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linux-7.2.3/tools/testing/selftests/bpf/progs/raw_tp_null.c

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int tid;
+int i;
+
+SEC("tp_btf/bpf_testmod_test_raw_tp_null_tp")
+int BPF_PROG(test_raw_tp_null, struct sk_buff *skb)
+{
+	struct task_struct *task = bpf_get_current_task_btf();
+
+	if (task->pid != tid)
+		return 0;
+
+	/* If dead code elimination kicks in, the increment +=2 will be
+	 * removed. For raw_tp programs attaching to tracepoints in kernel
+	 * modules, we mark input arguments as PTR_MAYBE_NULL, so branch
+	 * prediction should never kick in.
+	 */
+	asm volatile ("%[i] += 1; if %[ctx] != 0 goto +1; %[i] += 2;"
+			: [i]"+r"(i)
+			: [ctx]"r"(skb)
+			: "memory");
+	return 0;
+}