[PATCH v6 06/12] samples/bpf/test_overhead_kprobe_kern: make it adopt to task comm size change

[Yafang Shao <laoar.shao@gmail.com>]

bpf_probe_read_kernel_str() will add a nul terminator to the dst, then
we don't care about if the dst size is big enough. This patch also
replaces the hard-coded 16 with TASK_COMM_LEN to make it adopt to task
comm size change.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
---
 samples/bpf/test_overhead_kprobe_kern.c | 11 ++++++-----
 samples/bpf/test_overhead_tp_kern.c     |  5 +++--
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/samples/bpf/test_overhead_kprobe_kern.c b/samples/bpf/test_overhead_kprobe_kern.c
index f6d593e47037..8fdd2c9c56b2 100644
--- a/samples/bpf/test_overhead_kprobe_kern.c
+++ b/samples/bpf/test_overhead_kprobe_kern.c
@@ -6,6 +6,7 @@
  */
 #include <linux/version.h>
 #include <linux/ptrace.h>
+#include <linux/sched.h>
 #include <uapi/linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
@@ -22,17 +23,17 @@ int prog(struct pt_regs *ctx)
 {
 	struct signal_struct *signal;
 	struct task_struct *tsk;
-	char oldcomm[16] = {};
-	char newcomm[16] = {};
+	char oldcomm[TASK_COMM_LEN] = {};
+	char newcomm[TASK_COMM_LEN] = {};
 	u16 oom_score_adj;
 	u32 pid;
 
 	tsk = (void *)PT_REGS_PARM1(ctx);
 
 	pid = _(tsk->pid);
-	bpf_probe_read_kernel(oldcomm, sizeof(oldcomm), &tsk->comm);
-	bpf_probe_read_kernel(newcomm, sizeof(newcomm),
-			      (void *)PT_REGS_PARM2(ctx));
+	bpf_probe_read_kernel_str(oldcomm, sizeof(oldcomm), &tsk->comm);
+	bpf_probe_read_kernel_str(newcomm, sizeof(newcomm),
+				  (void *)PT_REGS_PARM2(ctx));
 	signal = _(tsk->signal);
 	oom_score_adj = _(signal->oom_score_adj);
 	return 0;
diff --git a/samples/bpf/test_overhead_tp_kern.c b/samples/bpf/test_overhead_tp_kern.c
index eaa32693f8fc..80edadacb692 100644
--- a/samples/bpf/test_overhead_tp_kern.c
+++ b/samples/bpf/test_overhead_tp_kern.c
@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#include <linux/sched.h>
 #include <uapi/linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 
@@ -11,8 +12,8 @@
 struct task_rename {
 	__u64 pad;
 	__u32 pid;
-	char oldcomm[16];
-	char newcomm[16];
+	char oldcomm[TASK_COMM_LEN];
+	char newcomm[TASK_COMM_LEN];
 	__u16 oom_score_adj;
 };
 SEC("tracepoint/task/task_rename")
-- 
2.17.1