[PATCH bpf v3 2/2] selftests/bpf: cover UTF-8 trace_printk output

Yihan Ding
2026-04-16T12:04:24Z

Extend trace_printk coverage to verify that UTF-8 literal text is
emitted successfully and that '%' parsing still rejects non-ASCII
bytes once format parsing starts.

Use an explicitly invalid format string for the negative case so the
ASCII-only parser expectation is visible from the test code itself.

Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
---
.../selftests/bpf/prog_tests/trace_printk.c | 28 +++++++++++++++----
.../selftests/bpf/progs/trace_printk.c | 10 +++++++
2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/trace_printk.c b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
index e56e88596d64..a5a8104c1ddd 100644
--- a/tools/testing/selftests/bpf/prog_tests/trace_printk.c
+++ b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
@@ -6,18 +6,21 @@
#include "trace_printk.lskel.h"

#define SEARCHMSG "testing,testing"
+#define SEARCHMSG_UTF8 "中文,测试"

static void trace_pipe_cb(const char *str, void *data)
{
if (strstr(str, SEARCHMSG) != NULL)
- (*(int *)data)++;
+ ((int *)data)[0]++;
+ if (strstr(str, SEARCHMSG_UTF8))
+ ((int *)data)[1]++;
}

void serial_test_trace_printk(void)
{
struct trace_printk_lskel__bss *bss;
struct trace_printk_lskel *skel;
- int err = 0, found = 0;
+ int err = 0, found[2] = {};

skel = trace_printk_lskel__open();
if (!ASSERT_OK_PTR(skel, "trace_printk__open"))
@@ -46,11 +49,24 @@ void serial_test_trace_printk(void)
if (!ASSERT_GT(bss->trace_printk_ret, 0, "bss->trace_printk_ret"))
goto cleanup;

- /* verify our search string is in the trace buffer */
- ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, &found, 1000),
- "read_trace_pipe_iter");
+ if (!ASSERT_GT(bss->trace_printk_utf8_ran, 0, "bss->trace_printk_utf8_ran"))
+ goto cleanup;
+
+ if (!ASSERT_GT(bss->trace_printk_utf8_ret, 0, "bss->trace_printk_utf8_ret"))
+ goto cleanup;
+
+ if (!ASSERT_LT(bss->trace_printk_invalid_spec_ret, 0,
+ "bss->trace_printk_invalid_spec_ret"))
+ goto cleanup;
+
+ /* verify our search strings are in the trace buffer */
+ ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, found, 1000),
+ "read_trace_pipe_iter");
+
+ if (!ASSERT_EQ(found[0], bss->trace_printk_ran, "found"))
+ goto cleanup;

- if (!ASSERT_EQ(found, bss->trace_printk_ran, "found"))
+ if (!ASSERT_EQ(found[1], bss->trace_printk_utf8_ran, "found_utf8"))
goto cleanup;

cleanup:
diff --git a/tools/testing/selftests/bpf/progs/trace_printk.c b/tools/testing/selftests/bpf/progs/trace_printk.c
index 6695478c2b25..f4c538ec3ebd 100644
--- a/tools/testing/selftests/bpf/progs/trace_printk.c
+++ b/tools/testing/selftests/bpf/progs/trace_printk.c
@@ -10,13 +10,23 @@ char _license[] SEC("license") = "GPL";

int trace_printk_ret = 0;
int trace_printk_ran = 0;
+int trace_printk_invalid_spec_ret = 0;
+int trace_printk_utf8_ret = 0;
+int trace_printk_utf8_ran = 0;

const char fmt[] = "Testing,testing %d\n";
+static const char utf8_fmt[] = "中文,测试 %d\n";
+/* Non-ASCII bytes after '%' must still be rejected. */
+static const char invalid_spec_fmt[] = "%\x80\n";

SEC("fentry/" SYS_PREFIX "sys_nanosleep")
int sys_enter(void *ctx)
{
trace_printk_ret = bpf_trace_printk(fmt, sizeof(fmt),
++trace_printk_ran);
+ trace_printk_utf8_ret = bpf_trace_printk(utf8_fmt, sizeof(utf8_fmt),
+ ++trace_printk_utf8_ran);
+ trace_printk_invalid_spec_ret = bpf_trace_printk(invalid_spec_fmt,
+ sizeof(invalid_spec_fmt));
return 0;
}
--
2.20.1