selftests/bpf: Add trace_vprintk test prog

This commit adds a test prog for vprintk which confirms that:
  * bpf_trace_vprintk is writing to /sys/kernel/debug/tracing/trace_pipe
  * __bpf_vprintk macro works as expected
  * >3 args are printed
  * bpf_printk w/ 0 format args compiles
  * bpf_trace_vprintk call w/ a fmt specifier but NULL fmt data fails

Approach and code are borrowed from trace_printk test.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-9-davemarchevsky@fb.com

1 files changed, 33 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/trace_vprintk.c b/tools/testing/selftests/bpf/progs/trace_vprintk.c
new file mode 100644
index 000000000000..d327241ba047
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/trace_vprintk.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int null_data_vprintk_ret = 0;
+int trace_vprintk_ret = 0;
+int trace_vprintk_ran = 0;
+
+SEC("fentry/__x64_sys_nanosleep")
+int sys_enter(void *ctx)
+{
+	static const char one[] = "1";
+	static const char three[] = "3";
+	static const char five[] = "5";
+	static const char seven[] = "7";
+	static const char nine[] = "9";
+	static const char f[] = "%pS\n";
+
+	/* runner doesn't search for \t, just ensure it compiles */
+	bpf_printk("\t");
+
+	trace_vprintk_ret = __bpf_vprintk("%s,%d,%s,%d,%s,%d,%s,%d,%s,%d %d\n",
+		one, 2, three, 4, five, 6, seven, 8, nine, 10, ++trace_vprintk_ran);
+
+	/* non-NULL fmt w/ NULL data should result in error */
+	null_data_vprintk_ret = bpf_trace_vprintk(f, sizeof(f), NULL, 0);
+	return 0;
+}