netdev - RE: [PATCH RFC net-next 08/14] bpf: add eBPF verifier

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1726B207@AcuExch.aculab.com>
Date:	Wed, 2 Jul 2014 08:11:20 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Alexei Starovoitov' <ast@...mgrid.com>,
	Daniel Borkmann <dborkman@...hat.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Arnaldo Carvalho de Melo" <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	"Linux API" <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC net-next 08/14] bpf: add eBPF verifier

From: Alexei Starovoitov
...
> >> +#define _(OP) ({ int ret = OP; if (ret < 0) return ret; })
...
> >> +       _(get_map_info(env, map_id, &map));
> >
> > Nit: such macros should be removed, please.
> 
> It may surely look unconventional, but alternative is to replace
> every usage of _ macro with:
> err =
> if (err)
>   return err;
> 
> and since this macro is used 38 times, it will add ~120 unnecessary
> lines that will only make code much harder to follow.
> I tried not using macro and results were not pleasing.

The problem is that they are hidden control flow.
As such they make flow analysis harder for the casual reader.

The extra lines really shouldn't matter.

	David