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bpf: Support for new btf kind BTF_KIND_TAG

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LLVM14 added support for a new C attribute ([1])
  __attribute__((btf_tag("arbitrary_str")))
This attribute will be emitted to dwarf ([2]) and pahole
will convert it to BTF. Or for bpf target, this
attribute will be emitted to BTF directly ([3], [4]).
The attribute is intended to provide additional
information for
  - struct/union type or struct/union member
  - static/global variables
  - static/global function or function parameter.

For linux kernel, the btf_tag can be applied
in various places to specify user pointer,
function pre- or post- condition, function
allow/deny in certain context, etc. Such information
will be encoded in vmlinux BTF and can be used
by verifier.

The btf_tag can also be applied to bpf programs
to help global verifiable functions, e.g.,
specifying preconditions, etc.

This patch added basic parsing and checking support
in kernel for new BTF_KIND_TAG kind.

 [1] https://reviews.llvm.org/D106614
 [2] https://reviews.llvm.org/D106621
 [3] https://reviews.llvm.org/D106622
 [4] https://reviews.llvm.org/D109560

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210914223015.245546-1-yhs@fb.com
This commit is contained in:
Yonghong Song
2021-09-14 15:30:15 -07:00
committed by Alexei Starovoitov
parent 41ced4cd88
commit b5ea834dde
3 changed files with 154 additions and 2 deletions
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14
include/uapi/linux/btf.h
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@@ -43,7 +43,7 @@ struct btf_type {
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
* FUNC, FUNC_PROTO and VAR.
* FUNC, FUNC_PROTO, VAR and TAG.
* "type" is a type_id referring to another type.
*/
union {
@@ -74,6 +74,7 @@ enum {
BTF_KIND_VAR = 14, /* Variable */
BTF_KIND_DATASEC = 15, /* Section */
BTF_KIND_FLOAT = 16, /* Floating point */
BTF_KIND_TAG = 17, /* Tag */
NR_BTF_KINDS,
BTF_KIND_MAX = NR_BTF_KINDS - 1,
@@ -173,4 +174,15 @@ struct btf_var_secinfo {
__u32 size;
};
/* BTF_KIND_TAG is followed by a single "struct btf_tag" to describe
* additional information related to the tag applied location.
* If component_idx == -1, the tag is applied to a struct, union,
* variable or function. Otherwise, it is applied to a struct/union
* member or a func argument, and component_idx indicates which member
* or argument (0 ... vlen-1).
*/
struct btf_tag {
__s32 component_idx;
};
#endif /* _UAPI__LINUX_BTF_H__ */