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 <[email protected]>
Cc: Andrew Morton <[email protected]> # as an example of what UBSan finds.
Cc: Alessandro Zummo <[email protected]>
Cc: Alexandre Belloni <[email protected]>
Cc: [email protected]
Signed-off-by: Daniel Axtens <[email protected]>
Acked-by: Alexandre Belloni <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>

0 files changed, 0 insertions, 0 deletions