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b0588390db
Move CO-RE logic into separate file. The internal interface between libbpf and CO-RE is through bpf_core_apply_relo_insn() function and few structs defined in relo_core.h. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20210721000822.40958-5-alexei.starovoitov@gmail.com
101 lines
3.7 KiB
C
101 lines
3.7 KiB
C
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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/* Copyright (c) 2019 Facebook */
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#ifndef __RELO_CORE_H
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#define __RELO_CORE_H
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/* bpf_core_relo_kind encodes which aspect of captured field/type/enum value
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* has to be adjusted by relocations.
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*/
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enum bpf_core_relo_kind {
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BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
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BPF_FIELD_BYTE_SIZE = 1, /* field size in bytes */
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BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
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BPF_FIELD_SIGNED = 3, /* field signedness (0 - unsigned, 1 - signed) */
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BPF_FIELD_LSHIFT_U64 = 4, /* bitfield-specific left bitshift */
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BPF_FIELD_RSHIFT_U64 = 5, /* bitfield-specific right bitshift */
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BPF_TYPE_ID_LOCAL = 6, /* type ID in local BPF object */
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BPF_TYPE_ID_TARGET = 7, /* type ID in target kernel */
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BPF_TYPE_EXISTS = 8, /* type existence in target kernel */
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BPF_TYPE_SIZE = 9, /* type size in bytes */
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BPF_ENUMVAL_EXISTS = 10, /* enum value existence in target kernel */
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BPF_ENUMVAL_VALUE = 11, /* enum value integer value */
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};
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/* The minimum bpf_core_relo checked by the loader
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*
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* CO-RE relocation captures the following data:
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* - insn_off - instruction offset (in bytes) within a BPF program that needs
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* its insn->imm field to be relocated with actual field info;
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* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
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* type or field;
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* - access_str_off - offset into corresponding .BTF string section. String
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* interpretation depends on specific relocation kind:
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* - for field-based relocations, string encodes an accessed field using
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* a sequence of field and array indices, separated by colon (:). It's
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* conceptually very close to LLVM's getelementptr ([0]) instruction's
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* arguments for identifying offset to a field.
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* - for type-based relocations, strings is expected to be just "0";
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* - for enum value-based relocations, string contains an index of enum
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* value within its enum type;
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*
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* Example to provide a better feel.
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*
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* struct sample {
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* int a;
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* struct {
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* int b[10];
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* };
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* };
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*
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* struct sample *s = ...;
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* int x = &s->a; // encoded as "0:0" (a is field #0)
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* int y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
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* // b is field #0 inside anon struct, accessing elem #5)
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* int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
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*
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* type_id for all relocs in this example will capture BTF type id of
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* `struct sample`.
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*
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* Such relocation is emitted when using __builtin_preserve_access_index()
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* Clang built-in, passing expression that captures field address, e.g.:
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*
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* bpf_probe_read(&dst, sizeof(dst),
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* __builtin_preserve_access_index(&src->a.b.c));
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*
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* In this case Clang will emit field relocation recording necessary data to
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* be able to find offset of embedded `a.b.c` field within `src` struct.
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*
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* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
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*/
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struct bpf_core_relo {
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__u32 insn_off;
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__u32 type_id;
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__u32 access_str_off;
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enum bpf_core_relo_kind kind;
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};
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struct bpf_core_cand {
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const struct btf *btf;
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const struct btf_type *t;
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const char *name;
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__u32 id;
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};
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/* dynamically sized list of type IDs and its associated struct btf */
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struct bpf_core_cand_list {
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struct bpf_core_cand *cands;
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int len;
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};
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int bpf_core_apply_relo_insn(const char *prog_name,
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struct bpf_insn *insn, int insn_idx,
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const struct bpf_core_relo *relo, int relo_idx,
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const struct btf *local_btf,
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struct bpf_core_cand_list *cands);
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int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
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const struct btf *targ_btf, __u32 targ_id);
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size_t bpf_core_essential_name_len(const char *name);
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#endif
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