selftests/bpf: add CO-RE relocs struct flavors tests

Add tests verifying that BPF program can use various struct/union
"flavors" to extract data from the same target struct/union.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

 // SPDX-License-Identifier: GPL-2.0
 #include <test_progs.h>
+#include "progs/core_reloc_types.h"
+
+#define STRUCT_TO_CHAR_PTR(struct_name) (const char *)&(struct struct_name)
+
+#define FLAVORS_DATA(struct_name) STRUCT_TO_CHAR_PTR(struct_name) {	\
+	.a = 42,							\
+	.b = 0xc001,							\
+	.c = 0xbeef,							\
+}
+
+#define FLAVORS_CASE_COMMON(name)					\
+	.case_name = #name,						\
+	.bpf_obj_file = "test_core_reloc_flavors.o",			\
+	.btf_src_file = "btf__core_reloc_" #name ".o"			\
+
+#define FLAVORS_CASE(name) {						\
+	FLAVORS_CASE_COMMON(name),					\
+	.input = FLAVORS_DATA(core_reloc_##name),			\
+	.input_len = sizeof(struct core_reloc_##name),			\
+	.output = FLAVORS_DATA(core_reloc_flavors),			\
+	.output_len = sizeof(struct core_reloc_flavors),		\
+}
+
+#define FLAVORS_ERR_CASE(name) {					\
+	FLAVORS_CASE_COMMON(name),					\
+	.fails = true,							\
+}
 
 struct core_reloc_test_case {
 	const char *case_name;
@@ -23,6 +50,13 @@ static struct core_reloc_test_case test_cases[] = {
 		.output = "\1", /* true */
 		.output_len = 1,
 	},
+
+	/* validate BPF program can use multiple flavors to match against
+	 * single target BTF type
+	 */
+	FLAVORS_CASE(flavors),
+
+	FLAVORS_ERR_CASE(flavors__err_wrong_name),
 };
 
 struct data {

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

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_flavors x) {}

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

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_flavors__err_wrong_name x) {}

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

+/*
+ * FLAVORS
+ */
+struct core_reloc_flavors {
+	int a;
+	int b;
+	int c;
+};
+
+/* this is not a flavor, as it doesn't have triple underscore */
+struct core_reloc_flavors__err_wrong_name {
+	int a;
+	int b;
+	int c;
+};

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

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <linux/bpf.h>
+#include <stdint.h>
+#include "bpf_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+static volatile struct data {
+	char in[256];
+	char out[256];
+} data;
+
+struct core_reloc_flavors {
+	int a;
+	int b;
+	int c;
+};
+
+/* local flavor with reversed layout */
+struct core_reloc_flavors___reversed {
+	int c;
+	int b;
+	int a;
+};
+
+/* local flavor with nested/overlapping layout */
+struct core_reloc_flavors___weird {
+	struct {
+		int b;
+	};
+	/* a and c overlap in local flavor, but this should still work
+	 * correctly with target original flavor
+	 */
+	union {
+		int a;
+		int c;
+	};
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_flavors(void *ctx)
+{
+	struct core_reloc_flavors *in_orig = (void *)&data.in;
+	struct core_reloc_flavors___reversed *in_rev = (void *)&data.in;
+	struct core_reloc_flavors___weird *in_weird = (void *)&data.in;
+	struct core_reloc_flavors *out = (void *)&data.out;
+
+	/* read a using weird layout */
+	if (BPF_CORE_READ(&out->a, &in_weird->a))
+		return 1;
+	/* read b using reversed layout */
+	if (BPF_CORE_READ(&out->b, &in_rev->b))
+		return 1;
+	/* read c using original layout */
+	if (BPF_CORE_READ(&out->c, &in_orig->c))
+		return 1;
+
+	return 0;
+}
+