[DTrace-devel] [PATCH] 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."

Change the attach() function so that, if the event_id has not
yet been set, there is an attempt to set it.  This is how the
dtrace and fbt providers behave.

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_prov_sdt.c            |  2 ++
 test/unittest/syscall/tst.entry.sh | 50 ++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100755 test/unittest/syscall/tst.entry.sh

diff --git a/libdtrace/dt_prov_sdt.c b/libdtrace/dt_prov_sdt.c
index 4b2ac31b..1414bdf3 100644
--- a/libdtrace/dt_prov_sdt.c
+++ b/libdtrace/dt_prov_sdt.c
@@ -71,6 +71,8 @@ int tp_attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
 {
 	tp_probe_t	*datap = prp->prv_data;
 
+	if (datap->event_id == -1)
+		prp->prov->impl->probe_info(dtp, prp, NULL, NULL);
 	if (datap->event_id == -1)
 		return 0;
 
diff --git a/test/unittest/syscall/tst.entry.sh b/test/unittest/syscall/tst.entry.sh
new file mode 100755
index 00000000..fc14f7cc
--- /dev/null
+++ b/test/unittest/syscall/tst.entry.sh
@@ -0,0 +1,50 @@
+#!/bin/bash
+#
+# 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.
+
+# Check that syscall:::entry picks up open*:entry.
+
+dtrace=$1
+
+DIRNAME="$tmpdir/entry.$$.$RANDOM"
+mkdir -p $DIRNAME
+cd $DIRNAME
+
+cat > main.c << EOF
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+int main(int c, char **v) {
+    while (open("/dummy/path", O_RDWR) == -1) sleep(1);
+    return 0;
+}
+EOF
+
+gcc main.c
+if [ $? -ne 0 ]; then
+    echo ERROR: compilation failed
+    cat main.c
+    exit 1
+fi
+
+./a.out &
+pid=$!
+
+$dtrace $dt_flags -o tmp.log -n 'syscall:::entry /pid == '$pid'/ {}  tick-5s {exit(0)}'
+if [ $? -ne 0 ]; then
+    echo ERROR: dtrace failed
+    exit 1
+fi
+
+kill %1
+
+if [ `grep -c '^ *open.*:entry *$' tmp.log` -lt 4 ]; then
+    echo ERROR: insufficient probe firings
+    cat tmp.log
+    exit 1
+fi
+
+exit 0
-- 
2.18.4