linux-kernel - Re: [PATCH v2] lib/string.c: implement stpcpy

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Date:   Mon, 17 Aug 2020 12:15:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Daniel Axtens <dja@...ens.net>, Ingo Molnar <mingo@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH v2] lib/string.c: implement stpcpy

On Mon, Aug 17, 2020 at 11:36:49AM -0700, Nick Desaulniers wrote:
> That said, this libcall optimization/transformation (sprintf->stpcpy)
> does look useful to me.  Kees, do you have thoughts on me providing
> the implementation without exposing it in a header vs using
> -fno-builtin-stpcpy?  (I would need to add the missing EXPORT_SYMBOL,
> as pointed out by 0day bot and on the github thread).  I don't care
> either way; I'd just like your input before sending a V+1.  Maybe
> better to just not implement it and never implement it?

I think I would ultimately prefer -fno-builtin-stpcpy, but for now,
sure, an implementation without a header (and a biiig comment above it
detailing why and a reference to the bug) would be fine by me.

-- 
Kees Cook