selftests/bpf: Add field existence CO-RE relocs tests

Add a bunch of tests validating CO-RE is handling field existence
relocation. Relaxed CO-RE relocation mode is activated for these new
tests to prevent libbpf from rejecting BPF object for no-match
relocation, even though test BPF program is not going to use that
relocation, if field is missing.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191015182849.3922287-6-andriin@fb.com

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

@@ -174,6 +174,21 @@
 	.fails = true,							\
 }
 
+#define EXISTENCE_DATA(struct_name) STRUCT_TO_CHAR_PTR(struct_name) {	\
+	.a = 42,							\
+}
+
+#define EXISTENCE_CASE_COMMON(name)					\
+	.case_name = #name,						\
+	.bpf_obj_file = "test_core_reloc_existence.o",			\
+	.btf_src_file = "btf__core_reloc_" #name ".o",			\
+	.relaxed_core_relocs = true					\
+
+#define EXISTENCE_ERR_CASE(name) {					\
+	EXISTENCE_CASE_COMMON(name),					\
+	.fails = true,							\
+}
+
 struct core_reloc_test_case {
 	const char *case_name;
 	const char *bpf_obj_file;
@@ -183,6 +198,7 @@ struct core_reloc_test_case {
 	const char *output;
 	int output_len;
 	bool fails;
+	bool relaxed_core_relocs;
 };
 
 static struct core_reloc_test_case test_cases[] = {
@@ -283,6 +299,59 @@ static struct core_reloc_test_case test_cases[] = {
 		},
 		.output_len = sizeof(struct core_reloc_misc_output),
 	},
+
+	/* validate field existence checks */
+	{
+		EXISTENCE_CASE_COMMON(existence),
+		.input = STRUCT_TO_CHAR_PTR(core_reloc_existence) {
+			.a = 1,
+			.b = 2,
+			.c = 3,
+			.arr = { 4 },
+			.s = { .x = 5 },
+		},
+		.input_len = sizeof(struct core_reloc_existence),
+		.output = STRUCT_TO_CHAR_PTR(core_reloc_existence_output) {
+			.a_exists = 1,
+			.b_exists = 1,
+			.c_exists = 1,
+			.arr_exists = 1,
+			.s_exists = 1,
+			.a_value = 1,
+			.b_value = 2,
+			.c_value = 3,
+			.arr_value = 4,
+			.s_value = 5,
+		},
+		.output_len = sizeof(struct core_reloc_existence_output),
+	},
+	{
+		EXISTENCE_CASE_COMMON(existence___minimal),
+		.input = STRUCT_TO_CHAR_PTR(core_reloc_existence___minimal) {
+			.a = 42,
+		},
+		.input_len = sizeof(struct core_reloc_existence),
+		.output = STRUCT_TO_CHAR_PTR(core_reloc_existence_output) {
+			.a_exists = 1,
+			.b_exists = 0,
+			.c_exists = 0,
+			.arr_exists = 0,
+			.s_exists = 0,
+			.a_value = 42,
+			.b_value = 0xff000002u,
+			.c_value = 0xff000003u,
+			.arr_value = 0xff000004u,
+			.s_value = 0xff000005u,
+		},
+		.output_len = sizeof(struct core_reloc_existence_output),
+	},
+
+	EXISTENCE_ERR_CASE(existence__err_int_sz),
+	EXISTENCE_ERR_CASE(existence__err_int_type),
+	EXISTENCE_ERR_CASE(existence__err_int_kind),
+	EXISTENCE_ERR_CASE(existence__err_arr_kind),
+	EXISTENCE_ERR_CASE(existence__err_arr_value_type),
+	EXISTENCE_ERR_CASE(existence__err_struct_type),
 };
 
 struct data {
@@ -305,11 +374,14 @@ void test_core_reloc(void)
 
 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
 		test_case = &test_cases[i];
-
 		if (!test__start_subtest(test_case->case_name))
 			continue;
 
