BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Dmitrii Banshchikov <me@ubique.spb.ru>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, kafai@fb.com, songliubraving@fb.com,
	yhs@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org,
	rdna@fb.com
Subject: Re: [PATCH v3 bpf-next 3/4] bpf: Support pointers in global func args
Date: Fri, 12 Feb 2021 18:09:37 -0800
Message-ID: <20210213020937.g6lt3pczqbjj5h2u@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210212205642.620788-4-me@ubique.spb.ru>

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?

  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12 20:56 [PATCH v3 bpf-next 0/4] Add support of pointer to struct in global functions Dmitrii Banshchikov
2021-02-12 20:56 ` [PATCH v3 bpf-next 1/4] bpf: Rename bpf_reg_state variables Dmitrii Banshchikov
2021-02-12 21:11   ` Andrii Nakryiko
2021-02-12 20:56 ` [PATCH v3 bpf-next 2/4] bpf: Extract nullable reg type conversion into a helper function Dmitrii Banshchikov
2021-02-12 21:12   ` Andrii Nakryiko
2021-02-12 20:56 ` [PATCH v3 bpf-next 3/4] bpf: Support pointers in global func args Dmitrii Banshchikov
2021-02-12 21:14   ` Andrii Nakryiko
2021-02-13  2:09   ` Alexei Starovoitov [this message]
2021-02-15  6:25     ` Dmitrii Banshchikov
2021-02-12 20:56 ` [PATCH v3 bpf-next 4/4] selftests/bpf: Add unit tests for pointers in global functions Dmitrii Banshchikov
2021-02-12 21:15   ` Andrii Nakryiko
2021-02-23  6:43   ` Andrii Nakryiko
2021-02-23  8:22     ` [PATCH] selftests/bpf: Fix a compiler warning in global func test Dmitrii Banshchikov
2021-02-24 15:50       ` patchwork-bot+netdevbpf

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210213020937.g6lt3pczqbjj5h2u@ast-mbp.dhcp.thefacebook.com \
    --to=alexei.starovoitov@gmail.com \
    --cc=andrii@kernel.org \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=john.fastabend@gmail.com \
    --cc=kafai@fb.com \
    --cc=kpsingh@chromium.org \
    --cc=me@ubique.spb.ru \
    --cc=rdna@fb.com \
    --cc=songliubraving@fb.com \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git