samples/bpf, selftests/bpf: Use bpf_probe_read_kernel

A handful of samples and selftests fail to build on s390, because
after commit 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}()
only to archs where they work") bpf_probe_read is not available
anymore.

Fix by using bpf_probe_read_kernel.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200720114806.88823-1-iii@linux.ibm.com
diff --git a/samples/bpf/tracex1_kern.c b/samples/bpf/tracex1_kern.c
index 8e2610e..3f4599c 100644
--- a/samples/bpf/tracex1_kern.c
+++ b/samples/bpf/tracex1_kern.c
@@ -11,7 +11,12 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
-#define _(P) ({typeof(P) val = 0; bpf_probe_read(&val, sizeof(val), &P); val;})
+#define _(P)                                                                   \
+	({                                                                     \
+		typeof(P) val = 0;                                             \
+		bpf_probe_read_kernel(&val, sizeof(val), &(P));                \
+		val;                                                           \
+	})
 
 /* kprobe is NOT a stable ABI
  * kernel functions can be removed, renamed or completely change semantics.
@@ -34,7 +39,7 @@ int bpf_prog1(struct pt_regs *ctx)
 	dev = _(skb->dev);
 	len = _(skb->len);
 
-	bpf_probe_read(devname, sizeof(devname), dev->name);
+	bpf_probe_read_kernel(devname, sizeof(devname), dev->name);
 
 	if (devname[0] == 'l' && devname[1] == 'o') {
 		char fmt[] = "skb %p len %d\n";