libbpf: add __arg_trusted and __arg_nullable tag macros

Add __arg_trusted to annotate global func args that accept trusted
PTR_TO_BTF_ID arguments.

Also add __arg_nullable to combine with __arg_trusted (and maybe other
tags in the future) to force global subprog itself (i.e., callee) to do
NULL checks, as opposed to default non-NULL semantics (and thus caller's
responsibility to ensure non-NULL values).
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240130000648.2144827-4-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/bpf_helpers.h

@@ -190,6 +190,8 @@ enum libbpf_tristate {
 
 #define __arg_ctx __attribute__((btf_decl_tag("arg:ctx")))
 #define __arg_nonnull __attribute((btf_decl_tag("arg:nonnull")))
+#define __arg_nullable __attribute((btf_decl_tag("arg:nullable")))
+#define __arg_trusted __attribute((btf_decl_tag("arg:trusted")))
 
 #ifndef ___bpf_concat
 #define ___bpf_concat(a, b) a ## b