On Wed, 14 Dec 2016, Guenter Roeck wrote:
> avr32:allnoconfig:
>
> kernel/built-in.o: In function `do_adjtimex':
> (.text+0x1d748): undefined reference to `posix_timer_event'
> make[1]: *** [vmlinux] Error 1
>
> metag:allnoconfig:
>
> kernel/built-in.o: In function `alarm_handle_timer':
> alarmtimer.c:(.text.alarm_handle_timer+0x38): undefined reference to
> `posix_timer_event'
>
> openrisc:allnoconfig:
>
> kernel/built-in.o: In function `alarm_handle_timer':
> alarmtimer.c:(.text+0x3fca4): undefined reference to `posix_timer_event'
>
> unicore32:allnoconfig:
>
> kernel/built-in.o: In function `alarm_handle_timer':
> memremap.c:(.text+0x31c1c): undefined reference to `posix_timer_event'
>
> Since I don't run allnoconfig builds for all architectures, I strongly suspect
> that more are affected.
This is a known problem. Oddly enough only those "less popular"
architectures are affected.
> Looking into alarmtimer.c, with seems to call posix_timer_event()
> unconditionally, I don't entirely understand how this can work in the
> first place. Maybe I am missing something, though.
The magic is in alarmtimer_init():
if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
posix_timers_register_clock(CLOCK_REALTIME_ALARM, &alarm_clock);
posix_timers_register_clock(CLOCK_BOOTTIME_ALARM, &alarm_clock);
}
If CONFIG_POSIX_TIMERS is not enabled, the condition becomes a constant
zero. The posix_timers_register_clock calls are then optimized away by
the compiler. In turn the alarm_clock structure has no longer any
reference to it and therefore is also optimized away, including its
method functions such as alarm_timer_create() and finally
alarm_handle_timer().
But for some reasons, some gcc versions (mainly for "secondary"
architectures) fail to optimize away all that code, and a dead reference
to posix_timer_event() remains in the compiled code.
There is a fix already queued in the mm tree. It goes like this:
posix-timers: give lazy compilers some help optimizing code away
The OpenRISC compiler (so far) fails to optimize away a large portion
of code containing a reference to posix_timer_event in alarmtimer.c when
CONFIG_POSIX_TIMERS is unset. Let's give it a direct clue to let the build
succeed.
This fixes
[linux-next:master 6682/7183] alarmtimer.c:undefined reference to
`posix_timer_event'
reported by kbuild test robot.
Signed-off-by: Nicolas Pitre <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Josh Triplett <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 9b08ca391a..3921cf7fea 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -516,7 +516,8 @@ static enum alarmtimer_restart alarm_handle_timer(struct
alarm *alarm,
spin_lock_irqsave(&ptr->it_lock, flags);
if ((ptr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) {
- if (posix_timer_event(ptr, 0) != 0)
+ if (IS_ENABLED(CONFIG_POSIX_TIMERS) &&
+ posix_timer_event(ptr, 0) != 0)
ptr->it_overrun++;
}
