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, 2 insertions, 2 deletions

diff --git a/lib/libc/gen/time.c b/lib/libc/gen/time.c
index 3bbd0d733d1..7e24d60f6cb 100644
--- a/lib/libc/gen/time.c
+++ b/lib/libc/gen/time.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: time.c,v 1.8 2019/06/28 13:32:41 deraadt Exp $ */
+/*	$OpenBSD: time.c,v 1.9 2020/07/06 13:33:06 pirofti Exp $ */
 /*
  * Copyright (c) 1983, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -36,7 +36,7 @@ time(time_t *t)
 {
 	struct timeval tt;
 
-	if (gettimeofday(&tt, NULL) == -1)
+	if (WRAP(gettimeofday)(&tt, NULL) == -1)
 		return (-1);
 	if (t)
 		*t = (time_t)tt.tv_sec;