Re: [PATCH] s390: include: timex: Use macro CLOCK_STORE_SIZE instead of hard code number

[Chen Gang]

Thank you for your work.

In honest, originally, I was not sure whether it would cause bug (do not
know gcc would generic incorrect code for it). :-)

Thanks.

On 01/02/2015 05:46 PM, Heiko Carstens wrote:
> On Thu, Jan 01, 2015 at 10:27:32PM +0800, Chen Gang wrote:
>> For C language, it treats array parameter as a pointer, so sizeof for an
>> array parameter is equal to sizeof for a pointer, which causes compiler
>> warning (with allmodconfig by gcc 5):
>>
>>     CC      arch/s390/kernel/asm-offsets.s
>>   In file included from include/linux/timex.h:65:0,
>>                    from include/linux/sched.h:19,
>>                    from include/linux/kvm_host.h:15,
>>                    from arch/s390/kernel/asm-offsets.c:10:
>>   ./arch/s390/include/asm/timex.h: In function 'get_tod_clock_ext':
>>   ./arch/s390/include/asm/timex.h:76:32: warning: 'sizeof' on array function parameter 'clk' will return size of 'char *' [-Wsizeof-array-argument]
>>     typedef struct { char _[sizeof(clk)]; } addrtype;
>>                                   ^
>>
>> Can use macro CLOCK_STORE_SIZE instead of all related hard code numbers,
>> which also can avoid this warning. And also add a tab to CLOCK_TICK_RATE
>> definition to match coding styles.
>>
>> Signed-off-by: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
> 
> Thanks. I applied the slightly changed version below.
> 
>>From 77e1e6fd8f5ce0d96c035056f9e963ca7d9198b2 Mon Sep 17 00:00:00 2001
> From: Chen Gang <gang.chen@xxxxxxxxxxxxx>
> Date: Thu, 1 Jan 2015 22:27:32 +0800
> Subject: [PATCH] s390/timex: fix get_tod_clock_ext() inline assembly
> 
> For C language, it treats array parameter as a pointer, so sizeof for an
> array parameter is equal to sizeof for a pointer, which causes compiler
> warning (with allmodconfig by gcc 5):
> 
>   ./arch/s390/include/asm/timex.h: In function 'get_tod_clock_ext':
>   ./arch/s390/include/asm/timex.h:76:32: warning: 'sizeof' on array function parameter 'clk' will return size of 'char *' [-Wsizeof-array-argument]
>     typedef struct { char _[sizeof(clk)]; } addrtype;
>                                   ^
> Can use macro CLOCK_STORE_SIZE instead of all related hard code numbers,
> which also can avoid this warning. And also add a tab to CLOCK_TICK_RATE
> definition to match coding styles.
> 
> [heiko.carstens@xxxxxxxxxx]:
> Chen's patch actually fixes a bug within the get_tod_clock_ext() inline assembly
> where we incorrectly tell the compiler that only 8 bytes of memory get changed
> instead of 16 bytes.
> This would allow gcc to generate incorrect code. Right now this doesn't seem to
> be the case.
> Also slightly changed the patch a bit.
> - renamed CLOCK_STORE_SIZE to STORE_CLOCK_SIZE
> - changed get_tod_clock_ext() to receive a char pointer parameter
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
> Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> ---
>  arch/s390/hypfs/hypfs_vm.c    |  2 +-
>  arch/s390/include/asm/timex.h | 10 ++++++----
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/s390/hypfs/hypfs_vm.c b/arch/s390/hypfs/hypfs_vm.c
> index 32040ace00ea..99a3e6b395ab 100644
> --- a/arch/s390/hypfs/hypfs_vm.c
> +++ b/arch/s390/hypfs/hypfs_vm.c
> @@ -231,7 +231,7 @@ failed:
>  struct dbfs_d2fc_hdr {
>  	u64	len;		/* Length of d2fc buffer without header */
>  	u16	version;	/* Version of header */
> -	char	tod_ext[16];	/* TOD clock for d2fc */
> +	char	tod_ext[STORE_CLOCK_SIZE]; /* TOD clock for d2fc */
>  	u64	count;		/* Number of VM guests in d2fc buffer */
>  	char	reserved[30];
>  } __attribute__ ((packed));
> diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
> index 8beee1cceba4..582be106ab4a 100644
> --- a/arch/s390/include/asm/timex.h
> +++ b/arch/s390/include/asm/timex.h
> @@ -67,20 +67,22 @@ static inline void local_tick_enable(unsigned long long comp)
>  	set_clock_comparator(S390_lowcore.clock_comparator);
>  }
>  
> -#define CLOCK_TICK_RATE	1193180 /* Underlying HZ */
> +#define CLOCK_TICK_RATE		1193180 /* Underlying HZ */
> +#define STORE_CLOCK_SIZE	16	/* number of bytes store clock writes */
>  
>  typedef unsigned long long cycles_t;
>  
> -static inline void get_tod_clock_ext(char clk[16])
> +static inline void get_tod_clock_ext(char *clk)
>  {
> -	typedef struct { char _[sizeof(clk)]; } addrtype;
> +	typedef struct { char _[STORE_CLOCK_SIZE]; } addrtype;
>  
>  	asm volatile("stcke %0" : "=Q" (*(addrtype *) clk) : : "cc");
>  }
>  
>  static inline unsigned long long get_tod_clock(void)
>  {
> -	unsigned char clk[16];
> +	unsigned char clk[STORE_CLOCK_SIZE];
> +
>  	get_tod_clock_ext(clk);
>  	return *((unsigned long long *)&clk[1]);
>  }
> 

-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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