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author | Daniel Axtens <dja@axtens.net> | 2015-12-15 18:09:14 +1100 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2015-12-16 12:54:04 +1100 |
commit | 00b912b0c88e690b1662067497182454357b18b0 (patch) | |
tree | 1e6f6ab3201f4078645d5351c9a2721c4aedf54c /arch/powerpc/kernel/time.c | |
parent | 5f337e3e5b04b32793fd51adab438d46df99c933 (diff) | |
download | blackbird-op-linux-00b912b0c88e690b1662067497182454357b18b0.tar.gz blackbird-op-linux-00b912b0c88e690b1662067497182454357b18b0.zip |
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>
Diffstat (limited to 'arch/powerpc/kernel/time.c')
-rw-r--r-- | arch/powerpc/kernel/time.c | 36 |
1 files changed, 2 insertions, 34 deletions
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 1be1092c7204..81b0900a39ee 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -1002,38 +1002,6 @@ static int month_days[12] = { 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 @@ void to_tm(int tim, struct rtc_time * tm) 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); |