linux-kernel - Re: [PATCH] mtd: sm_ftl: fix NULL pointer warning

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Date:   Wed, 8 Jan 2020 09:15:28 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Wenwen Wang <wenwen@...uga.edu>, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: sm_ftl: fix NULL pointer warning

Hi Arnd,

Arnd Bergmann <arnd@...db.de> wrote on Tue,  7 Jan 2020 22:24:52 +0100:

> With gcc -O3, we get a new warning:
> 
> In file included from arch/arm64/include/asm/processor.h:28,
>                  from drivers/mtd/sm_ftl.c:8:
> In function 'memset',
>     inlined from 'sm_read_sector.constprop' at drivers/mtd/sm_ftl.c:250:3:
> include/linux/string.h:411:9: error: argument 1 null where non-null expected [-Werror=nonnull]
>   return __builtin_memset(p, c, size);
> 
> From all I can tell, this cannot happen (the function is called
> either with a NULL buffer or with a -1 block number but not both),
> but adding a check makes it more robust and avoids the warning.
> 
> Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/mtd/sm_ftl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/sm_ftl.c b/drivers/mtd/sm_ftl.c
> index 4744bf94ad9a..b9f272408c4d 100644
> --- a/drivers/mtd/sm_ftl.c
> +++ b/drivers/mtd/sm_ftl.c
> @@ -247,7 +247,8 @@ static int sm_read_sector(struct sm_ftl *ftl,
>  
>  	/* FTL can contain -1 entries that are by default filled with bits */
>  	if (block == -1) {
> -		memset(buffer, 0xFF, SM_SECTOR_SIZE);
> +		if (buffer)
> +			memset(buffer, 0xFF, SM_SECTOR_SIZE);
>  		return 0;
>  	}
>  

What about a simpler form:

        if (buffer && block == -1) { ...

Instead of an additional indentation level? 

Thanks,
Miquèl