[PATCH] RTC: rtc_time_to_tm: use unsigned arithmetic

[PATCH] RTC: rtc_time_to_tm: use unsigned arithmetic

[Maciej W. Rozycki]

 The input argument to rtc_time_to_tm() is unsigned as well as are members
of the output structure.  However signed arithmetic is used within for
calculations leading to incorrect results for input values outside the
signed positive range.  If this happens the time of day returned is out of
range.

 Found the problem when fiddling with the RTC and the driver where year
was set to an unexpectedly large value like 2070, e.g.:

rtc0: setting system clock to 2070-01-01 1193046:71582832:26 UTC (3155760954)

while it should be:

rtc0: setting system clock to 2070-01-01 00:15:54 UTC (3155760954)

Changing types to unsigned fixes the problem.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
---
 Tested on 64-bit MIPS.  Please apply.

  Maciej

patch-2.6.26-rc1-20080505-rtc-time-unsigned-11
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-lib.c linux-2.6.26-rc1-20080505/drivers/rtc/rtc-lib.c
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-lib.c	2007-07-10 04:56:26.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/rtc-lib.c	2008-05-05 02:37:38.000000000 +0000
@@ -51,7 +51,7 @@ EXPORT_SYMBOL(rtc_year_days);
  */
 void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
 {
-	register int days, month, year;
+	register unsigned int days, month, year;
 
 	days = time / 86400;
 	time -= days * 86400;

Re: [PATCH] RTC: rtc_time_to_tm: use unsigned arithmetic

[Dmitri Vorobiev]

Maciej W. Rozycki пишет:
>  The input argument to rtc_time_to_tm() is unsigned as well as are members
> of the output structure.  However signed arithmetic is used within for
> calculations leading to incorrect results for input values outside the
> signed positive range.  If this happens the time of day returned is out of
> range.
> 
>  Found the problem when fiddling with the RTC and the driver where year
> was set to an unexpectedly large value like 2070, e.g.:
> 
> rtc0: setting system clock to 2070-01-01 1193046:71582832:26 UTC (3155760954)
> 
> while it should be:
> 
> rtc0: setting system clock to 2070-01-01 00:15:54 UTC (3155760954)
> 
> Changing types to unsigned fixes the problem.
> 
> Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
> ---
>  Tested on 64-bit MIPS.  Please apply.
> 
>   Maciej
> 
> patch-2.6.26-rc1-20080505-rtc-time-unsigned-11
> diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-lib.c linux-2.6.26-rc1-20080505/drivers/rtc/rtc-lib.c
> --- linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-lib.c	2007-07-10 04:56:26.000000000 +0000
> +++ linux-2.6.26-rc1-20080505/drivers/rtc/rtc-lib.c	2008-05-05 02:37:38.000000000 +0000
> @@ -51,7 +51,7 @@ EXPORT_SYMBOL(rtc_year_days);
>   */
>  void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
>  {
> -	register int days, month, year;
> +	register unsigned int days, month, year;

Does it make any sense to use the `register' keyword nowadays?

Dmitri

Re: [PATCH] RTC: rtc_time_to_tm: use unsigned arithmetic

[Maciej W. Rozycki]

On Wed, 7 May 2008, Dmitri Vorobiev wrote:

> > -	register int days, month, year;
> > +	register unsigned int days, month, year;
> 
> Does it make any sense to use the `register' keyword nowadays?

 It may or may not -- I have not investigated it that thoroughly.  It is
still correct syntax and a valid optimization hint -- I could imagine the
-Os mode utilizing it on some architecture that can do ALU operations on
memory.

  Maciej