[DTrace-devel] [PATCH v2] sdt and syscall probe descriptions broken when multiple probes

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

The sdt and syscall providers are broken in that, when a probe
description corresponds to multiple probes, a BPF program is
attached to only one of the probes.  E.g., syscall:::entry will
attach a BPF program to only one probe, even though hundreds of
probes are indicated!  The problem is that the attach function
looks for an event_id, skipping the probe if there is no such ID,
but the ID exists for only the "representative probe."

Therefore, call dt_probe_info() when we append probes to the
dt_enablings list.

What is surprising is that, with this fix, there are no XPASS
tests.  That is, there had presumably been no XFAIL tests
("expected fails") that had been failing due *only* to this
problem.  A quick survey of tests suggests that this is likely;
remarkably few tests rely on such functionality, and those that
do still fail due to other missing support (such as strings or
other providers).

Therefore, add a test to check the fix.

Orabug: 32036431
Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_program.c            |  6 +++++-
 test/unittest/syscall/tst.entry.d | 20 ++++++++++++++++++++
 test/unittest/syscall/tst.entry.r |  5 +++++
 3 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 test/unittest/syscall/tst.entry.d
 create mode 100644 test/unittest/syscall/tst.entry.r

diff --git a/libdtrace/dt_program.c b/libdtrace/dt_program.c
index b82cc85c..a5f21617 100644
--- a/libdtrace/dt_program.c
+++ b/libdtrace/dt_program.c
@@ -146,8 +146,12 @@ typedef struct pi_state {
 static int
 dt_stmt_probe(dtrace_hdl_t *dtp, dt_probe_t *prp, pi_state_t *st)
 {
-	if (!dt_in_list(&dtp->dt_enablings, prp))
+	if (!dt_in_list(&dtp->dt_enablings, prp)) {
+		dtrace_probeinfo_t p;
+
+		dt_probe_info(dtp, prp->desc, &p);
 		dt_list_append(&dtp->dt_enablings, prp);
+	}
 
 	dt_probe_add_clause(dtp, prp, st->idp);
 	(*st->cnt)++;
diff --git a/test/unittest/syscall/tst.entry.d b/test/unittest/syscall/tst.entry.d
new file mode 100644
index 00000000..f2d56150
--- /dev/null
+++ b/test/unittest/syscall/tst.entry.d
@@ -0,0 +1,20 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2020, 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.
+ */
+
+/* @@trigger: syscall-tst-args */
+/* @@trigger-timing: before */
+/* @@runtest-opts: $_pid */
+
+/* check that syscall:::entry picks up mmap:entry */
+/* (mmap is called repeatedly by the trigger) */
+/* trigger-timing and runtest-opts are used since -c is not yet supported */
+
+syscall:::entry
+/pid == $1/
+{
+    exit(0);
+}
diff --git a/test/unittest/syscall/tst.entry.r b/test/unittest/syscall/tst.entry.r
new file mode 100644
index 00000000..8066c23f
--- /dev/null
+++ b/test/unittest/syscall/tst.entry.r
@@ -0,0 +1,5 @@
+                   FUNCTION:NAME
+                      mmap:entry 
+
+-- @@stderr --
+dtrace: script 'test/unittest/syscall/tst.entry.d' matched 333 probes
-- 
2.18.4