selftests/bpf: Add CO-RE relocs selftest relying on kernel module BTF

Add a self-tests validating libbpf is able to perform CO-RE relocations
against the type defined in kernel module BTF. if bpf_testmod.o is not
supported by the kernel (e.g., due to version mismatch), skip tests, instead
of failing.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-9-andrii@kernel.org

1 files changed, 66 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_module.c b/tools/testing/selftests/bpf/progs/test_core_reloc_module.c
new file mode 100644
index 000000000000..d1840c1a9d36
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_module.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct bpf_testmod_test_read_ctx {
+	/* field order is mixed up */
+	size_t len;
+	char *buf;
+	loff_t off;
+} __attribute__((preserve_access_index));
+
+struct {
+	char in[256];
+	char out[256];
+	bool skip;
+	uint64_t my_pid_tgid;
+} data = {};
+
+struct core_reloc_module_output {
+	long long len;
+	long long off;
+	int read_ctx_sz;
+	bool read_ctx_exists;
+	bool buf_exists;
+	bool len_exists;
+	bool off_exists;
+	/* we have test_progs[-flavor], so cut flavor part */
+	char comm[sizeof("test_progs")];
+	int comm_len;
+};
+
+SEC("raw_tp/bpf_testmod_test_read")
+int BPF_PROG(test_core_module,
+	     struct task_struct *task,
+	     struct bpf_testmod_test_read_ctx *read_ctx)
+{
+	struct core_reloc_module_output *out = (void *)&data.out;
+	__u64 pid_tgid = bpf_get_current_pid_tgid();
+	__u32 real_tgid = (__u32)(pid_tgid >> 32);
+	__u32 real_pid = (__u32)pid_tgid;
+
+	if (data.my_pid_tgid != pid_tgid)
+		return 0;
+
+	if (BPF_CORE_READ(task, pid) != real_pid || BPF_CORE_READ(task, tgid) != real_tgid)
+		return 0;
+
+	out->len = BPF_CORE_READ(read_ctx, len);
+	out->off = BPF_CORE_READ(read_ctx, off);
+
+	out->read_ctx_sz = bpf_core_type_size(struct bpf_testmod_test_read_ctx);
+	out->read_ctx_exists = bpf_core_type_exists(struct bpf_testmod_test_read_ctx);
+	out->buf_exists = bpf_core_field_exists(read_ctx->buf);
+	out->off_exists = bpf_core_field_exists(read_ctx->off);
+	out->len_exists = bpf_core_field_exists(read_ctx->len);
+
+	out->comm_len = BPF_CORE_READ_STR_INTO(&out->comm, task, comm);
+
+	return 0;
+}