linux-kernel - Re: [PATCHv2 bpf-next 1/9] uprobe: Add support for session consumer

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Message-ID: <202407031330.F9016C60B@keescook>
Date: Wed, 3 Jul 2024 13:36:19 -0700
From: Kees Cook <kees@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Jiri Olsa <jolsa@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...omium.org>,
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv2 bpf-next 1/9] uprobe: Add support for session consumer

On Wed, Jul 03, 2024 at 11:31:11AM -0700, Andrii Nakryiko wrote:
> On Wed, Jul 3, 2024 at 1:10 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Tue, Jul 02, 2024 at 01:51:28PM -0700, Andrii Nakryiko wrote:
> > > > +static size_t ri_size(int sessions_cnt)
> > > > +{
> > > > +       struct return_instance *ri __maybe_unused;
> > > > +
> > > > +       return sizeof(*ri) + sessions_cnt * sizeof(ri->sessions[0]);
> > >
> > > just use struct_size()?
> >
> > Yeah, lets not. This is readable, struct_size() is not.
> 
> This hack with __maybe_unused is more readable than the standard
> struct_size() helper that was added specifically for cases like this,
> really?
> 
> I wonder if Kees agrees and whether there are any downsides to using
> struct_size()
> 
> struct_size(struct return_instance, sessions, sessions_cnt) seems
> readable enough to me, in any case.

Yes, please use struct_size_t(). This is exactly what it was designed for.

Though with only 2 instances of ri_size(), maybe just use struct_size()
directly?

Also, please annotate struct return_instance with __counted_by:

+	int			sessions_cnt;
+	struct session_consumer	sessions[] __counted_by(sessions_cnt);


-- 
Kees Cook