powerpc: Remove broken GregorianDay()
GregorianDay() is supposed to calculate the day of the week
(tm->tm_wday) for a given day/month/year. In that calcuation it
indexed into an array called MonthOffset using tm->tm_mon-1. However
tm_mon is zero-based, not one-based, so this is off-by-one. It also
means that every January, GregoiranDay() will access element -1 of
the MonthOffset array.
It also doesn't appear to be a correct algorithm either: see in
contrast kernel/time/timeconv.c's time_to_tm function.
It's been broken forever, which suggests no-one in userland uses
this. It looks like no-one in the kernel uses tm->tm_wday either
(see e.g. drivers/rtc/rtc-ds1305.c:319).
tm->tm_wday is conventionally set to -1 when not available in
hardware so we can simply set it to -1 and drop the function.
(There are over a dozen other drivers in drivers/rtc that do
this.)
Found using UBSAN.
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org> # as an example of what UBSan finds.
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 1be1092..81b0900 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -1002,38 +1002,6 @@
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};
-/*
- * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
- */
-void GregorianDay(struct rtc_time * tm)
-{
- int leapsToDate;
- int lastYear;
- int day;
- int MonthOffset[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
-
- lastYear = tm->tm_year - 1;
-
- /*
- * Number of leap corrections to apply up to end of last year
- */
- leapsToDate = lastYear / 4 - lastYear / 100 + lastYear / 400;
-
- /*
- * This year is a leap year if it is divisible by 4 except when it is
- * divisible by 100 unless it is divisible by 400
- *
- * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 was
- */
- day = tm->tm_mon > 2 && leapyear(tm->tm_year);
-
- day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] +
- tm->tm_mday;
-
- tm->tm_wday = day % 7;
-}
-EXPORT_SYMBOL_GPL(GregorianDay);
-
void to_tm(int tim, struct rtc_time * tm)
{
register int i;
@@ -1064,9 +1032,9 @@
tm->tm_mday = day + 1;
/*
- * Determine the day of week
+ * No-one uses the day of the week.
*/
- GregorianDay(tm);
+ tm->tm_wday = -1;
}
EXPORT_SYMBOL(to_tm);