linux-kernel - Re: [PATCH] mpis: cavium-octeon/executive/cvmx-l2c.c: fix uninitialized variable

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Message-ID: <50F6E9B3.5010202@caviumnetworks.com>
Date:	Wed, 16 Jan 2013 09:56:03 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	Cong Ding <dinggnu@...il.com>, Jim Quinlan <jim2101024@...il.com>,
	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mpis: cavium-octeon/executive/cvmx-l2c.c: fix uninitialized
 variable

On 01/16/2013 02:57 AM, Ralf Baechle wrote:
> On Mon, Jan 14, 2013 at 10:47:03PM +0100, Cong Ding wrote:
>
>> the variable dummy is used without initialization.
>
> Interesting - I wonder how you found this one.  My compiler (gcc 4.7)
> doesn't warn about this one.
>

I get no warnings either.  So I wonder what the point of churning up the 
code is.

David Daney

> Nor does gcc notice that the whole summing up business is wasted efford.
>
> So here's my counter proposal.  It works because ptr is a volatile pointer
> so the compiler will always dereference it even if the returned value is
> not being used.  The resulting code is a bit smaller.
>
>    Ralf
>
> Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
>
>   arch/mips/cavium-octeon/executive/cvmx-l2c.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/mips/cavium-octeon/executive/cvmx-l2c.c b/arch/mips/cavium-octeon/executive/cvmx-l2c.c
> index 9f883bf..ec3e059 100644
> --- a/arch/mips/cavium-octeon/executive/cvmx-l2c.c
> +++ b/arch/mips/cavium-octeon/executive/cvmx-l2c.c
> @@ -286,7 +286,7 @@ uint64_t cvmx_l2c_read_perf(uint32_t counter)
>   static void fault_in(uint64_t addr, int len)
>   {
>   	volatile char *ptr;
> -	volatile char dummy;
> +
>   	/*
>   	 * Adjust addr and length so we get all cache lines even for
>   	 * small ranges spanning two cache lines.
> @@ -300,7 +300,7 @@ static void fault_in(uint64_t addr, int len)
>   	 */
>   	CVMX_DCACHE_INVALIDATE;
>   	while (len > 0) {
> -		dummy += *ptr;
> +		*ptr;
>   		len -= CVMX_CACHE_LINE_SIZE;
>   		ptr += CVMX_CACHE_LINE_SIZE;
>   	}
>
>
>


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