selftests/bpf: Fix RELEASE build failure with gcc14

With gcc14, when building with RELEASE=1, I hit four below compilation
failure:

Error 1:
In file included from test_loader.c:6:
test_loader.c: In function ‘run_subtest’: test_progs.h:194:17:
error: ‘retval’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]
194 | fprintf(stdout, ##format); \
| ^~~~~~~
test_loader.c:958:13: note: ‘retval’ was declared here
958 | int retval, err, i;
| ^~~~~~

The uninitialized var 'retval' actually could cause incorrect result.

Error 2:
In function ‘test_fd_array_cnt’:
prog_tests/fd_array.c:71:14: error: ‘btf_id’ may be used uninitialized in this
function [-Werror=maybe-uninitialized]
71 | fd = bpf_btf_get_fd_by_id(id);
| ^~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/fd_array.c:302:15: note: ‘btf_id’ was declared here
302 | __u32 btf_id;
| ^~~~~~

Changing ASSERT_GE to ASSERT_EQ can fix the compilation error. Otherwise,
there is no functionality change.

Error 3:
prog_tests/tailcalls.c: In function ‘test_tailcall_hierarchy_count’:
prog_tests/tailcalls.c:1402:23: error: ‘fentry_data_fd’ may be used uninitialized
in this function [-Werror=maybe-uninitialized]
1402 | err = bpf_map_lookup_elem(fentry_data_fd, &i, &val);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The code is correct. The change intends to silence gcc errors.

Error 4: (this error only happens on arm64)
In file included from prog_tests/log_buf.c:4:
prog_tests/log_buf.c: In function ‘bpf_prog_load_log_buf’:
./test_progs.h:390:22: error: ‘log_buf’ may be used uninitialized [-Werror=maybe-uninitialized]
390 | int ___err = libbpf_get_error(___res); \
| ^~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/log_buf.c:158:14: note: in expansion of macro ‘ASSERT_OK_PTR’
158 | if (!ASSERT_OK_PTR(log_buf, "log_buf_alloc"))
| ^~~~~~~~~~~~~
In file included from selftests/bpf/tools/include/bpf/bpf.h:32,
from ./test_progs.h:36:
selftests/bpf/tools/include/bpf/libbpf_legacy.h:113:17:
note: by argument 1 of type ‘const void *’ to ‘libbpf_get_error’ declared here
113 | LIBBPF_API long libbpf_get_error(const void *ptr);
| ^~~~~~~~~~~~~~~~

Adding a pragma to disable maybe-uninitialized fixed the issue.

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

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

···
 
 	/* btf should still exist when original file descriptor is closed */
 	err = get_btf_id_by_fd(extra_fds[0], &btf_id);
-	if (!ASSERT_GE(err, 0, "get_btf_id_by_fd"))
+	if (!ASSERT_EQ(err, 0, "get_btf_id_by_fd"))
 		goto cleanup;
 
 	Close(extra_fds[0]);

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

···
 #include "test_log_buf.skel.h"
 #include "bpf_util.h"
 
+#if !defined(__clang__)
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
 static size_t libbpf_log_pos;
 static char libbpf_log_buf[1024 * 1024];
 static bool libbpf_log_error;

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

···
 					  bool test_fexit,
 					  bool test_fentry_entry)
 {
-	int err, map_fd, prog_fd, main_data_fd, fentry_data_fd, fexit_data_fd, i, val;
+	int err, map_fd, prog_fd, main_data_fd, fentry_data_fd = 0, fexit_data_fd = 0, i, val;
 	struct bpf_object *obj = NULL, *fentry_obj = NULL, *fexit_obj = NULL;
 	struct bpf_link *fentry_link = NULL, *fexit_link = NULL;
 	struct bpf_program *prog, *fentry_prog;

tools/testing/selftests/bpf/test_loader.c

···
 			}
 		}
 
-		do_prog_test_run(bpf_program__fd(tprog), &retval,
-				 bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false);
-		if (retval != subspec->retval && subspec->retval != POINTER_VALUE) {
+		err = do_prog_test_run(bpf_program__fd(tprog), &retval,
+				       bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false);
+		if (!err && retval != subspec->retval && subspec->retval != POINTER_VALUE) {
 			PRINT_FAIL("Unexpected retval: %d != %d\n", retval, subspec->retval);
 			goto tobj_cleanup;
 		}