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Subject: Re: [PATCH] [RESEND] ARM: sharpsl_param: work around
 -Wstringop-overread warning
To:     Arnd Bergmann <arnd@kernel.org>, soc@kernel.org
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Haojian Zhuang <haojian.zhuang@gmail.com>,
        Robert Jarzmik <robert.jarzmik@free.fr>,
        Russell King <linux@armlinux.org.uk>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20210927145332.2784005-1-arnd@kernel.org>
From:   Daniel Mack <daniel@zonque.org>
Message-ID: <413f2684-f818-4d0b-bf7c-142f55b3737f@zonque.org>
Date:   Mon, 27 Sep 2021 16:55:13 +0200
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On 9/27/21 4:53 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> gcc warns that accessing a pointer based on a numeric constant may
> be an offset into a NULL pointer, and would therefore has zero
> accessible bytes:
> 
> arch/arm/common/sharpsl_param.c: In function ‘sharpsl_save_param’:
> arch/arm/common/sharpsl_param.c:43:9: error: ‘memcpy’ reading 64 bytes from a region of size 0 [-Werror=stringop-overread]
>    43 |         memcpy(&sharpsl_param, param_start(PARAM_BASE), sizeof(struct sharpsl_param_info));
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> In this particular case, the warning is bogus since this is the actual
> pointer, not an offset on a NULL pointer. Add a local variable to shut
> up the warning and hope it doesn't come back.
> 
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578

Acked-by: Daniel Mack <daniel@zonque.org>


> Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
> Cc: Robert Jarzmik <robert.jarzmik@free.fr>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> If there are no objections, I'd apply this one through the soc tree.
> ---
>  arch/arm/common/sharpsl_param.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/common/sharpsl_param.c b/arch/arm/common/sharpsl_param.c
> index efeb5724d9e9..6237ede2f0c7 100644
> --- a/arch/arm/common/sharpsl_param.c
> +++ b/arch/arm/common/sharpsl_param.c
> @@ -40,7 +40,9 @@ EXPORT_SYMBOL(sharpsl_param);
>  
>  void sharpsl_save_param(void)
>  {
> -	memcpy(&sharpsl_param, param_start(PARAM_BASE), sizeof(struct sharpsl_param_info));
> +	struct sharpsl_param_info *params = param_start(PARAM_BASE);
> +
> +	memcpy(&sharpsl_param, params, sizeof(*params));
>  
>  	if (sharpsl_param.comadj_keyword != COMADJ_MAGIC)
>  		sharpsl_param.comadj=-1;
>