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bpf: Document BTF_KIND_FLOAT in btf.rst 

Also document the expansion of the kind bitfield.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210226202256.116518-11-iii@linux.ibm.com
This commit is contained in:
Ilya Leoshkevich 2021-02-26 21:22:56 +01:00 committed by Alexei Starovoitov
parent 7999cf7df8
commit 6be6a0baff
1 changed files with 15 additions and 2 deletions
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17
Documentation/bpf/btf.rst
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@ -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_FUNC_PROTO 13 /* Function Proto */
#define BTF_KIND_VAR 14 /* Variable */ #define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */ #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. 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. ``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 /* "info" bits arrangement
* bits 0-15: vlen (e.g. # of struct's members) * bits 0-15: vlen (e.g. # of struct's members)
* bits 16-23: unused * bits 16-23: unused
* bits 24-27: kind (e.g. int, ptr, array...etc) * bits 24-28: kind (e.g. int, ptr, array...etc)
* bits 28-30: unused * bits 29-30: unused
* bit 31: kind_flag, currently used by * bit 31: kind_flag, currently used by
* struct, union and fwd * struct, union and fwd
*/ */
@ -452,6 +453,18 @@ map definition.
* ``offset``: the in-section offset of the variable * ``offset``: the in-section offset of the variable
* ``size``: the size of the variable in bytes * ``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 3. BTF Kernel API
***************** *****************