On 22/01/2025 02:53, Ihor Solodrai wrote:
> Add the following functions to libbpf API:
> * btf__add_type_attr()
> * btf__add_decl_attr()
>
> These functions allow to add to BTF the type tags and decl tags with
> info->kflag set to 1. The kflag indicates that the tag directly
> encodes an __attribute__ and not a normal tag.
>
> See Documentation/bpf/btf.rst changes for details on the semantics.
>
> Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxx>
need to sync include/uapi/linux/btf.h with
tools/include/uapi/linux/btf.h, but other than that
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> Documentation/bpf/btf.rst | 27 +++++++++--
> tools/include/uapi/linux/btf.h | 3 +-
same change needed to include/uapi/linux/btf.h too, right?
> tools/lib/bpf/btf.c | 87 +++++++++++++++++++++++++---------
> tools/lib/bpf/btf.h | 3 ++
> tools/lib/bpf/libbpf.map | 2 +
> 5 files changed, 93 insertions(+), 29 deletions(-)
>
> diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
> index 2478cef758f8..615ded7b2442 100644
> --- a/Documentation/bpf/btf.rst
> +++ b/Documentation/bpf/btf.rst
> @@ -102,8 +102,9 @@ Each type contains the following common data::
> * bits 24-28: kind (e.g. int, ptr, array...etc)
> * bits 29-30: unused
> * bit 31: kind_flag, currently used by
> - * struct, union, fwd, enum and enum64.
> - */
> + * struct, union, enum, fwd, enum64,
> + * DECL_TAG and TYPE_TAG
> + */
> __u32 info;
> /* "size" is used by INT, ENUM, STRUCT, UNION and ENUM64.
> * "size" tells the size of the type it is describing.
> @@ -478,7 +479,7 @@ No additional type data follow ``btf_type``.
>
> ``struct btf_type`` encoding requirement:
> * ``name_off``: offset to a non-empty string
> - * ``info.kind_flag``: 0
> + * ``info.kind_flag``: 0 or 1
> * ``info.kind``: BTF_KIND_DECL_TAG
> * ``info.vlen``: 0
> * ``type``: ``struct``, ``union``, ``func``, ``var`` or ``typedef``
> @@ -489,7 +490,6 @@ No additional type data follow ``btf_type``.
> __u32 component_idx;
> };
>
> -The ``name_off`` encodes btf_decl_tag attribute string.
> The ``type`` should be ``struct``, ``union``, ``func``, ``var`` or ``typedef``.
> For ``var`` or ``typedef`` type, ``btf_decl_tag.component_idx`` must be ``-1``.
> For the other three types, if the btf_decl_tag attribute is
> @@ -499,12 +499,21 @@ the attribute is applied to a ``struct``/``union`` member or
> a ``func`` argument, and ``btf_decl_tag.component_idx`` should be a
> valid index (starting from 0) pointing to a member or an argument.
>
> +If ``info.kind_flag`` is 0, then this is a normal decl tag, and the
> +``name_off`` encodes btf_decl_tag attribute string.
> +
> +If ``info.kind_flag`` is 1, then the decl tag represents an arbitrary
> +__attribute__. In this case, ``name_off`` encodes a string
> +representing the attribute-list of the attribute specifier. For
> +example, for an ``__attribute__((aligned(4)))`` the string's contents
> +is ``aligned(4)``.
> +
> 2.2.18 BTF_KIND_TYPE_TAG
> ~~~~~~~~~~~~~~~~~~~~~~~~
>
> ``struct btf_type`` encoding requirement:
> * ``name_off``: offset to a non-empty string
> - * ``info.kind_flag``: 0
> + * ``info.kind_flag``: 0 or 1
> * ``info.kind``: BTF_KIND_TYPE_TAG
> * ``info.vlen``: 0
> * ``type``: the type with ``btf_type_tag`` attribute
> @@ -522,6 +531,14 @@ type_tag, then zero or more const/volatile/restrict/typedef
> and finally the base type. The base type is one of
> int, ptr, array, struct, union, enum, func_proto and float types.
>
> +Similarly to decl tags, if the ``info.kind_flag`` is 0, then this is a
> +normal type tag, and the ``name_off`` encodes btf_type_tag attribute
> +string.
> +
> +If ``info.kind_flag`` is 1, then the type tag represents an arbitrary
> +__attribute__, and the ``name_off`` encodes a string representing the
> +attribute-list of the attribute specifier.
