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Diffstat (limited to 'Documentation/bpf/btf.rst')
| -rw-r--r-- | Documentation/bpf/btf.rst | 61 |
1 files changed, 60 insertions, 1 deletions
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index 7313d354f20e..35d83e24dbdb 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -82,6 +82,8 @@ sequentially and type id is assigned to each recognized type starting from id #define BTF_KIND_RESTRICT 11 /* Restrict */ #define BTF_KIND_FUNC 12 /* Function */ #define BTF_KIND_FUNC_PROTO 13 /* Function Proto */ + #define BTF_KIND_VAR 14 /* Variable */ + #define BTF_KIND_DATASEC 15 /* Section */ Note that the type section encodes debug info, not just pure types. ``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram. @@ -129,7 +131,7 @@ The following sections detail encoding of each kind. ``btf_type`` is followed by a ``u32`` with the following bits arrangement:: #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24) - #define BTF_INT_OFFSET(VAL) (((VAL & 0x00ff0000)) >> 16) + #define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16) #define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff) The ``BTF_INT_ENCODING`` has the following attributes:: @@ -393,6 +395,61 @@ refers to parameter type. If the function has variable arguments, the last parameter is encoded with ``name_off = 0`` and ``type = 0``. +2.2.14 BTF_KIND_VAR +~~~~~~~~~~~~~~~~~~~ + +``struct btf_type`` encoding requirement: + * ``name_off``: offset to a valid C identifier + * ``info.kind_flag``: 0 + * ``info.kind``: BTF_KIND_VAR + * ``info.vlen``: 0 + * ``type``: the type of the variable + +``btf_type`` is followed by a single ``struct btf_variable`` with the +following data:: + + struct btf_var { + __u32 linkage; + }; + +``struct btf_var`` encoding: + * ``linkage``: currently only static variable 0, or globally allocated + variable in ELF sections 1 + +Not all type of global variables are supported by LLVM at this point. +The following is currently available: + + * static variables with or without section attributes + * global variables with section attributes + +The latter is for future extraction of map key/value type id's from a +map definition. + +2.2.15 BTF_KIND_DATASEC +~~~~~~~~~~~~~~~~~~~~~~~ + +``struct btf_type`` encoding requirement: + * ``name_off``: offset to a valid name associated with a variable or + one of .data/.bss/.rodata + * ``info.kind_flag``: 0 + * ``info.kind``: BTF_KIND_DATASEC + * ``info.vlen``: # of variables + * ``size``: total section size in bytes (0 at compilation time, patched + to actual size by BPF loaders such as libbpf) + +``btf_type`` is followed by ``info.vlen`` number of ``struct btf_var_secinfo``.:: + + struct btf_var_secinfo { + __u32 type; + __u32 offset; + __u32 size; + }; + +``struct btf_var_secinfo`` encoding: + * ``type``: the type of the BTF_KIND_VAR variable + * ``offset``: the in-section offset of the variable + * ``size``: the size of the variable in bytes + 3. BTF Kernel API ***************** @@ -521,6 +578,7 @@ For line_info, the line number and column number are defined as below: #define BPF_LINE_INFO_LINE_COL(line_col) ((line_col) & 0x3ff) 3.4 BPF_{PROG,MAP}_GET_NEXT_ID +============================== In kernel, every loaded program, map or btf has a unique id. The id won't change during the lifetime of a program, map, or btf. @@ -530,6 +588,7 @@ each command, to user space, for bpf program or maps, respectively, so an inspection tool can inspect all programs and maps. 3.5 BPF_{PROG,MAP}_GET_FD_BY_ID +=============================== An introspection tool cannot use id to get details about program or maps. A file descriptor needs to be obtained first for reference-counting purpose. |