Merge branch 'compile-once-run-everywhere'

Andrii Nakryiko says:

====================
This patch set implements central part of CO-RE (Compile Once - Run
Everywhere, see [0] and [1] for slides and video): relocating fields offsets.
Most of the details are written down as comments to corresponding parts of the
code.

Patch #1 adds a bunch of commonly useful btf_xxx helpers to simplify working
with BTF types.
Patch #2 converts existing libbpf code to these new helpers and removes some
of pre-existing ones.
Patch #3 adds loading of .BTF.ext offset relocations section and macros to
work with its contents.
Patch #4 implements CO-RE relocations algorithm in libbpf.
Patch #5 introduced BPF_CORE_READ macro, hiding usage of Clang's
__builtin_preserve_access_index intrinsic that records offset relocation.
Patches #6-#14 adds selftests validating various parts of relocation handling,
type compatibility, etc.

For all tests to work, you'll need latest Clang/LLVM supporting
__builtin_preserve_access_index intrinsic, used for recording offset
relocations. Kernel on which selftests run should have BTF information built
in (CONFIG_DEBUG_INFO_BTF=y).

  [0] http://vger.kernel.org/bpfconf2019.html#session-2
  [1] http://vger.kernel.org/lpc-bpf2018.html#session-2

v5->v6:
- fix bad comment formatting for real (Alexei);

v4->v5:
- drop constness for btf_xxx() helpers, allowing to avoid type casts (Alexei);
- rebase on latest bpf-next, change test__printf back to printf;

v3->v4:
- added btf_xxx helpers (Alexei);
- switched libbpf code to new helpers;
- reduced amount of logging and simplified format in few places (Alexei);
- made flavor name parsing logic more strict (exactly three underscores);
- no uname() error checking (Alexei);
- updated misc tests to reflect latest Clang fixes (Yonghong);

v2->v3:
- enclose BPF_CORE_READ args in parens (Song);

v1->v2:
- add offsetofend(), fix btf_ext optional fields checks (Song);
- add bpf_core_dump_spec() for logging spec representation;
- move special first element processing out of the loop (Song);
- typo fixes (Song);
- drop BPF_ST | BPF_MEM insn relocation (Alexei);
- extracted BPF_CORE_READ into bpf_helpers (Alexei);
- added extra tests validating Clang capturing relocs correctly (Yonghong);
- switch core_relocs.c to use sub-tests;
- updated mods tests after Clang bug was fixed (Yonghong);
- fix bug enumerating candidate types;
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/btf.h

@@ -5,6 +5,7 @@
 #define __LIBBPF_BTF_H
 
 #include <stdarg.h>
+#include <linux/btf.h>
 #include <linux/types.h>
 
 #ifdef __cplusplus
@@ -57,6 +58,10 @@ struct btf_ext_header {
 	__u32	func_info_len;
 	__u32	line_info_off;
 	__u32	line_info_len;
+
+	/* optional part of .BTF.ext header */
+	__u32	offset_reloc_off;
+	__u32	offset_reloc_len;
 };
 
 LIBBPF_API void btf__free(struct btf *btf);
@@ -120,6 +125,183 @@ LIBBPF_API void btf_dump__free(struct btf_dump *d);
 
 LIBBPF_API int btf_dump__dump_type(struct btf_dump *d, __u32 id);
 