> +
> 2.2.19 BTF_KIND_ENUM64
> ~~~~~~~~~~~~~~~~~~~~~~
>
> diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
> index ec1798b6d3ff..d602c26a0c2a 100644
> --- a/tools/include/uapi/linux/btf.h
> +++ b/tools/include/uapi/linux/btf.h
> @@ -36,7 +36,8 @@ struct btf_type {
> * bits 24-28: kind (e.g. int, ptr, array...etc)
> * bits 29-30: unused
> * bit 31: kind_flag, currently used by
> - * struct, union, enum, fwd and enum64
> + * struct, union, enum, fwd, enum64,
> + * DECL_TAG and TYPE_TAG
> */
> __u32 info;
> /* "size" is used by INT, ENUM, STRUCT, UNION, DATASEC and ENUM64.
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 48c66f3a9200..df2808cee009 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -2090,7 +2090,7 @@ static int validate_type_id(int id)
> }
>
> /* generic append function for PTR, TYPEDEF, CONST/VOLATILE/RESTRICT */
> -static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref_type_id)
> +static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref_type_id, int kflag)
> {
> struct btf_type *t;
> int sz, name_off = 0;
> @@ -2113,7 +2113,7 @@ static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref
> }
>
> t->name_off = name_off;
> - t->info = btf_type_info(kind, 0, 0);
> + t->info = btf_type_info(kind, 0, kflag);
> t->type = ref_type_id;
>
> return btf_commit_type(btf, sz);
> @@ -2128,7 +2128,7 @@ static int btf_add_ref_kind(struct btf *btf, int kind, const char *name, int ref
> */
> int btf__add_ptr(struct btf *btf, int ref_type_id)
> {
> - return btf_add_ref_kind(btf, BTF_KIND_PTR, NULL, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_PTR, NULL, ref_type_id, 0);
> }
>
> /*
> @@ -2506,7 +2506,7 @@ int btf__add_fwd(struct btf *btf, const char *name, enum btf_fwd_kind fwd_kind)
> struct btf_type *t;
> int id;
>
> - id = btf_add_ref_kind(btf, BTF_KIND_FWD, name, 0);
> + id = btf_add_ref_kind(btf, BTF_KIND_FWD, name, 0, 0);
> if (id <= 0)
> return id;
> t = btf_type_by_id(btf, id);
> @@ -2536,7 +2536,7 @@ int btf__add_typedef(struct btf *btf, const char *name, int ref_type_id)
> if (!name || !name[0])
> return libbpf_err(-EINVAL);
>
> - return btf_add_ref_kind(btf, BTF_KIND_TYPEDEF, name, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_TYPEDEF, name, ref_type_id, 0);
> }
>
> /*
> @@ -2548,7 +2548,7 @@ int btf__add_typedef(struct btf *btf, const char *name, int ref_type_id)
> */
> int btf__add_volatile(struct btf *btf, int ref_type_id)
> {
> - return btf_add_ref_kind(btf, BTF_KIND_VOLATILE, NULL, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_VOLATILE, NULL, ref_type_id, 0);
> }
>
> /*
> @@ -2560,7 +2560,7 @@ int btf__add_volatile(struct btf *btf, int ref_type_id)
> */
> int btf__add_const(struct btf *btf, int ref_type_id)
> {
> - return btf_add_ref_kind(btf, BTF_KIND_CONST, NULL, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_CONST, NULL, ref_type_id, 0);
> }
>
> /*
> @@ -2572,7 +2572,7 @@ int btf__add_const(struct btf *btf, int ref_type_id)
> */
> int btf__add_restrict(struct btf *btf, int ref_type_id)
> {
> - return btf_add_ref_kind(btf, BTF_KIND_RESTRICT, NULL, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_RESTRICT, NULL, ref_type_id, 0);
> }
>
> /*
> @@ -2588,7 +2588,24 @@ int btf__add_type_tag(struct btf *btf, const char *value, int ref_type_id)
> if (!value || !value[0])
> return libbpf_err(-EINVAL);
>
> - return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, ref_type_id);
> + return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, ref_type_id, 0);
> +}
> +
> +/*
> + * Append new BTF_KIND_TYPE_TAG type with:
> + * - *value*, non-empty/non-NULL tag value;
> + * - *ref_type_id* - referenced type ID, it might not exist yet;
> + * Set info->kflag to 1, indicating this tag is an __attribute__
> + * Returns:
> + * - >0, type ID of newly added BTF type;
> + * - <0, on error.
