[DTrace-devel] [PATCH v2 4/7] trace: handle the empty string in a sensible way

[Kris Van Hees]

The trace("") action would dump a series of 0x00 bytes (strsize of
them) rather than printing an empty string.  While that is the legacy
behaviour, it does not really make any sense to do so.  The trace
action is described as printing data as a string if possible, and a
block of 0-bytes can certainly be printed as an empty string.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_consume.c                      |  2 +-
 test/unittest/actions/trace/tst.str-empty.d | 18 ++++++++++++++++++
 test/unittest/actions/trace/tst.str-empty.r |  5 +++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 test/unittest/actions/trace/tst.str-empty.d
 create mode 100644 test/unittest/actions/trace/tst.str-empty.r

diff --git a/libdtrace/dt_consume.c b/libdtrace/dt_consume.c
index edfe5bbae..2dce69d6d 100644
--- a/libdtrace/dt_consume.c
+++ b/libdtrace/dt_consume.c
@@ -991,7 +991,7 @@ dt_print_bytes(dtrace_hdl_t *dtp, FILE *fp, caddr_t addr,
 		    c[i] == '\b' || c[i] == '\a')
 			continue;
 
-		if (c[i] == '\0' && i > 0) {
+		if (c[i] == '\0') {
 			/*
 			 * This looks like it might be a string.  Before we
 			 * assume that it is indeed a string, check the
diff --git a/test/unittest/actions/trace/tst.str-empty.d b/test/unittest/actions/trace/tst.str-empty.d
new file mode 100644
index 000000000..38fcb8857
--- /dev/null
+++ b/test/unittest/actions/trace/tst.str-empty.d
@@ -0,0 +1,18 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2025, 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.
+ */
+
+/*
+ * ASSERTION: The trace() action prints an empty string value correctly.
+ *
+ * SECTION: Actions and Subroutines/trace()
+ */
+
+BEGIN
+{
+	trace("");
+	exit(0);
+}
diff --git a/test/unittest/actions/trace/tst.str-empty.r b/test/unittest/actions/trace/tst.str-empty.r
new file mode 100644
index 000000000..8c15aa7f5
--- /dev/null
+++ b/test/unittest/actions/trace/tst.str-empty.r
@@ -0,0 +1,5 @@
+                   FUNCTION:NAME
+                          :BEGIN                                    
+
+-- @@stderr --
+dtrace: script 'test/unittest/actions/trace/tst.str-empty.d' matched 1 probe
-- 
2.45.2