selftests/bpf: Fix sk_assign on s390x

sk_assign is failing on an s390x machine running Debian "bookworm" for
2 reasons: legacy server_map definition and uninitialized addrlen in
recvfrom() call.

Fix by adding a new-style server_map definition and dropping addrlen
(recvfrom() allows NULL values for src_addr and addrlen).

Since the test should support tc built without libbpf, build the prog
twice: with the old-style definition and with the new-style definition,
then select the right one at runtime. This could be done at compile
time too, but this would not be cross-compilation friendly.

Signed-off-by: Ilya Leoshkevich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 static bool
 configure_stack(void)
 {
+	char tc_version[128];
 	char tc_cmd[BUFSIZ];
+	char *prog;
+	FILE *tc;
+
+	/* Check whether tc is built with libbpf. */
+	tc = popen("tc -V", "r");
+	if (CHECK_FAIL(!tc))
+		return false;
+	if (CHECK_FAIL(!fgets(tc_version, sizeof(tc_version), tc)))
+		return false;
+	if (strstr(tc_version, ", libbpf "))
+		prog = "test_sk_assign_libbpf.bpf.o";
+	else
+		prog = "test_sk_assign.bpf.o";
+	if (CHECK_FAIL(pclose(tc)))
+		return false;
 
 	/* Move to a new networking namespace */
 	if (CHECK_FAIL(unshare(CLONE_NEWNET)))
···
 	/* Load qdisc, BPF program */
 	if (CHECK_FAIL(system("tc qdisc add dev lo clsact")))
 		return false;
-	sprintf(tc_cmd, "%s %s %s %s", "tc filter add dev lo ingress bpf",
-		       "direct-action object-file ./test_sk_assign.bpf.o",
+	sprintf(tc_cmd, "%s %s %s %s %s", "tc filter add dev lo ingress bpf",
+		       "direct-action object-file", prog,
 		       "section tc",
 		       (env.verbosity < VERBOSE_VERY) ? " 2>/dev/null" : "verbose");
 	if (CHECK(system(tc_cmd), "BPF load failed;",
···
 static ssize_t
 rcv_msg(int srv_client, int type)
 {
-	struct sockaddr_storage ss;
 	char buf[BUFSIZ];
-	socklen_t slen;
 
 	if (type == SOCK_STREAM)
 		return read(srv_client, &buf, sizeof(buf));
 	else
-		return recvfrom(srv_client, &buf, sizeof(buf), 0,
-				(struct sockaddr *)&ss, &slen);
+		return recvfrom(srv_client, &buf, sizeof(buf), 0, NULL, NULL);
 }
 
 static int

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

···
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
+#if defined(IPROUTE2_HAVE_LIBBPF)
+/* Use a new-style map definition. */
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__type(key, int);
+	__type(value, __u64);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+	__uint(max_entries, 1);
+} server_map SEC(".maps");
+#else
 /* Pin map under /sys/fs/bpf/tc/globals/<map name> */
 #define PIN_GLOBAL_NS 2
 
···
 	.max_elem = 1,
 	.pinning = PIN_GLOBAL_NS,
 };
+#endif
 
 char _license[] SEC("license") = "GPL";
 

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

···
+// SPDX-License-Identifier: GPL-2.0
+#define IPROUTE2_HAVE_LIBBPF
+#include "test_sk_assign.c"