Add support for timeconting in userland.

This diff exposes parts of clock_gettime(2) and gettimeofday(2) to
userland via libc eliberating processes from the need for a context
switch everytime they want to count the passage of time.

If a timecounter clock can be exposed to userland than it needs to set
its tc_user member to a non-zero value. Tested with one or multiple
counters per architecture.

The timing data is shared through a pointer found in the new ELF
auxiliary vector AUX_openbsd_timekeep containing timehands information
that is frequently updated by the kernel.

Timing differences between the last kernel update and the current time
are adjusted in userland by the tc_get_timecount() function inside the
MD usertc.c file.

This permits a much more responsive environment, quite visible in
browsers, office programs and gaming (apparently one is are able to fly
in Minecraft now).

Tested by robert@, sthen@, naddy@, kmos@, phessler@, and many others!

OK from at least kettenis@, cheloha@, naddy@, sthen@

1 files changed, 5 insertions, 0 deletions

diff --git a/src/regress/lib/libc/timekeep/Makefile b/src/regress/lib/libc/timekeep/Makefile
new file mode 100644
index 0000000000..ed7dc60379
--- /dev/null
+++ b/src/regress/lib/libc/timekeep/Makefile
@@ -0,0 +1,5 @@
+#       $OpenBSD: Makefile,v 1.1 2020/07/06 13:33:06 pirofti Exp $
+
+PROGS=  test_clock_gettime test_time_skew test_gettimeofday
+
+.include <bsd.regress.mk>