> + */
> +int btf__add_type_attr(struct btf *btf, const char *value, int ref_type_id)
> +{
> + if (!value || !value[0])
> + return libbpf_err(-EINVAL);
> +
> + return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, ref_type_id, 1);
> }
>
> /*
> @@ -2610,7 +2627,7 @@ int btf__add_func(struct btf *btf, const char *name,
> linkage != BTF_FUNC_EXTERN)
> return libbpf_err(-EINVAL);
>
> - id = btf_add_ref_kind(btf, BTF_KIND_FUNC, name, proto_type_id);
> + id = btf_add_ref_kind(btf, BTF_KIND_FUNC, name, proto_type_id, 0);
> if (id > 0) {
> struct btf_type *t = btf_type_by_id(btf, id);
>
> @@ -2845,18 +2862,9 @@ int btf__add_datasec_var_info(struct btf *btf, int var_type_id, __u32 offset, __
> return 0;
> }
>
> -/*
> - * Append new BTF_KIND_DECL_TAG type with:
> - * - *value* - non-empty/non-NULL string;
> - * - *ref_type_id* - referenced type ID, it might not exist yet;
> - * - *component_idx* - -1 for tagging reference type, otherwise struct/union
> - * member or function argument index;
> - * Returns:
> - * - >0, type ID of newly added BTF type;
> - * - <0, on error.
> - */
> -int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
> - int component_idx)
> +
> +static int __btf__add_decl_tag(struct btf *btf, const char *value,
> + int ref_type_id, int component_idx, int kflag)
> {
> struct btf_type *t;
> int sz, value_off;
> @@ -2880,13 +2888,46 @@ int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
> return value_off;
>
> t->name_off = value_off;
> - t->info = btf_type_info(BTF_KIND_DECL_TAG, 0, false);
> + t->info = btf_type_info(BTF_KIND_DECL_TAG, 0, kflag);
> t->type = ref_type_id;
> btf_decl_tag(t)->component_idx = component_idx;
>
> return btf_commit_type(btf, sz);
> }
>
> +/*
> + * Append new BTF_KIND_DECL_TAG type with:
> + * - *value* - non-empty/non-NULL string;
> + * - *ref_type_id* - referenced type ID, it might not exist yet;
> + * - *component_idx* - -1 for tagging reference type, otherwise struct/union
> + * member or function argument index;
> + * Returns:
> + * - >0, type ID of newly added BTF type;
> + * - <0, on error.
> + */
> +int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
> + int component_idx)
> +{
> + return __btf__add_decl_tag(btf, value, ref_type_id, component_idx, 0);
> +}
> +
> +/*
> + * Append new BTF_KIND_DECL_TAG type with:
> + * - *value* - non-empty/non-NULL string;
> + * - *ref_type_id* - referenced type ID, it might not exist yet;
> + * - *component_idx* - -1 for tagging reference type, otherwise struct/union
> + * member or function argument index;
> + * Set info->kflag to 1, indicating this tag is an __attribute__
> + * Returns:
> + * - >0, type ID of newly added BTF type;
> + * - <0, on error.
> + */
> +int btf__add_decl_attr(struct btf *btf, const char *value, int ref_type_id,
> + int component_idx)
> +{
> + return __btf__add_decl_tag(btf, value, ref_type_id, component_idx, 1);
> +}
> +
> struct btf_ext_sec_info_param {
> __u32 off;
> __u32 len;
> diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
> index 47ee8f6ac489..1c969a530a3e 100644
> --- a/tools/lib/bpf/btf.h
> +++ b/tools/lib/bpf/btf.h
> @@ -227,6 +227,7 @@ LIBBPF_API int btf__add_volatile(struct btf *btf, int ref_type_id);
> LIBBPF_API int btf__add_const(struct btf *btf, int ref_type_id);
> LIBBPF_API int btf__add_restrict(struct btf *btf, int ref_type_id);
> LIBBPF_API int btf__add_type_tag(struct btf *btf, const char *value, int ref_type_id);
> +LIBBPF_API int btf__add_type_attr(struct btf *btf, const char *value, int ref_type_id);
>
> /* func and func_proto construction APIs */
> LIBBPF_API int btf__add_func(struct btf *btf, const char *name,
> @@ -243,6 +244,8 @@ LIBBPF_API int btf__add_datasec_var_info(struct btf *btf, int var_type_id,
> /* tag construction API */
> LIBBPF_API int btf__add_decl_tag(struct btf *btf, const char *value, int ref_type_id,
> int component_idx);
> +LIBBPF_API int btf__add_decl_attr(struct btf *btf, const char *value, int ref_type_id,
> + int component_idx);
>
> struct btf_dedup_opts {
> size_t sz;
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index a8b2936a1646..8616e10b3c1b 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -436,4 +436,6 @@ LIBBPF_1.6.0 {
> bpf_linker__add_buf;
> bpf_linker__add_fd;
> bpf_linker__new_fd;
> + btf__add_decl_attr;
> + btf__add_type_attr;
> } LIBBPF_1.5.0;