+/*
+ * A set of helpers for easier BTF types handling
+ */
+static inline __u16 btf_kind(const struct btf_type *t)
+{
+	return BTF_INFO_KIND(t->info);
+}
+
+static inline __u16 btf_vlen(const struct btf_type *t)
+{
+	return BTF_INFO_VLEN(t->info);
+}
+
+static inline bool btf_kflag(const struct btf_type *t)
+{
+	return BTF_INFO_KFLAG(t->info);
+}
+
+static inline bool btf_is_int(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_INT;
+}
+
+static inline bool btf_is_ptr(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_PTR;
+}
+
+static inline bool btf_is_array(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_ARRAY;
+}
+
+static inline bool btf_is_struct(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_STRUCT;
+}
+
+static inline bool btf_is_union(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_UNION;
+}
+
+static inline bool btf_is_composite(const struct btf_type *t)
+{
+	__u16 kind = btf_kind(t);
+
+	return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION;
+}
+
+static inline bool btf_is_enum(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_ENUM;
+}
+
+static inline bool btf_is_fwd(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_FWD;
+}
+
+static inline bool btf_is_typedef(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_TYPEDEF;
+}
+
+static inline bool btf_is_volatile(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_VOLATILE;
+}
+
+static inline bool btf_is_const(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_CONST;
+}
+
+static inline bool btf_is_restrict(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_RESTRICT;
+}
+
+static inline bool btf_is_mod(const struct btf_type *t)
+{
+	__u16 kind = btf_kind(t);
+
+	return kind == BTF_KIND_VOLATILE ||
+	       kind == BTF_KIND_CONST ||
+	       kind == BTF_KIND_RESTRICT;
+}
+
+static inline bool btf_is_func(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_FUNC;
+}
+
+static inline bool btf_is_func_proto(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_FUNC_PROTO;
+}
+
+static inline bool btf_is_var(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_VAR;
+}
+
+static inline bool btf_is_datasec(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_DATASEC;
+}
+
+static inline __u8 btf_int_encoding(const struct btf_type *t)
+{
+	return BTF_INT_ENCODING(*(__u32 *)(t + 1));
+}
+
+static inline __u8 btf_int_offset(const struct btf_type *t)
+{
+	return BTF_INT_OFFSET(*(__u32 *)(t + 1));
+}
+
+static inline __u8 btf_int_bits(const struct btf_type *t)
+{
+	return BTF_INT_BITS(*(__u32 *)(t + 1));
+}
+
+static inline struct btf_array *btf_array(const struct btf_type *t)
+{
+	return (struct btf_array *)(t + 1);
+}
+
+static inline struct btf_enum *btf_enum(const struct btf_type *t)
+{
+	return (struct btf_enum *)(t + 1);
+}
+
+static inline struct btf_member *btf_members(const struct btf_type *t)
+{
+	return (struct btf_member *)(t + 1);
+}
+
+/* Get bit offset of a member with specified index. */
+static inline __u32 btf_member_bit_offset(const struct btf_type *t,
+					  __u32 member_idx)
+{
+	const struct btf_member *m = btf_members(t) + member_idx;
+	bool kflag = btf_kflag(t);
+
+	return kflag ? BTF_MEMBER_BIT_OFFSET(m->offset) : m->offset;
+}
+/*
+ * Get bitfield size of a member, assuming t is BTF_KIND_STRUCT or
+ * BTF_KIND_UNION. If member is not a bitfield, zero is returned.
+ */
+static inline __u32 btf_member_bitfield_size(const struct btf_type *t,
+					     __u32 member_idx)
+{
+	const struct btf_member *m = btf_members(t) + member_idx;
+	bool kflag = btf_kflag(t);
+
+	return kflag ? BTF_MEMBER_BITFIELD_SIZE(m->offset) : 0;
+}
+
+static inline struct btf_param *btf_params(const struct btf_type *t)
+{
+	return (struct btf_param *)(t + 1);
+}
+
+static inline struct btf_var *btf_var(const struct btf_type *t)
+{
+	return (struct btf_var *)(t + 1);
+}
+
+static inline struct btf_var_secinfo *
+btf_var_secinfos(const struct btf_type *t)
+{
+	return (struct btf_var_secinfo *)(t + 1);
+}
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif

tools/lib/bpf/libbpf.h

@@ -92,6 +92,7 @@ LIBBPF_API void bpf_object__close(struct bpf_object *object);
 struct bpf_object_load_attr {
 	struct bpf_object *obj;
 	int log_level;
+	const char *target_btf_path;
 };
 
 /* Load/unload object into/from kernel */

tools/lib/bpf/libbpf_internal.h

@@ -29,6 +29,10 @@
 #ifndef max
 # define max(x, y) ((x) < (y) ? (y) : (x))
 #endif
+#ifndef offsetofend
+# define offsetofend(TYPE, FIELD) \
+	(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))
+#endif
 
 extern void libbpf_print(enum libbpf_print_level level,
 			 const char *format, ...)
@@ -46,4 +50,105 @@ do {				\
 int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
 			 const char *str_sec, size_t str_len);
 
