bpf: Extend BTF UAPI vlen, kinds to use unused bits

BTF maximum vlen is encoded using 16 bits with a maximum vlen
of 65535.  This has sufficed for structs, function parameters
and enumerated type values.  However, with upcoming BTF location
information - in particular information about inline sites -
this limit is surpassed.  Use bits 16-23 - currently unused in
BTF info - to extend to 24 bits, giving a max vlen of (2^24 - 1),
or 16 million.

Also extend BTF kind encoding from 5 to 7 bits, giving a maximum
available number of kinds of 128.  Since with the BTF location work
we use another 3 kinds, we are fast approaching the current limit
of 32.

Convert BTF_MAX_* values to enums to allow them to be encoded in
kernel BTF; this will allow us to detect if the running kernel
supports a 24-bit vlen or not.  Add one for max _possible_
(not used) kind.

Fix up a few places in the kernel where a 16-bit vlen is assumed;
remove BTF_INFO_MASK as now all bits are used.

The vlen expansion was suggested by Andrii in [1]; the kind expansion
is tackled here too as it may be needed also to support new kinds
in BTF.

[1] https://lore.kernel.org/bpf/CAEf4BzZx=X6vGqcA8SPU6D+v6k+TR=ZewebXMuXtpmML058piw@mail.gmail.com/

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://lore.kernel.org/r/20260417143023.1551481-2-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 48108471c5b1..c82d0d689059 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -415,12 +415,12 @@ static inline bool btf_type_is_array(const struct btf_type *t)
 	return BTF_INFO_KIND(t->info) == BTF_KIND_ARRAY;
 }
 
-static inline u16 btf_type_vlen(const struct btf_type *t)
+static inline u32 btf_type_vlen(const struct btf_type *t)
 {
 	return BTF_INFO_VLEN(t->info);
 }
 
-static inline u16 btf_vlen(const struct btf_type *t)
+static inline u32 btf_vlen(const struct btf_type *t)
 {
 	return btf_type_vlen(t);
 }