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bpf: add specification for BTF Var and DataSec kinds 

This adds the BTF specification and UAPI bits for supporting BTF Var
and DataSec kinds. This is following LLVM upstream commit ac4082b77e07
("[BPF] Add BTF Var and DataSec Support") which has been merged recently.
Var itself is for describing a global variable and DataSec to describe
ELF sections e.g. data/bss/rodata sections that hold one or multiple
global variables.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2019-04-09 23:20:08 +02:00 committed by Alexei Starovoitov
parent 3e0ddc4f3f
commit f063c889c9
2 changed files with 85 additions and 4 deletions
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57
Documentation/bpf/btf.rst
View File

@ -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
*****************

32
include/uapi/linux/btf.h
View File

@ -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__ */