+struct btf_ext_info {
+	/*
+	 * info points to the individual info section (e.g. func_info and
+	 * line_info) from the .BTF.ext. It does not include the __u32 rec_size.
+	 */
+	void *info;
+	__u32 rec_size;
+	__u32 len;
+};
+
+#define for_each_btf_ext_sec(seg, sec)					\
+	for (sec = (seg)->info;						\
+	     (void *)sec < (seg)->info + (seg)->len;			\
+	     sec = (void *)sec + sizeof(struct btf_ext_info_sec) +	\
+		   (seg)->rec_size * sec->num_info)
+
+#define for_each_btf_ext_rec(seg, sec, i, rec)				\
+	for (i = 0, rec = (void *)&(sec)->data;				\
+	     i < (sec)->num_info;					\
+	     i++, rec = (void *)rec + (seg)->rec_size)
+
+struct btf_ext {
+	union {
+		struct btf_ext_header *hdr;
+		void *data;
+	};
+	struct btf_ext_info func_info;
+	struct btf_ext_info line_info;
+	struct btf_ext_info offset_reloc_info;
+	__u32 data_size;
+};
+
+struct btf_ext_info_sec {
+	__u32	sec_name_off;
+	__u32	num_info;
+	/* Followed by num_info * record_size number of bytes */
+	__u8	data[0];
+};
+
+/* The minimum bpf_func_info checked by the loader */
+struct bpf_func_info_min {
+	__u32   insn_off;
+	__u32   type_id;
+};
+
+/* The minimum bpf_line_info checked by the loader */
+struct bpf_line_info_min {
+	__u32	insn_off;
+	__u32	file_name_off;
+	__u32	line_off;
+	__u32	line_col;
+};
+
+/* The minimum bpf_offset_reloc checked by the loader
+ *
+ * Offset relocation captures the following data:
+ * - insn_off - instruction offset (in bytes) within a BPF program that needs
+ *   its insn->imm field to be relocated with actual offset;
+ * - type_id - BTF type ID of the "root" (containing) entity of a relocatable
+ *   offset;
+ * - access_str_off - offset into corresponding .BTF string section. String
+ *   itself encodes an accessed field using a sequence of field and array
+ *   indicies, separated by colon (:). It's conceptually very close to LLVM's
+ *   getelementptr ([0]) instruction's arguments for identifying offset to 
+ *   a field.
+ *
+ * Example to provide a better feel.
+ *
+ *   struct sample {
+ *       int a;
+ *       struct {
+ *           int b[10];
+ *       };
+ *   };
+ *
+ *   struct sample *s = ...;
+ *   int x = &s->a;     // encoded as "0:0" (a is field #0)
+ *   int y = &s->b[5];  // encoded as "0:1:0:5" (anon struct is field #1, 
+ *                      // b is field #0 inside anon struct, accessing elem #5)
+ *   int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
+ *
+ * type_id for all relocs in this example  will capture BTF type id of
+ * `struct sample`.
+ *
+ * Such relocation is emitted when using __builtin_preserve_access_index()
+ * Clang built-in, passing expression that captures field address, e.g.:
+ *
+ * bpf_probe_read(&dst, sizeof(dst),
+ *		  __builtin_preserve_access_index(&src->a.b.c));
+ *
+ * In this case Clang will emit offset relocation recording necessary data to
+ * be able to find offset of embedded `a.b.c` field within `src` struct.
+ *
+ *   [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
+ */
+struct bpf_offset_reloc {
+	__u32   insn_off;
+	__u32   type_id;
+	__u32   access_str_off;
+};
+
 #endif /* __LIBBPF_LIBBPF_INTERNAL_H */

tools/testing/selftests/bpf/bpf_helpers.h

@@ -504,4 +504,24 @@ struct pt_regs;
 				(void *)(PT_REGS_FP(ctx) + sizeof(ip))); })
 #endif
 
+/*
+ * BPF_CORE_READ abstracts away bpf_probe_read() call and captures offset
+ * relocation for source address using __builtin_preserve_access_index()
+ * built-in, provided by Clang.
+ *
+ * __builtin_preserve_access_index() takes as an argument an expression of
+ * taking an address of a field within struct/union. It makes compiler emit
+ * a relocation, which records BTF type ID describing root struct/union and an
+ * accessor string which describes exact embedded field that was used to take
+ * an address. See detailed description of this relocation format and
+ * semantics in comments to struct bpf_offset_reloc in libbpf_internal.h.
+ *
+ * This relocation allows libbpf to adjust BPF instruction to use correct
+ * actual field offset, based on target kernel BTF type that matches original
+ * (local) BTF, used to record relocation.
+ */
+#define BPF_CORE_READ(dst, src)						\
+	bpf_probe_read((dst), sizeof(*(src)),				\
+		       __builtin_preserve_access_index(src))
+
 #endif

