Re: [External] Re: [PATCH bpf-next 1/5] bpf: tracing: add support to record and check the accessed args

[梦龙董 <dongmenglong.8@bytedance.com>]

On Wed, Feb 21, 2024 at 1:18 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Tue, Feb 20, 2024 at 11:51:01AM +0800, Menglong Dong wrote:
>
> SNIP
>
> > +static int get_ctx_arg_idx_aligned(struct btf *btf, const struct btf_type *t,
> > +                                int off)
> > +{
> > +     const struct btf_param *args;
> > +     u32 offset = 0, nr_args;
> > +     int i;
> > +
> > +     nr_args = btf_type_vlen(t);
> > +     args = (const struct btf_param *)(t + 1);
> > +     for (i = 0; i < nr_args; i++) {
> > +             if (offset == off)
> > +                     return i;
> > +
> > +             t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > +             offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> > +             if (offset > off)
> > +                     return -1;
> > +     }
> > +     return -1;
> > +}
> > +
> > +/* This function is similar to btf_check_func_type_match(), except that it
> > + * only compare some function args of the function prototype t1 and t2.
> > + */
>
> could we reuse btf_check_func_type_match instead? perhaps just
> adding extra argument with arguments bitmap to it?
>

This is a little difficult, as the way we check the consistency of t1
and t2 is a little different.

in btf_check_func_type_match(), we check the args of t1 and t2
by index. But in btf_check_func_part_match(), we check the args
of t1 and t2 by offset. Reusing can make btf_check_func_type_match
become complex and hard to understand.

Anyway, let me have a try to see if it works to reuse
btf_check_func_type_match().

Thanks!
Menglong Dong

> jirka
>
> > +int btf_check_func_part_match(struct btf *btf1, const struct btf_type *func1,
> > +                           struct btf *btf2, const struct btf_type *func2,
> > +                           u64 func_args)
> > +{
> > +     const struct btf_param *args1, *args2;
> > +     u32 nargs1, i, offset = 0;
> > +     const char *s1, *s2;
> > +
> > +     if (!btf_type_is_func_proto(func1) || !btf_type_is_func_proto(func2))
> > +             return -EINVAL;
> > +
> > +     args1 = (const struct btf_param *)(func1 + 1);
> > +     args2 = (const struct btf_param *)(func2 + 1);
> > +     nargs1 = btf_type_vlen(func1);
> > +
> > +     for (i = 0; i <= nargs1; i++) {
> > +             const struct btf_type *t1, *t2;
> > +
> > +             if (!(func_args & (1 << i)))
> > +                     goto next;
> > +
> > +             if (i < nargs1) {
> > +                     int t2_index;
> > +
> > +                     /* get the index of the arg corresponding to args1[i]
> > +                      * by the offset.
> > +                      */
> > +                     t2_index = get_ctx_arg_idx_aligned(btf2, func2,
> > +                                                        offset);
> > +                     if (t2_index < 0)
> > +                             return -EINVAL;
> > +
> > +                     t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
> > +                     t2 = btf_type_skip_modifiers(btf2, args2[t2_index].type,
> > +                                                  NULL);
> > +             } else {
> > +                     /* i == nargs1, this is the index of return value of t1 */
> > +                     if (get_ctx_arg_total_size(btf1, func1) !=
> > +                         get_ctx_arg_total_size(btf2, func2))
> > +                             return -EINVAL;
> > +
> > +                     /* check the return type of t1 and t2 */
> > +                     t1 = btf_type_skip_modifiers(btf1, func1->type, NULL);
> > +                     t2 = btf_type_skip_modifiers(btf2, func2->type, NULL);
> > +             }
> > +
> > +             if (t1->info != t2->info ||
> > +                 (btf_type_has_size(t1) && t1->size != t2->size))
> > +                     return -EINVAL;
> > +             if (btf_type_is_int(t1) || btf_is_any_enum(t1))
> > +                     goto next;
> > +
> > +             if (btf_type_is_struct(t1))
> > +                     goto on_struct;
> > +
> > +             if (!btf_type_is_ptr(t1))
> > +                     return -EINVAL;
> > +
> > +             t1 = btf_type_skip_modifiers(btf1, t1->type, NULL);
> > +             t2 = btf_type_skip_modifiers(btf2, t2->type, NULL);
> > +             if (!btf_type_is_struct(t1) || !btf_type_is_struct(t2))
> > +                     return -EINVAL;
> > +
> > +on_struct:
> > +             s1 = btf_name_by_offset(btf1, t1->name_off);
> > +             s2 = btf_name_by_offset(btf2, t2->name_off);
> > +             if (strcmp(s1, s2))
> > +                     return -EINVAL;
> > +next:
> > +             if (i < nargs1) {
> > +                     t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
> > +                     offset += btf_type_is_ptr(t1) ? 8 : roundup(t1->size, 8);
> > +             }
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> >  static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
> >  {
> >       const char *name;
> > --
> > 2.39.2
> >