BTF kind layouts provide information to parse BTF kinds. By separating parsing BTF from using all the information it provides, we allow BTF to encode new features even if they cannot be used. This is helpful in particular for cases where newer tools for BTF generation run on an older kernel; BTF kinds may be present that the kernel cannot yet use, but at least it can parse the BTF provided. Meanwhile userspace tools with newer libbpf may be able to use the newer information. The intent is to support encoding of kind layouts optionally so that tools like pahole can add this information. So for each kind we record - kind-related flags - length of singular element following struct btf_type - length of each of the btf_vlen() elements following In addition we make space in the BTF header for CRC32s computed over the BTF along with a CRC for the base BTF; this allows split BTF to identify a mismatch explicitly. The ideas here were discussed at [1], [2]; hence Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx> [1] https://lore.kernel.org/bpf/CAEf4BzYjWHRdNNw4B=eOXOs_ONrDwrgX4bn=Nuc1g8JPFC34MA@xxxxxxxxxxxxxx/ [2] https://lore.kernel.org/bpf/20230531201936.1992188-1-alan.maguire@xxxxxxxxxx/ --- include/uapi/linux/btf.h | 18 ++++++++++++++++++ tools/include/uapi/linux/btf.h | 18 ++++++++++++++++++ 2 files changed, 36 insertions(+) diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h index ec1798b6d3ff..5cc8cc793cd2 100644 --- a/include/uapi/linux/btf.h +++ b/include/uapi/linux/btf.h @@ -8,6 +8,19 @@ #define BTF_MAGIC 0xeB9F #define BTF_VERSION 1 +/* kind layout section consists of a struct btf_kind_layout for each known + * kind at BTF encoding time. + */ +struct btf_kind_layout { + __u16 flags; /* currently unused */ + __u8 info_sz; /* size of singular element after btf_type */ + __u8 elem_sz; /* size of each of btf_vlen(t) elements */ +}; + +/* for CRCs for BTF, base BTF to be considered usable, flags must be set. */ +#define BTF_FLAG_CRC_SET (1 << 0) +#define BTF_FLAG_BASE_CRC_SET (1 << 1) + struct btf_header { __u16 magic; __u8 version; @@ -19,6 +32,11 @@ struct btf_header { __u32 type_len; /* length of type section */ __u32 str_off; /* offset of string section */ __u32 str_len; /* length of string section */ + __u32 kind_layout_off;/* offset of kind layout section */ + __u32 kind_layout_len;/* length of kind layout section */ + + __u32 crc; /* crc of BTF; used if flags set BTF_FLAG_CRC_SET */ + __u32 base_crc; /* crc of base BTF; used if flags set BTF_FLAG_BASE_CRC_SET */ }; /* Max # of type identifier */ diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h index ec1798b6d3ff..5cc8cc793cd2 100644 --- a/tools/include/uapi/linux/btf.h +++ b/tools/include/uapi/linux/btf.h @@ -8,6 +8,19 @@ #define BTF_MAGIC 0xeB9F #define BTF_VERSION 1 +/* kind layout section consists of a struct btf_kind_layout for each known + * kind at BTF encoding time. + */ +struct btf_kind_layout { + __u16 flags; /* currently unused */ + __u8 info_sz; /* size of singular element after btf_type */ + __u8 elem_sz; /* size of each of btf_vlen(t) elements */ +}; + +/* for CRCs for BTF, base BTF to be considered usable, flags must be set. */ +#define BTF_FLAG_CRC_SET (1 << 0) +#define BTF_FLAG_BASE_CRC_SET (1 << 1) + struct btf_header { __u16 magic; __u8 version; @@ -19,6 +32,11 @@ struct btf_header { __u32 type_len; /* length of type section */ __u32 str_off; /* offset of string section */ __u32 str_len; /* length of string section */ + __u32 kind_layout_off;/* offset of kind layout section */ + __u32 kind_layout_len;/* length of kind layout section */ + + __u32 crc; /* crc of BTF; used if flags set BTF_FLAG_CRC_SET */ + __u32 base_crc; /* crc of base BTF; used if flags set BTF_FLAG_BASE_CRC_SET */ }; /* Max # of type identifier */ -- 2.31.1
