selftests/bpf: Add unit tests for global functions

test_global_func[12] - check 512 stack limit.
test_global_func[34] - check 8 frame call chain limit.
test_global_func5    - check that non-ctx pointer cannot be passed into
                       a function that expects context.
test_global_func6    - check that ctx pointer is unmodified.
test_global_func7    - check that global function returns scalar.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200110064124.1760511-7-ast@kernel.org

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <test_progs.h>
+
+const char *err_str;
+bool found;
+
+static int libbpf_debug_print(enum libbpf_print_level level,
+			      const char *format, va_list args)
+{
+	char *log_buf;
+
+	if (level != LIBBPF_WARN ||
+	    strcmp(format, "libbpf: \n%s\n")) {
+		vprintf(format, args);
+		return 0;
+	}
+
+	log_buf = va_arg(args, char *);
+	if (!log_buf)
+		goto out;
+	if (strstr(log_buf, err_str) == 0)
+		found = true;
+out:
+	printf(format, log_buf);
+	return 0;
+}
+
+extern int extra_prog_load_log_flags;
+
+static int check_load(const char *file)
+{
+	struct bpf_prog_load_attr attr;
+	struct bpf_object *obj = NULL;
+	int err, prog_fd;
+
+	memset(&attr, 0, sizeof(struct bpf_prog_load_attr));
+	attr.file = file;
+	attr.prog_type = BPF_PROG_TYPE_UNSPEC;
+	attr.log_level = extra_prog_load_log_flags;
+	attr.prog_flags = BPF_F_TEST_RND_HI32;
+	found = false;
+	err = bpf_prog_load_xattr(&attr, &obj, &prog_fd);
+	bpf_object__close(obj);
+	return err;
+}
+
+struct test_def {
+	const char *file;
+	const char *err_str;
+};
+
+void test_test_global_funcs(void)
+{
+	struct test_def tests[] = {
+		{ "test_global_func1.o", "combined stack size of 4 calls is 544" },
+		{ "test_global_func2.o" },
+		{ "test_global_func3.o" , "the call stack of 8 frames" },
+		{ "test_global_func4.o" },
+		{ "test_global_func5.o" , "expected pointer to ctx, but got PTR" },
+		{ "test_global_func6.o" , "modified ctx ptr R2" },
+		{ "test_global_func7.o" , "foo() doesn't return scalar" },
+	};
+	libbpf_print_fn_t old_print_fn = NULL;
+	int err, i, duration = 0;
+
+	old_print_fn = libbpf_set_print(libbpf_debug_print);
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		const struct test_def *test = &tests[i];
+
+		if (!test__start_subtest(test->file))
+			continue;
+
+		err_str = test->err_str;
+		err = check_load(test->file);
+		CHECK_FAIL(!!err ^ !!err_str);
+		if (err_str)
+			CHECK(found, "", "expected string '%s'", err_str);
+	}
+	libbpf_set_print(old_print_fn);
+}

tools/testing/selftests/bpf/progs/test_global_func1.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <stddef.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+#ifndef MAX_STACK
+#define MAX_STACK (512 - 3 * 32 + 8)
+#endif
+
+static __attribute__ ((noinline))
+int f0(int var, struct __sk_buff *skb)
+{
+	return skb->len;
+}
+
+__attribute__ ((noinline))
+int f1(struct __sk_buff *skb)
+{
+	volatile char buf[MAX_STACK] = {};
+
+	return f0(0, skb) + skb->len;
+}
+
+int f3(int, struct __sk_buff *skb, int);
+
+__attribute__ ((noinline))
+int f2(int val, struct __sk_buff *skb)
+{
+	return f1(skb) + f3(val, skb, 1);
+}
+
+__attribute__ ((noinline))
+int f3(int val, struct __sk_buff *skb, int var)
+{
+	volatile char buf[MAX_STACK] = {};
+
+	return skb->ifindex * val * var;
+}
+
+SEC("classifier/test")
+int test_cls(struct __sk_buff *skb)
+{
+	return f0(1, skb) + f1(skb) + f2(2, skb) + f3(3, skb, 4);
+}

tools/testing/selftests/bpf/progs/test_global_func2.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#define MAX_STACK (512 - 3 * 32)
+#include "test_global_func1.c"

tools/testing/selftests/bpf/progs/test_global_func3.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <stddef.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+__attribute__ ((noinline))
+int f1(struct __sk_buff *skb)
+{
+	return skb->len;
+}
+
+__attribute__ ((noinline))
+int f2(int val, struct __sk_buff *skb)
+{
+	return f1(skb) + val;
+}
+
+__attribute__ ((noinline))
+int f3(int val, struct __sk_buff *skb, int var)
+{
+	return f2(var, skb) + val;
+}
+
+__attribute__ ((noinline))
+int f4(struct __sk_buff *skb)
+{
+	return f3(1, skb, 2);
+}
+
+__attribute__ ((noinline))
+int f5(struct __sk_buff *skb)
+{
+	return f4(skb);
+}
+
+__attribute__ ((noinline))
+int f6(struct __sk_buff *skb)
+{
+	return f5(skb);
+}
+
+__attribute__ ((noinline))
+int f7(struct __sk_buff *skb)
+{
+	return f6(skb);
+}
+
+#ifndef NO_FN8
+__attribute__ ((noinline))
+int f8(struct __sk_buff *skb)
+{
+	return f7(skb);
+}
+#endif
+
+SEC("classifier/test")
+int test_cls(struct __sk_buff *skb)
+{
+#ifndef NO_FN8
+	return f8(skb);
+#else
+	return f7(skb);
+#endif
+}

tools/testing/selftests/bpf/progs/test_global_func4.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#define NO_FN8
+#include "test_global_func3.c"

tools/testing/selftests/bpf/progs/test_global_func5.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <stddef.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+__attribute__ ((noinline))
+int f1(struct __sk_buff *skb)
+{
+	return skb->len;
+}
+
+int f3(int, struct __sk_buff *skb);
+
+__attribute__ ((noinline))
+int f2(int val, struct __sk_buff *skb)
+{
+	return f1(skb) + f3(val, (void *)&val); /* type mismatch */
+}
+
+__attribute__ ((noinline))
+int f3(int val, struct __sk_buff *skb)
+{
+	return skb->ifindex * val;
+}
+
+SEC("classifier/test")
+int test_cls(struct __sk_buff *skb)
+{
+	return f1(skb) + f2(2, skb) + f3(3, skb);
+}

tools/testing/selftests/bpf/progs/test_global_func6.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <stddef.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+__attribute__ ((noinline))
+int f1(struct __sk_buff *skb)
+{
+	return skb->len;
+}
+
+int f3(int, struct __sk_buff *skb);
+
+__attribute__ ((noinline))
+int f2(int val, struct __sk_buff *skb)
+{
+	return f1(skb) + f3(val, skb + 1); /* type mismatch */
+}
+
+__attribute__ ((noinline))
+int f3(int val, struct __sk_buff *skb)
+{
+	return skb->ifindex * val;
+}
+
+SEC("classifier/test")
+int test_cls(struct __sk_buff *skb)
+{
+	return f1(skb) + f2(2, skb) + f3(3, skb);
+}

tools/testing/selftests/bpf/progs/test_global_func7.c

+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2020 Facebook */
+#include <stddef.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+__attribute__ ((noinline))
+void foo(struct __sk_buff *skb)
+{
+	skb->tc_index = 0;
+}
+
+SEC("classifier/test")
+int test_cls(struct __sk_buff *skb)
+{
+	foo(skb);
+	return 0;
+}