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, 12 insertions, 2 deletions

diff --git a/lib/libc/dlfcn/init.c b/lib/libc/dlfcn/init.c
index 270f54aada5..3df61076dff 100644
--- a/lib/libc/dlfcn/init.c
+++ b/lib/libc/dlfcn/init.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: init.c,v 1.7 2019/06/02 01:03:01 guenther Exp $ */
+/*	$OpenBSD: init.c,v 1.8 2020/07/06 13:33:05 pirofti Exp $ */
 /*
  * Copyright (c) 2014,2015 Philip Guenther <guenther@openbsd.org>
  *
@@ -20,6 +20,7 @@
 
 #include <sys/types.h>
 #include <sys/syscall.h>
+#include <sys/timetc.h>		/* timekeep */
 
 #ifndef PIC
 #include <sys/mman.h>
@@ -45,8 +46,9 @@
 /* XXX should be in an include file shared with csu */
 char	***_csu_finish(char **_argv, char **_envp, void (*_cleanup)(void));
 
-/* provide definition for this */
+/* provide definitions for these */
 int	_pagesize = 0;
+struct timekeep	*_timekeep;
 
 /*
  * In dynamicly linked binaries environ and __progname are overriden by
@@ -105,6 +107,14 @@ _libc_preinit(int argc, char **argv, char **envp, dl_cb_cb *cb)
 			phnum = aux->au_v;
 			break;
 #endif /* !PIC */
+		case AUX_openbsd_timekeep:
+			if (_tc_get_timecount) {
+				_timekeep = (void *)aux->au_v;
+				if (_timekeep &&
+				    _timekeep->tk_version != TK_VERSION)
+					_timekeep = NULL;
+			}
+			break;
 		}
 	}