selftests/bpf: Test for btf_load command.

Improve selftest to check that btf_load is working from bpf program.

Signed-off-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/syscall.c

···
 	int max_entries;
 	int map_fd;
 	int prog_fd;
+	int btf_fd;
 };
 
 void test_syscall(void)
···
 		close(ctx.prog_fd);
 	if (ctx.map_fd > 0)
 		close(ctx.map_fd);
+	if (ctx.btf_fd > 0)
+		close(ctx.btf_fd);
 }

tools/testing/selftests/bpf/progs/syscall.c

···
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include <../../../tools/include/linux/filter.h>
+#include <linux/btf.h>
 
 char _license[] SEC("license") = "GPL";
 
···
 	int max_entries;
 	int map_fd;
 	int prog_fd;
+	int btf_fd;
 };
+
+#define BTF_INFO_ENC(kind, kind_flag, vlen) \
+	((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
+#define BTF_TYPE_ENC(name, info, size_or_type) (name), (info), (size_or_type)
+#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
+	((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
+#define BTF_TYPE_INT_ENC(name, encoding, bits_offset, bits, sz) \
+	BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_INT, 0, 0), sz), \
+	BTF_INT_ENC(encoding, bits_offset, bits)
+
+static int btf_load(void)
+{
+	struct btf_blob {
+		struct btf_header btf_hdr;
+		__u32 types[8];
+		__u32 str;
+	} raw_btf = {
+		.btf_hdr = {
+			.magic = BTF_MAGIC,
+			.version = BTF_VERSION,
+			.hdr_len = sizeof(struct btf_header),
+			.type_len = sizeof(__u32) * 8,
+			.str_off = sizeof(__u32) * 8,
+			.str_len = sizeof(__u32),
+		},
+		.types = {
+			/* long */
+			BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 64, 8),  /* [1] */
+			/* unsigned long */
+			BTF_TYPE_INT_ENC(0, 0, 0, 64, 8),  /* [2] */
+		},
+	};
+	static union bpf_attr btf_load_attr = {
+		.btf_size = sizeof(raw_btf),
+	};
+
+	btf_load_attr.btf = (long)&raw_btf;
+	return bpf_sys_bpf(BPF_BTF_LOAD, &btf_load_attr, sizeof(btf_load_attr));
+}
 
 SEC("syscall")
 int bpf_prog(struct args *ctx)
···
 		.map_type = BPF_MAP_TYPE_HASH,
 		.key_size = 8,
 		.value_size = 8,
+		.btf_key_type_id = 1,
+		.btf_value_type_id = 2,
 	};
 	static union bpf_attr map_update_attr = { .map_fd = 1, };
 	static __u64 key = 12;
···
 	};
 	int ret;
 
+	ret = btf_load();
+	if (ret <= 0)
+		return ret;
+
+	ctx->btf_fd = ret;
 	map_create_attr.max_entries = ctx->max_entries;
+	map_create_attr.btf_fd = ret;
+
 	prog_load_attr.license = (long) license;
 	prog_load_attr.insns = (long) insns;
 	prog_load_attr.log_buf = ctx->log_buf;