this variant instead which always works.
> For consistency I prefer to have it backported to all versions.
> ---
>  arch/arm/include/asm/string.h | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
> index b5ad23acb303..369781ec5511 100644
> --- a/arch/arm/include/asm/string.h
> +++ b/arch/arm/include/asm/string.h
> @@ -33,13 +33,17 @@ static inline void *memset32(uint32_t *p, uint32_t v, __kernel_size_t n)
>  }
>  
>  #define __HAVE_ARCH_MEMSET64
> -extern void *__memset64(uint64_t *, uint32_t low, __kernel_size_t, uint32_t hi);
> +extern void *__memset64(uint64_t *, uint32_t first, __kernel_size_t, uint32_t second);
>  static inline void *memset64(uint64_t *p, uint64_t v, __kernel_size_t n)
>  {
> -	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
> -		return __memset64(p, v, n * 8, v >> 32);
> -	else
> -		return __memset64(p, v >> 32, n * 8, v);
> +	union {
> +		uint64_t val;
> +		struct {
> +			uint32_t first, second;
> +		};
> +	} word = { .val = v };
> +
> +	return __memset64(p, word.first, n * 8, word.second);
>  }
>  
>  #endif
> 
> ---

I don't understand, why is this patch needed at all?  What issue is it
fixing to require this?

thanks,

greg k-h