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?
