Re: [PATCH 1/2] introduce "banned function" list

From: Jeff King <peff@peff.net>
Date: Jul 19, 2018, 21:27 UTC
Message-ID: <20180719212700.GA13151@sigill.intra.peff.net>
In-Reply-To: <CAPig+cSErDoZ5XFjfJsqfEKZ6PSKfOos=9HW-7FDXU1XEtuktA@mail.gmail.com>

On Thu, Jul 19, 2018 at 05:11:15PM -0400, Eric Sunshine wrote:

Show 21 quoted lines

> On Thu, Jul 19, 2018 at 4:39 PM Jeff King <peff@peff.net> wrote:
> > [...]
> > Let's start by banning strcpy() and sprintf(). It's not
> > impossible to use these correctly, but it's easy to do so
> > incorrectly, and there's always a better option.
> > [...]
> > Signed-off-by: Jeff King <peff@peff.net>
> > ---
> > diff --git a/banned.h b/banned.h
> > @@ -0,0 +1,19 @@
> > +/*
> > + * This header lists functions that have been banned from our code base,
> > + * because they're too easy to misuse (and even if used correctly,
> > + * complicate audits). Including this header turns them into compile-time
> > + * errors.
> > + */
> 
> When the above talks about "including this header", the implication is
> that it must be included _after_ the system header(s) which declare
> the banned functions. I wonder if that requirement should be stated
> here explicitly.

Hmm, does it need to be? I had originally intended it to be included before, actually, though in the end I put it later.

I guess it would yield declarations like strcpy_is_banned(), which would cause _different_ errors (probably link-time ones).

> (Probably not worth a re-roll.)

Yeah, I doubt it matters much either way, since the inclusion is done automatically in git-compat-util.h.

I had also originally imagined this to be triggered via DEVELOPER=1, with something like "-include banned.h" in CFLAGS. But I think it probably is appropriate for everybody to run it, since it shouldn't cause any false positives or other compilation issues.

The one I brainstormed (but forgot to mention) is that it might be possible for a platform to have strcpy as a macro already? In which case we'd need to #undef it or risk a compilation error (even if the macro isn't actually used).

-Peff