selftests/bpf: Add basic USDT selftests

Add semaphore-based USDT to test_progs itself and write basic tests to
valicate both auto-attachment and manual attachment logic, as well as
BPF-side functionality.

Also add subtests to validate that libbpf properly deduplicates USDT
specs and handles spec overflow situations correctly, as well as proper
"rollback" of partially-attached multi-spec USDT.

BPF-side of selftest intentionally consists of two files to validate
that usdt.bpf.h header can be included from multiple source code files
that are subsequently linked into final BPF object file without causing
any symbol duplication or other issues. We are validating that __weak
maps and bpf_usdt_xxx() API functions defined in usdt.bpf.h do work as
intended.

USDT selftests utilize sys/sdt.h header that on Ubuntu systems comes
from systemtap-sdt-devel package. But to simplify everyone's life,
including CI but especially casual contributors to bpf/bpf-next that
are trying to build selftests, I've checked in sys/sdt.h header from [0]
directly. This way it will work on all architectures and distros without
having to figure it out for every relevant combination and adding any
extra implicit package dependencies.

  [0] https://sourceware.org/git?p=systemtap.git;a=blob_plain;f=includes/sys/sdt.h;h=ca0162b4dc57520b96638c8ae79ad547eb1dd3a1;hb=HEAD

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20220404234202.331384-7-andrii@kernel.org

1 files changed, 96 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
new file mode 100644
index 000000000000..505aab9a5234
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_usdt.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/usdt.bpf.h>
+
+int my_pid;
+
+int usdt0_called;
+u64 usdt0_cookie;
+int usdt0_arg_cnt;
+int usdt0_arg_ret;
+
+SEC("usdt")
+int usdt0(struct pt_regs *ctx)
+{
+	long tmp;
+
+	if (my_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&usdt0_called, 1);
+
+	usdt0_cookie = bpf_usdt_cookie(ctx);
+	usdt0_arg_cnt = bpf_usdt_arg_cnt(ctx);
+	/* should return -ENOENT for any arg_num */
+	usdt0_arg_ret = bpf_usdt_arg(ctx, bpf_get_prandom_u32(), &tmp);
+	return 0;
+}
+
+int usdt3_called;
+u64 usdt3_cookie;
+int usdt3_arg_cnt;
+int usdt3_arg_rets[3];
+u64 usdt3_args[3];
+
+SEC("usdt//proc/self/exe:test:usdt3")
+int usdt3(struct pt_regs *ctx)
+{
+	long tmp;
+
+	if (my_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&usdt3_called, 1);
+
+	usdt3_cookie = bpf_usdt_cookie(ctx);
+	usdt3_arg_cnt = bpf_usdt_arg_cnt(ctx);
+
+	usdt3_arg_rets[0] = bpf_usdt_arg(ctx, 0, &tmp);
+	usdt3_args[0] = (int)tmp;
+
+	usdt3_arg_rets[1] = bpf_usdt_arg(ctx, 1, &tmp);
+	usdt3_args[1] = (long)tmp;
+
+	usdt3_arg_rets[2] = bpf_usdt_arg(ctx, 2, &tmp);
+	usdt3_args[2] = (uintptr_t)tmp;
+
+	return 0;
+}
+
+int usdt12_called;
+u64 usdt12_cookie;
+int usdt12_arg_cnt;
+u64 usdt12_args[12];
+
+SEC("usdt//proc/self/exe:test:usdt12")
+int BPF_USDT(usdt12, int a1, int a2, long a3, long a4, unsigned a5,
+		     long a6, __u64 a7, uintptr_t a8, int a9, short a10,
+		     short a11, signed char a12)
+{
+	if (my_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&usdt12_called, 1);
+
+	usdt12_cookie = bpf_usdt_cookie(ctx);
+	usdt12_arg_cnt = bpf_usdt_arg_cnt(ctx);
+
+	usdt12_args[0] = a1;
+	usdt12_args[1] = a2;
+	usdt12_args[2] = a3;
+	usdt12_args[3] = a4;
+	usdt12_args[4] = a5;
+	usdt12_args[5] = a6;
+	usdt12_args[6] = a7;
+	usdt12_args[7] = a8;
+	usdt12_args[8] = a9;
+	usdt12_args[9] = a10;
+	usdt12_args[10] = a11;
+	usdt12_args[11] = a12;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";