On Thu, 2021-02-18 at 21:41 -0800, Yonghong Song wrote: > > > On 2/18/21 6:25 PM, Ilya Leoshkevich wrote: > > Also document the expansion of the kind bitfield. > > > > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> > > --- > > Documentation/bpf/btf.rst | 17 +++++++++++++++-- > > 1 file changed, 15 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst > > index 44dc789de2b4..4f25c992d442 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 +453,18 @@ 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. > > I would be good to specify the allowed size in bytes 2, multiple of > 4. > currently we do not have a maximum value, maybe 128. have a float > type > something like 2^10 seems strange. I tried to write this all down and realized it's simpler to enumerate the allowed values: 2, 4, 8, 12 and 16. I don't think there are 32-byte floats on any of the architectures supported by the kernel.
