On Fri, Feb 12, 2021 at 06:09:37PM -0800, Alexei Starovoitov wrote:
> On Sat, Feb 13, 2021 at 12:56:41AM +0400, Dmitrii Banshchikov wrote:
> > Add an ability to pass a pointer to a type with known size in arguments
> > of a global function. Such pointers may be used to overcome the limit on
> > the maximum number of arguments, avoid expensive and tricky workarounds
> > and to have multiple output arguments.
>
> Thanks a lot for adding this feature and exhaustive tests.
> It's a massive improvement in function-by-function verification.
> Hopefully it will increase its adoption.
> I've applied the set to bpf-next.
>
> > @@ -5349,10 +5352,6 @@ int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
> > goto out;
> > }
> > if (btf_type_is_ptr(t)) {
> > - if (reg->type == SCALAR_VALUE) {
> > - bpf_log(log, "R%d is not a pointer\n", i + 1);
> > - goto out;
> > - }
>
> Thanks for nuking this annoying warning along the way.
> People complained that the verification log for normal static functions
> contains above inexplicable message.
>
> > /* If function expects ctx type in BTF check that caller
> > * is passing PTR_TO_CTX.
> > */
> > @@ -5367,6 +5366,25 @@ int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
> > goto out;
> > continue;
> > }
> > +
> > + if (!is_global)
> > + goto out;
> > +
> > + t = btf_type_skip_modifiers(btf, t->type, NULL);
> > +
> > + ref_t = btf_resolve_size(btf, t, &type_size);
> > + if (IS_ERR(ref_t)) {
> > + bpf_log(log,
> > + "arg#%d reference type('%s %s') size cannot be determined: %ld\n",
> > + i, btf_type_str(t), btf_name_by_offset(btf, t->name_off),
> > + PTR_ERR(ref_t));
>
> Hopefully one annoying message won't get replaced with this annoying message :)
> I think the type size should be known most of the time. So it should be fine.
>
> > + if (btf_type_is_ptr(t)) {
> > + if (btf_get_prog_ctx_type(log, btf, t, prog_type, i)) {
> > + reg->type = PTR_TO_CTX;
> > + continue;
> > + }
>
> Do you think it would make sense to nuke another message in btf_get_prog_ctx_type ?
> With this newly gained usability of global function the message
> "arg#0 type is not a struct"
> is not useful.
> It was marginally useful in the past. Because global funcs supported
> ptr_to_ctx only it wasn't seen as often.
> Now this message probably can simply be removed. wdyt?
Yes, I hit this log message while was working on the patch and it
looked confusing but forgot to adjust/remove it.
I will prepare patch.
Thank you.
--
Dmitrii Banshchikov
