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docs/bpf: Update documentation for BTF_KIND_ENUM64 support 

Add BTF_KIND_ENUM64 documentation in btf.rst.
Also fixed a typo for section number for BTF_KIND_TYPE_TAG
from 2.2.17 to 2.2.18, and fixed a type size issue for
BTF_KIND_ENUM.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220607062724.3728215-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2022-06-06 23:27:24 -07:00 committed by Alexei Starovoitov
parent f4db3dd528
commit 61dbd59829
1 changed files with 37 additions and 6 deletions
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43
Documentation/bpf/btf.rst
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@ -74,7 +74,7 @@ sequentially and type id is assigned to each recognized type starting from id
#define BTF_KIND_ARRAY 3 /* Array */
#define BTF_KIND_STRUCT 4 /* Struct */
#define BTF_KIND_UNION 5 /* Union */
#define BTF_KIND_ENUM 6 /* Enumeration */
#define BTF_KIND_ENUM 6 /* Enumeration up to 32-bit values */
#define BTF_KIND_FWD 7 /* Forward */
#define BTF_KIND_TYPEDEF 8 /* Typedef */
#define BTF_KIND_VOLATILE 9 /* Volatile */
@ -87,6 +87,7 @@ sequentially and type id is assigned to each recognized type starting from id
#define BTF_KIND_FLOAT 16 /* Floating point */
#define BTF_KIND_DECL_TAG 17 /* Decl Tag */
#define BTF_KIND_TYPE_TAG 18 /* Type Tag */
#define BTF_KIND_ENUM64 19 /* Enumeration up to 64-bit values */
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.
@ -101,10 +102,10 @@ 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 and fwd
* struct, union, fwd, enum and enum64.
*/
__u32 info;
/* "size" is used by INT, ENUM, STRUCT and UNION.
/* "size" is used by INT, ENUM, STRUCT, UNION and ENUM64.
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
@ -281,10 +282,10 @@ modes exist:
``struct btf_type`` encoding requirement:
* ``name_off``: 0 or offset to a valid C identifier
* ``info.kind_flag``: 0
* ``info.kind_flag``: 0 for unsigned, 1 for signed
* ``info.kind``: BTF_KIND_ENUM
* ``info.vlen``: number of enum values
* ``size``: 4
* ``size``: 1/2/4/8
``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum``.::
@ -297,6 +298,10 @@ The ``btf_enum`` encoding:
* ``name_off``: offset to a valid C identifier
* ``val``: any value
If the original enum value is signed and the size is less than 4,
that value will be sign extended into 4 bytes. If the size is 8,
the value will be truncated into 4 bytes.
2.2.7 BTF_KIND_FWD
~~~~~~~~~~~~~~~~~~
@ -493,7 +498,7 @@ 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.
2.2.17 BTF_KIND_TYPE_TAG
2.2.18 BTF_KIND_TYPE_TAG
~~~~~~~~~~~~~~~~~~~~~~~~
``struct btf_type`` encoding requirement:
@ -516,6 +521,32 @@ 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.
2.2.19 BTF_KIND_ENUM64
~~~~~~~~~~~~~~~~~~~~~~
``struct btf_type`` encoding requirement:
* ``name_off``: 0 or offset to a valid C identifier
* ``info.kind_flag``: 0 for unsigned, 1 for signed
* ``info.kind``: BTF_KIND_ENUM64
* ``info.vlen``: number of enum values
* ``size``: 1/2/4/8
``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum64``.::
struct btf_enum64 {
__u32 name_off;
__u32 val_lo32;
__u32 val_hi32;
};
The ``btf_enum64`` encoding:
* ``name_off``: offset to a valid C identifier
* ``val_lo32``: lower 32-bit value for a 64-bit value
* ``val_hi32``: high 32-bit value for a 64-bit value
If the original enum value is signed and the size is less than 8,
that value will be sign extended into 8 bytes.
3. BTF Kernel API
=================