linux-kernel - Re: [PATCH 1/1] arch:hexagon/powerpc: use KSYM_NAME

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Message-ID: <CANiq72=K1sXz=TjBSjx+7JuTueH6vjbz9--Q2dGDYj3naKvroQ@mail.gmail.com>
Date:   Sun, 18 Jun 2023 16:20:14 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     maninder1.s@...sung.com, Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "bcain@...cinc.com" <bcain@...cinc.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
        "nathanl@...ux.ibm.com" <nathanl@...ux.ibm.com>,
        "ustavoars@...nel.org" <ustavoars@...nel.org>,
        "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
        "gary@...yguo.net" <gary@...yguo.net>,
        "ojeda@...nel.org" <ojeda@...nel.org>,
        "pmladek@...e.com" <pmladek@...e.com>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Onkarnath <onkarnath.1@...sung.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>
Subject: Re: [PATCH 1/1] arch:hexagon/powerpc: use KSYM_NAME_LEN in array size

On Wed, May 31, 2023 at 1:14 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, May 29, 2023 at 04:50:45PM +0200, Miguel Ojeda wrote:
> > Kees: what is the current stance on `[static N]` parameters? Something like:
> >
> >     const char *kallsyms_lookup(unsigned long addr,
> >                                 unsigned long *symbolsize,
> >                                 unsigned long *offset,
> >     -                           char **modname, char *namebuf);
> >     +                           char **modname, char namebuf[static KSYM_NAME_LEN]);
> >
> > makes the compiler complain about cases like these (even if trivial):
> >
> >     arch/powerpc/xmon/xmon.c:1711:10: error: array argument is too small;
> >         contains 128 elements, callee requires at least 512
> > [-Werror,-Warray-bounds]
> >             name = kallsyms_lookup(pc, &size, &offset, NULL, tmpstr);
> >                  ^                                           ~~~~~~
> >     ./include/linux/kallsyms.h:86:29: note: callee declares array
> > parameter as static here
> >             char **modname, char namebuf[static KSYM_NAME_LEN]);
> >                                  ^      ~~~~~~~~~~~~~~~~~~~~~~
>
> Wouldn't that be a good thing? (I.e. complain about the size mismatch?)

Yeah, I would say so (i.e. I meant it as a good thing).

> > But I only see 2 files in the kernel using `[static N]` (from 2020 and
> > 2021). Should something else be used instead (e.g. `__counted_by`),
> > even if constexpr-sized?.
>
> Yeah, it seems pretty uncommon. I'd say traditionally arrays aren't
> based too often, rather structs containing them.
>
> But ultimately, yeah, everything could gain __counted_by and friends in
> the future.

That would be nice!

Cheers,
Miguel