linux-kernel - Re: [PATCH v2 12/13] asm-generic: uaccess: 1-byte access is always aligned

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Date:   Sat, 15 May 2021 11:41:13 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Arnd Bergmann <arnd@...nel.org>, linux-arch@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/13] asm-generic: uaccess: 1-byte access is always
 aligned

On 5/14/21 3:01 AM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> With the cleaned up version of asm-generic/unaligned.h,
> there is a warning about the get_user/put_user helpers using
> unaligned access for single-byte variables:
> 
> include/asm-generic/uaccess.h: In function ‘__get_user_fn’:
> include/asm-generic/unaligned.h:13:15: warning: ‘packed’ attribute ignored for field of type ‘u8’ {aka ‘unsigned char’} [-Wattributes]
>   const struct { type x __packed; } *__pptr = (typeof(__pptr))(ptr); \
> 
> Change these to use a direct pointer dereference to avoid the
> warnings.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/asm-generic/uaccess.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
> index 4973328f3c6e..7e903e450659 100644
> --- a/include/asm-generic/uaccess.h
> +++ b/include/asm-generic/uaccess.h
> @@ -19,7 +19,7 @@ __get_user_fn(size_t size, const void __user *from, void *to)
>  
>  	switch (size) {
>  	case 1:
> -		*(u8 *)to = get_unaligned((u8 __force *)from);
> +		*(u8 *)to = *((u8 __force *)from);
>  		return 0;
>  	case 2:
>  		*(u16 *)to = get_unaligned((u16 __force *)from);
> @@ -45,7 +45,7 @@ __put_user_fn(size_t size, void __user *to, void *from)
>  
>  	switch (size) {
>  	case 1:
> -		put_unaligned(*(u8 *)from, (u8 __force *)to);
> +		*(*(u8 *)from, (u8 __force *)to);

Should that be           from = 
?

>  		return 0;
>  	case 2:
>  		put_unaligned(*(u16 *)from, (u16 __force *)to);
> 


-- 
~Randy