-		obj = bpf_object__open(test_case->bpf_obj_file);
+		LIBBPF_OPTS(bpf_object_open_opts, opts,
+			.relaxed_core_relocs = test_case->relaxed_core_relocs,
+		);
+
+		obj = bpf_object__open_file(test_case->bpf_obj_file, &opts);
 		if (CHECK(IS_ERR_OR_NULL(obj), "obj_open",
 			  "failed to open '%s': %ld\n",
 			  test_case->bpf_obj_file, PTR_ERR(obj)))

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_arr_kind x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_arr_value_type x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_kind x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_sz x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_type x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_struct_type x) {}

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

@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___minimal x) {}

tools/testing/selftests/bpf/progs/core_reloc_types.h

@@ -674,3 +674,59 @@ struct core_reloc_misc_extensible {
 	int c;
 	int d;
 };
+
+/*
+ * EXISTENCE
+ */
+struct core_reloc_existence_output {
+	int a_exists;
+	int a_value;
+	int b_exists;
+	int b_value;
+	int c_exists;
+	int c_value;
+	int arr_exists;
+	int arr_value;
+	int s_exists;
+	int s_value;
+};
+
+struct core_reloc_existence {
+	int a;
+	struct {
+		int b;
+	};
+	int c;
+	int arr[1];
+	struct {
+		int x;
+	} s;
+};
+
+struct core_reloc_existence___minimal {
+	int a;
+};
+
+struct core_reloc_existence___err_wrong_int_sz {
+	short a;
+};
+
+struct core_reloc_existence___err_wrong_int_type {
+	int b[1];
+};
+
+struct core_reloc_existence___err_wrong_int_kind {
+	struct{ int x; } c;
+};
+
+struct core_reloc_existence___err_wrong_arr_kind {
+	int arr;
+};
+
+struct core_reloc_existence___err_wrong_arr_value_type {
+	short arr[1];
+};
+
+struct core_reloc_existence___err_wrong_struct_type {
+	int s;
+};

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

@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <linux/bpf.h>
+#include <stdint.h>
+#include "bpf_helpers.h"
+#include "bpf_core_read.h"
+
+char _license[] SEC("license") = "GPL";
+
+static volatile struct data {
+	char in[256];
+	char out[256];
+} data;
+
+struct core_reloc_existence_output {
+	int a_exists;
+	int a_value;
+	int b_exists;
+	int b_value;
+	int c_exists;
+	int c_value;
+	int arr_exists;
+	int arr_value;
+	int s_exists;
+	int s_value;
+};
+
+struct core_reloc_existence {
+	struct {
+		int x;
+	} s;
+	int arr[1];
+	int a;
+	struct {
+		int b;
+	};
+	int c;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_existence(void *ctx)
+{
+	struct core_reloc_existence *in = (void *)&data.in;
+	struct core_reloc_existence_output *out = (void *)&data.out;
+
+	out->a_exists = bpf_core_field_exists(in->a);
+	if (bpf_core_field_exists(in->a))
+		out->a_value = BPF_CORE_READ(in, a);
+	else
+		out->a_value = 0xff000001u;
+
+	out->b_exists = bpf_core_field_exists(in->b);
+	if (bpf_core_field_exists(in->b))
+		out->b_value = BPF_CORE_READ(in, b);
+	else
+		out->b_value = 0xff000002u;
+
+	out->c_exists = bpf_core_field_exists(in->c);
+	if (bpf_core_field_exists(in->c))
+		out->c_value = BPF_CORE_READ(in, c);
+	else
+		out->c_value = 0xff000003u;
+
+	out->arr_exists = bpf_core_field_exists(in->arr);
+	if (bpf_core_field_exists(in->arr))
+		out->arr_value = BPF_CORE_READ(in, arr[0]);
+	else
+		out->arr_value = 0xff000004u;
+
+	out->s_exists = bpf_core_field_exists(in->s);
+	if (bpf_core_field_exists(in->s))
+		out->s_value = BPF_CORE_READ(in, s.x);
+	else
+		out->s_value = 0xff000005u;
+
+	return 0;
+}
+