selftests/bpf: add CO-RE relocs misc tests

Add tests validating few edge-cases of capturing offset relocations.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -0,0 +1,5 @@
+#include "core_reloc_types.h"
+
+void f1(struct core_reloc_misc___a x) {}
+void f2(struct core_reloc_misc___b x) {}
+void f3(struct core_reloc_misc_extensible x) {}

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

@@ -640,3 +640,28 @@ struct core_reloc_ints___err_wrong_sz_64 {
 	uint32_t	u64_field; /* not 64-bit anymore */
 	int32_t		s64_field; /* not 64-bit anymore */
 };
+
+/*
+ * MISC
+ */
+struct core_reloc_misc_output {
+	int a, b, c;
+};
+
+struct core_reloc_misc___a {
+	int a1;
+	int a2;
+};
+
+struct core_reloc_misc___b {
+	int b1;
+	int b2;
+};
+
+/* this one extends core_reloc_misc_extensible struct from BPF prog */
+struct core_reloc_misc_extensible {
+	int a;
+	int b;
+	int c;
+	int d;
+};

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

@@ -0,0 +1,57 @@
+// 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_misc_output {
+	int a, b, c;
+};
+
+struct core_reloc_misc___a {
+	int a1;
+	int a2;
+};
+
+struct core_reloc_misc___b {
+	int b1;
+	int b2;
+};
+
+/* fixed two first members, can be extended with new fields */
+struct core_reloc_misc_extensible {
+	int a;
+	int b;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_misc(void *ctx)
+{
+	struct core_reloc_misc___a *in_a = (void *)&data.in;
+	struct core_reloc_misc___b *in_b = (void *)&data.in;
+	struct core_reloc_misc_extensible *in_ext = (void *)&data.in;
+	struct core_reloc_misc_output *out = (void *)&data.out;
+
+	/* record two different relocations with the same accessor string */
+	if (BPF_CORE_READ(&out->a, &in_a->a1) ||	/* accessor: 0:0 */
+	    BPF_CORE_READ(&out->b, &in_b->b1))		/* accessor: 0:0 */
+		return 1;
+
+	/* Validate relocations capture array-only accesses for structs with
+	 * fixed header, but with potentially extendable tail. This will read
+	 * first 4 bytes of 2nd element of in_ext array of potentially
+	 * variably sized struct core_reloc_misc_extensible. */ 
+	if (BPF_CORE_READ(&out->c, &in_ext[2]))		/* accessor: 2 */
+		return 1;
+
+	return 0;
+}
+