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

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

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

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

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

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

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

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

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

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

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

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

tools/testing/selftests/bpf/progs/btf__core_reloc_arrays___err_wrong_val_type1.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_arrays___err_wrong_val_type1 x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_arrays___err_wrong_val_type2.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_arrays___err_wrong_val_type2 x) {}

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/btf__core_reloc_ints.c

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

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

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

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

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

tools/testing/selftests/bpf/progs/btf__core_reloc_ints___err_wrong_sz_16.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_ints___err_wrong_sz_16 x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_ints___err_wrong_sz_32.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_ints___err_wrong_sz_32 x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_ints___err_wrong_sz_64.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_ints___err_wrong_sz_64 x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_ints___err_wrong_sz_8.c

+#include "core_reloc_types.h"
+
+void f(struct core_reloc_ints___err_wrong_sz_8 x) {}

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

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

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

+#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/btf__core_reloc_mods.c

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

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

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

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

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

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

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

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

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

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

+#include "core_reloc_types.h"
+
+void f1(struct core_reloc_nesting___dup_compat_types x) {}
+void f2(struct core_reloc_nesting___dup_compat_types__2 x) {}
+void f3(struct core_reloc_nesting___dup_compat_types__3 x) {}

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

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

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

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

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

+#include "core_reloc_types.h"
+
+void f1(struct core_reloc_nesting___err_dup_incompat_types__1 x) {}
+void f2(struct core_reloc_nesting___err_dup_incompat_types__2 x) {}

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

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

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

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

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

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

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

+#include "core_reloc_types.h"
+
+void f1(struct core_reloc_nesting___err_partial_match_dups__a x) {}
+void f2(struct core_reloc_nesting___err_partial_match_dups__b x) {}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

tools/testing/selftests/bpf/progs/test_core_reloc_arrays.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_arrays_output {
+	int a2;
+	char b123;
+	int c1c;
+	int d00d;
+};
+
+struct core_reloc_arrays_substruct {
+	int c;
+	int d;
+};
+
+struct core_reloc_arrays {
+	int a[5];
+	char b[2][3][4];
+	struct core_reloc_arrays_substruct c[3];
+	struct core_reloc_arrays_substruct d[1][2];
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_arrays(void *ctx)
+{
+	struct core_reloc_arrays *in = (void *)&data.in;
+	struct core_reloc_arrays_output *out = (void *)&data.out;
+
+	/* in->a[2] */
+	if (BPF_CORE_READ(&out->a2, &in->a[2]))
+		return 1;
+	/* in->b[1][2][3] */
+	if (BPF_CORE_READ(&out->b123, &in->b[1][2][3]))
+		return 1;
+	/* in->c[1].c */
+	if (BPF_CORE_READ(&out->c1c, &in->c[1].c))
+		return 1;
+	/* in->d[0][0].d */
+	if (BPF_CORE_READ(&out->d00d, &in->d[0][0].d))
+		return 1;
+
+	return 0;
+}
+

