On Sat, May 9, 2020 at 10:19 PM Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 5/9/20 5:50 PM, Alexei Starovoitov wrote:
> > On Sat, May 09, 2020 at 10:59:12AM -0700, Yonghong Song wrote:
> >> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> >> index a2cfba89a8e1..c490fbde22d4 100644
> >> --- a/kernel/bpf/btf.c
> >> +++ b/kernel/bpf/btf.c
> >> @@ -3790,7 +3790,10 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> >> return true;
> >>
> >> /* this is a pointer to another type */
> >> - info->reg_type = PTR_TO_BTF_ID;
> >> + if (off != 0 && prog->aux->btf_id_or_null_non0_off)
> >> + info->reg_type = PTR_TO_BTF_ID_OR_NULL;
> >> + else
> >> + info->reg_type = PTR_TO_BTF_ID;
> >
> > I think the verifier should be smarter than this.
> > It's too specific and inflexible. All ctx fields of bpf_iter execpt first
> > will be such ? let's figure out a different way to tell verifier about this.
> > How about using typedef with specific suffix? Like:
> > typedef struct bpf_map *bpf_map_or_null;
> > struct bpf_iter__bpf_map {
> > struct bpf_iter_meta *meta;
> > bpf_map_or_null map;
> > };
> > or use a union with specific second member? Like:
> > struct bpf_iter__bpf_map {
> > struct bpf_iter_meta *meta;
> > union {
> > struct bpf_map *map;
> > long null;
> > };
> > };
>
> I have an alternative approach to refactor this for future
> support for map elements as well.
>
> For example, for bpf_map_elements iterator the prog context type
> can be
> struct bpf_iter_bpf_map_elem {
> struct bpf_iter_meta *meta;
> strruct bpf_map *map;
> <key type> *key;
> <value type> *val;
> };
>
> target will pass the following information to bpf_iter registration:
> arg 1: PTR_TO_BTF_ID
> arg 2: PTR_TO_BTF_ID_OR_NULL
> arg 3: PTR_TO_BUFFER
> arg 4: PTR_TO_BUFFER
>
> verifier will retrieve the reg_type from target.
you mean to introduce something like 'struct bpf_func_proto'
that describes types of helpers, but instead something similar
to clarify the types in ctx ? That should work. Thanks
