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| author | Eduard Zingerman <eddyz87@gmail.com> | 2023-08-27 01:29:12 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2023-08-30 09:53:02 +0200 |
| commit | be4033d36070e44fba766a21ef2d0c24fa04c377 (patch) | |
| tree | f4c6650555e8c775e3d40cdacdc3599225984d50 /Documentation/bpf/btf.rst | |
| parent | 2d71a90f7e0fa3cd348602a36f6eb1237ab7cebb (diff) | |
docs/bpf: Add description for CO-RE relocations
Add a section on CO-RE relocations to llvm_relo.rst. Describe relevant .BTF.ext
structure, `enum bpf_core_relo_kind` and `struct bpf_core_relo` in some detail.
Description is based on doc-strings from:
- include/uapi/linux/bpf.h:struct bpf_core_relo
- tools/lib/bpf/relo_core.c:__bpf_core_types_match()
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20230826222912.2560865-2-eddyz87@gmail.com
Diffstat (limited to 'Documentation/bpf/btf.rst')
| -rw-r--r-- | Documentation/bpf/btf.rst | 31 |
1 files changed, 25 insertions, 6 deletions
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index f32db1f44ae9..ffc11afee569 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -726,8 +726,8 @@ same as the one describe in :ref:`BTF_Type_String`. 4.2 .BTF.ext section -------------------- -The .BTF.ext section encodes func_info and line_info which needs loader -manipulation before loading into the kernel. +The .BTF.ext section encodes func_info, line_info and CO-RE relocations +which needs loader manipulation before loading into the kernel. The specification for .BTF.ext section is defined at ``tools/lib/bpf/btf.h`` and ``tools/lib/bpf/btf.c``. @@ -745,15 +745,20 @@ The current header of .BTF.ext section:: __u32 func_info_len; __u32 line_info_off; __u32 line_info_len; + + /* optional part of .BTF.ext header */ + __u32 core_relo_off; + __u32 core_relo_len; }; It is very similar to .BTF section. Instead of type/string section, it -contains func_info and line_info section. See :ref:`BPF_Prog_Load` for details -about func_info and line_info record format. +contains func_info, line_info and core_relo sub-sections. +See :ref:`BPF_Prog_Load` for details about func_info and line_info +record format. The func_info is organized as below.:: - func_info_rec_size + func_info_rec_size /* __u32 value */ btf_ext_info_sec for section #1 /* func_info for section #1 */ btf_ext_info_sec for section #2 /* func_info for section #2 */ ... @@ -773,7 +778,7 @@ Here, num_info must be greater than 0. The line_info is organized as below.:: - line_info_rec_size + line_info_rec_size /* __u32 value */ btf_ext_info_sec for section #1 /* line_info for section #1 */ btf_ext_info_sec for section #2 /* line_info for section #2 */ ... @@ -787,6 +792,20 @@ kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the beginning of section (``btf_ext_info_sec->sec_name_off``). +The core_relo is organized as below.:: + + core_relo_rec_size /* __u32 value */ + btf_ext_info_sec for section #1 /* core_relo for section #1 */ + btf_ext_info_sec for section #2 /* core_relo for section #2 */ + +``core_relo_rec_size`` specifies the size of ``bpf_core_relo`` +structure when .BTF.ext is generated. All ``bpf_core_relo`` structures +within a single ``btf_ext_info_sec`` describe relocations applied to +section named by ``btf_ext_info_sec->sec_name_off``. + +See :ref:`Documentation/bpf/llvm_reloc <btf-co-re-relocations>` +for more information on CO-RE relocations. + 4.2 .BTF_ids section -------------------- |