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[RFC,6/6] bpf: Document BTF_KIND_FLOAT in btf.rst

Message ID 20210210030317.78820-7-iii@linux.ibm.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Add BTF_KIND_FLOAT support | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Ilya Leoshkevich Feb. 10, 2021, 3:03 a.m. UTC 
The description is based on BTF_KIND_INT. Also document the expansion
of the kind bitfield.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 Documentation/bpf/btf.rst | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)
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Patch

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 44dc789de2b4..d1d88d3a5d3f 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -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 +453,20 @@  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.
+
+``btf_type`` is followed by a ``u32`` with the following bits arrangement::
+
+  #define BTF_FLOAT_BITS(VAL)     ((VAL)  & 0x000000ff)
+
 3. BTF Kernel API
 *****************