Re: [PATCH v3 bpf-next 3/4] bpf: Support pointers in global func args
From: Alexei Starovoitov <hidden>
Date: 2021-02-13 02:10:28
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.
quoted hunk ↗ jump to hunk
@@ -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.
quoted hunk ↗ jump to hunk
/* 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?