Commit 6be6a0ba authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Alexei Starovoitov
Browse files

bpf: Document BTF_KIND_FLOAT in btf.rst 



Also document the expansion of the kind bitfield.

Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210226202256.116518-11-iii@linux.ibm.com
parent 7999cf7d

Documentation/bpf/btf.rst

+15 −2
Original line number Diff line number Diff line
@@ -84,6 +84,7 @@ sequentially and type id is assigned to each recognized type starting from id 
    #define BTF_KIND_FUNC_PROTO     13      /* Function Proto       */

    #define BTF_KIND_VAR            14      /* Variable     */

    #define BTF_KIND_DATASEC        15      /* Section      */

    #define BTF_KIND_FLOAT          16      /* Floating point       */



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.
@@ -95,8 +96,8 @@ Each type contains the following common data:: 
        /* "info" bits arrangement

         * bits  0-15: vlen (e.g. # of struct's members)

         * bits 16-23: unused

         * bits 24-27: kind (e.g. int, ptr, array...etc)

         * bits 28-30: unused

         * 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

         */
@@ -452,6 +453,18 @@ map definition. 
  * ``offset``: the in-section offset of the variable

  * ``size``: the size of the variable in bytes



2.2.16 BTF_KIND_FLOAT

~~~~~~~~~~~~~~~~~~~~~



``struct btf_type`` encoding requirement:

 * ``name_off``: any valid offset

 * ``info.kind_flag``: 0

 * ``info.kind``: BTF_KIND_FLOAT

 * ``info.vlen``: 0

 * ``size``: the size of the float type in bytes: 2, 4, 8, 12 or 16.



No additional type data follow ``btf_type``.



3. BTF Kernel API

*****************