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;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_ints.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_ints {
+	uint8_t		u8_field;
+	int8_t		s8_field;
+	uint16_t	u16_field;
+	int16_t		s16_field;
+	uint32_t	u32_field;
+	int32_t		s32_field;
+	uint64_t	u64_field;
+	int64_t		s64_field;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_ints(void *ctx)
+{
+	struct core_reloc_ints *in = (void *)&data.in;
+	struct core_reloc_ints *out = (void *)&data.out;
+
+	if (BPF_CORE_READ(&out->u8_field, &in->u8_field) ||
+	    BPF_CORE_READ(&out->s8_field, &in->s8_field) ||
+	    BPF_CORE_READ(&out->u16_field, &in->u16_field) ||
+	    BPF_CORE_READ(&out->s16_field, &in->s16_field) ||
+	    BPF_CORE_READ(&out->u32_field, &in->u32_field) ||
+	    BPF_CORE_READ(&out->s32_field, &in->s32_field) ||
+	    BPF_CORE_READ(&out->u64_field, &in->u64_field) ||
+	    BPF_CORE_READ(&out->s64_field, &in->s64_field))
+		return 1;
+
+	return 0;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_kernel.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 task_struct {
+	int pid;
+	int tgid;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_kernel(void *ctx)
+{
+	struct task_struct *task = (void *)bpf_get_current_task();
+	uint64_t pid_tgid = bpf_get_current_pid_tgid();
+	int pid, tgid;
+
+	if (BPF_CORE_READ(&pid, &task->pid) ||
+	    BPF_CORE_READ(&tgid, &task->tgid))
+		return 1;
+
+	/* validate pid + tgid matches */
+	data.out[0] = (((uint64_t)pid << 32) | tgid) == pid_tgid;
+
+	return 0;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_misc.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_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;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_mods.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_mods_output {
+	int a, b, c, d, e, f, g, h;
+};
+
+typedef const int int_t;
+typedef const char *char_ptr_t;
+typedef const int arr_t[7];
+
+struct core_reloc_mods_substruct {
+	int x;
+	int y;
+};
+
+typedef struct {
+	int x;
+	int y;
+} core_reloc_mods_substruct_t;
+
+struct core_reloc_mods {
+	int a;
+	int_t b;
+	char *c;
+	char_ptr_t d;
+	int e[3];
+	arr_t f;
+	struct core_reloc_mods_substruct g;
+	core_reloc_mods_substruct_t h;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_mods(void *ctx)
+{
+	struct core_reloc_mods *in = (void *)&data.in;
+	struct core_reloc_mods_output *out = (void *)&data.out;
+
+	if (BPF_CORE_READ(&out->a, &in->a) ||
+	    BPF_CORE_READ(&out->b, &in->b) ||
+	    BPF_CORE_READ(&out->c, &in->c) ||
+	    BPF_CORE_READ(&out->d, &in->d) ||
+	    BPF_CORE_READ(&out->e, &in->e[2]) ||
+	    BPF_CORE_READ(&out->f, &in->f[1]) ||
+	    BPF_CORE_READ(&out->g, &in->g.x) ||
+	    BPF_CORE_READ(&out->h, &in->h.y))
+		return 1;
+
+	return 0;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_nesting.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_nesting_substruct {
+	int a;
+};
+
+union core_reloc_nesting_subunion {
+	int b;
+};
+
+/* int a.a.a and b.b.b accesses */
+struct core_reloc_nesting {
+	union {
+		struct core_reloc_nesting_substruct a;
+	} a;
+	struct {
+		union core_reloc_nesting_subunion b;
+	} b;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_nesting(void *ctx)
+{
+	struct core_reloc_nesting *in = (void *)&data.in;
+	struct core_reloc_nesting *out = (void *)&data.out;
+
+	if (BPF_CORE_READ(&out->a.a.a, &in->a.a.a))
+		return 1;
+	if (BPF_CORE_READ(&out->b.b.b, &in->b.b.b))
+		return 1;
+
+	return 0;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_primitives.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;
+
+enum core_reloc_primitives_enum {
+	A = 0,
+	B = 1,
+};
+
+struct core_reloc_primitives {
+	char a;
+	int b;
+	enum core_reloc_primitives_enum c;
+	void *d;
+	int (*f)(const char *);
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_primitives(void *ctx)
+{
+	struct core_reloc_primitives *in = (void *)&data.in;
+	struct core_reloc_primitives *out = (void *)&data.out;
+
+	if (BPF_CORE_READ(&out->a, &in->a) ||
+	    BPF_CORE_READ(&out->b, &in->b) ||
+	    BPF_CORE_READ(&out->c, &in->c) ||
+	    BPF_CORE_READ(&out->d, &in->d) ||
+	    BPF_CORE_READ(&out->f, &in->f))
+		return 1;
+
+	return 0;
+}
+

tools/testing/selftests/bpf/progs/test_core_reloc_ptr_as_arr.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_ptr_as_arr {
+	int a;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_ptr_as_arr(void *ctx)
+{
+	struct core_reloc_ptr_as_arr *in = (void *)&data.in;
+	struct core_reloc_ptr_as_arr *out = (void *)&data.out;
+
+	if (BPF_CORE_READ(&out->a, &in[2].a))
+		return 1;
+
+	return 0;
+}
+