Add support for built-in variable walltimestamp

In the pre-compiled function get_bvar(), use bpf_ktime_get_ns() to
get the time (in nsec) since boot.  This value is adjusted by adding
the POSIX time when the system was booted.

A few more walltimestamp tests pass now, but existing walltimestamp
tests are rather lenient.  Add a new, more stringent test.  In particular,
timestamp is supposed to be fixed for an entire clause while walltimestamp
is fresh with every call.

Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

bpf/get_bvar.c

@@ -27,6 +27,7 @@ extern struct bpf_map_def state;
 extern uint64_t STBSZ;
 extern uint64_t STKOFF;
 extern uint64_t STKSIZ;
+extern uint64_t BOOTTM;
 
 #define error(dctx, fault, illval) \
 	({ \
@@ -134,6 +135,8 @@ noinline uint64_t dt_get_bvar(dt_dctx_t *dctx, uint32_t id)
 
 		return val & 0x00000000ffffffffUL;
 	}
+	case DIF_VAR_WALLTIMESTAMP:
+		return bpf_ktime_get_ns() + ((uint64_t)&BOOTTM);
 	case DIF_VAR_PPID: {
 		uint64_t	ptr;
 		int32_t		val = -1;

libdtrace/dt_bpf.h

@@ -25,6 +25,7 @@ extern "C" {
 #define DT_CONST_STBSZ	5
 #define DT_CONST_STKOFF	6
 #define DT_CONST_STKSIZ	7
+#define DT_CONST_BOOTTM	8
 
 extern int perf_event_open(struct perf_event_attr *attr, pid_t pid, int cpu,
 			   int group_fd, unsigned long flags);

libdtrace/dt_cc.c

@@ -2215,6 +2215,20 @@ dt_link_layout(dtrace_hdl_t *dtp, const dtrace_difo_t *dp, uint_t *pcp,
 	return pc;
 }
 
+static uint64_t boottime = 0;
+static int get_boottime() {
+	struct timespec t_real, t_boot;
+
+	if (clock_gettime(CLOCK_REALTIME, &t_real))
+		return -1;
+	if (clock_gettime(CLOCK_MONOTONIC, &t_boot))
+		return -1;
+	boottime = t_real.tv_sec - t_boot.tv_sec;
+	boottime *= 1000000000;
+	boottime += t_real.tv_nsec - t_boot.tv_nsec;
+	return 0;
+}
+
 static int
 dt_link_construct(dtrace_hdl_t *dtp, const dt_probe_t *prp, dtrace_difo_t *dp,
 		  dt_ident_t *idp, const dtrace_difo_t *sdp, dt_strtab_t *stab,
@@ -2338,6 +2352,11 @@ dt_link_construct(dtrace_hdl_t *dtp, const dt_probe_t *prp, dtrace_difo_t *dp,
 				nrp->dofr_data = sizeof(uint64_t)
 				    * dtp->dt_options[DTRACEOPT_MAXFRAMES];
 				continue;
+			case DT_CONST_BOOTTM:
+				if (boottime == 0 && get_boottime())
+					return -1;
+				nrp->dofr_data = boottime;
+				continue;
 			default:
 				/* probe name -> value is probe id */
 				if (strchr(idp->di_name, ':') != NULL)

libdtrace/dt_dlibs.c

@@ -80,6 +80,7 @@ static const dt_ident_t		dt_bpf_symbols[] = {
 	DT_BPF_SYMBOL_ID(STBSZ, DT_IDENT_SCALAR, DT_CONST_STBSZ),
 	DT_BPF_SYMBOL_ID(STKOFF, DT_IDENT_SCALAR, DT_CONST_STKOFF),
 	DT_BPF_SYMBOL_ID(STKSIZ, DT_IDENT_SCALAR, DT_CONST_STKSIZ),
+	DT_BPF_SYMBOL_ID(BOOTTM, DT_IDENT_SCALAR, DT_CONST_BOOTTM),
 	/* End-of-list marker */
 	{ NULL, }
 };

test/demo/act/time.d

@@ -1,11 +1,10 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2005, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  */
 
-/* @@xfail: dtv2 */
 /* @@trigger: none */
 
 #pragma D option quiet

test/unittest/printa/tst.walltimestamp.sh

@@ -5,7 +5,7 @@
 # Licensed under the Universal Permissive License v 1.0 as shown at
 # http://oss.oracle.com/licenses/upl.
 #
-# @@xfail: dtv2
+
 if [ $# != 1 ]; then
 	echo expected one argument: '<'dtrace-path'>'
 	exit 2

test/unittest/variables/bvar/tst.walltimestamp.d

@@ -4,7 +4,6 @@
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  */
-/* @@xfail: dtv2 */
 
 /*
  * ASSERTION: The 'walltimestamp' variable can be accessed and is not -1.

test/unittest/variables/bvar/tst.walltimestamp2.d

@@ -0,0 +1,29 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+#pragma D option quiet
+#pragma D option destructive
+
+BEGIN {
+	/* baseline time stamp from system("date") */
+	system("date +'%%s.%%N'");
+
+	/* get five consecutive time stamps from DTrace */
+	t1 = walltimestamp;
+	t2 = walltimestamp;
+	t3 = walltimestamp;
+	t4 = walltimestamp;
+	t5 = walltimestamp;
+
+	/* report the first time stamp and the subsequent deltas */
+	printf("%d\n", t1);
+	printf("%d\n", t2 - t1);
+	printf("%d\n", t3 - t2);
+	printf("%d\n", t4 - t3);
+	printf("%d\n", t5 - t4);
+	exit(0);
+}

test/unittest/variables/bvar/tst.walltimestamp2.r

@@ -0,0 +1 @@
+success

test/unittest/variables/bvar/tst.walltimestamp2.r.p

@@ -0,0 +1,40 @@
+#!/usr/bin/gawk -f
+#
+# Oracle Linux DTrace.
+# Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+# Licensed under the Universal Permissive License v 1.0 as shown at
+# http://oss.oracle.com/licenses/upl.
+
+{
+        # read the value generated by system("date")
+        t0 = $1; getline;
+
+        # read a walltimestamp value from DTrace
+        t1 = $1; getline;
+
+        # read a few walltimestamp deltas from DTrace
+        d2 = $1; getline;
+        d3 = $1; getline;
+        d4 = $1; getline;
+        d5 = $1;
+
+        # check that the deltas are all positive
+        if (d2 <= 0 ||
+            d3 <= 0 ||
+            d4 <= 0 ||
+            d5 <= 0) print "ERROR: walltimestamp did not advance.";
+
+        # check that the deltas are all under 0.2 seconds
+        if (d2 > 200000000 ||
+            d3 > 200000000 ||
+            d4 > 200000000 ||
+            d5 > 200000000) print "ERROR: walltimestamp delta is high.";
+
+        # check walltimestamp against system("date")
+        t_error = 1.e-9 * t1 - t0;
+        if (t_error < 0) t_error *= -1;
+        if (t_error > 0.2) print "ERROR: walltimestamp and system(date) disagree.";
+
+        print "success";
+        exit 0;
+}