bpf: add specification for BTF Var and DataSec kinds (f063c889) · Commits · 戴 / test

Documentation/bpf/btf.rst

+57 −0

Original line number	Diff line number	Diff line
		@@ -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.
		@@ -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
		*****************

include/uapi/linux/btf.h

+28 −4

Original line number	Diff line number	Diff line
		@@ -39,11 +39,11 @@ struct btf_type {
		* struct, union and fwd
		*/
		__u32 info;
		/* "size" is used by INT, ENUM, STRUCT and UNION.
		/* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC.
		* "size" tells the size of the type it is describing.
		*
		* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
		* FUNC and FUNC_PROTO.
		* FUNC, FUNC_PROTO and VAR.
		* "type" is a type_id referring to another type.
		*/
		union {
		@@ -70,8 +70,10 @@ struct btf_type {
		#define BTF_KIND_RESTRICT 11 /* Restrict */
		#define BTF_KIND_FUNC 12 /* Function */
		#define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
		#define BTF_KIND_MAX 13
		#define NR_BTF_KINDS 14
		#define BTF_KIND_VAR 14 /* Variable */
		#define BTF_KIND_DATASEC 15 /* Section */
		#define BTF_KIND_MAX BTF_KIND_DATASEC
		#define NR_BTF_KINDS (BTF_KIND_MAX + 1)

		/* For some specific BTF_KIND, "struct btf_type" is immediately
		* followed by extra data.
		@@ -138,4 +140,26 @@ struct btf_param {
		__u32 type;
		};

		enum {
		BTF_VAR_STATIC = 0,
		BTF_VAR_GLOBAL_ALLOCATED,
		};

		/* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
		* additional information related to the variable such as its linkage.
		*/
		struct btf_var {
		__u32 linkage;
		};

		/* BTF_KIND_DATASEC is followed by multiple "struct btf_var_secinfo"
		* to describe all BTF_KIND_VAR types it contains along with it's
		* in-section offset as well as size.
		*/
		struct btf_var_secinfo {
		__u32 type;
		__u32 offset;
		__u32 size;
		};

		#endif /* _UAPI__LINUX_BTF_H__ */

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