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

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Message-ID: <CAKwvOdn8PdK-3Xhm-JFG-=1djoPPEMcANjXarGpLUTkahJoFJw@mail.gmail.com>
Date:   Fri, 14 Aug 2020 19:00:22 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Tony Luck <tony.luck@...el.com>,
        Yury Norov <yury.norov@...il.com>,
        Daniel Axtens <dja@...ens.net>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Dan Williams <dan.j.williams@...el.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] lib/string.c: implement stpcpy

On Fri, Aug 14, 2020 at 5:52 PM Joe Perches <joe@...ches.com> wrote:
>
> On Fri, 2020-08-14 at 17:24 -0700, Nick Desaulniers wrote:
> > LLVM implemented a recent "libcall optimization" that lowers calls to
> > `sprintf(dest, "%s", str)` where the return value is used to
> > `stpcpy(dest, str) - dest`. This generally avoids the machinery involved
> > in parsing format strings.
> []
> > diff --git a/include/linux/string.h b/include/linux/string.h
> []
> > @@ -31,6 +31,9 @@ size_t strlcpy(char *, const char *, size_t);
> >  #ifndef __HAVE_ARCH_STRSCPY
> >  ssize_t strscpy(char *, const char *, size_t);
> >  #endif
> > +#ifndef __HAVE_ARCH_STPCPY
> > +extern char *stpcpy(char *__restrict, const char *__restrict__);
>
> Why use two different forms for __restrict and __restrict__?
> Any real reason to use __restrict__ at all?

Bah, sorry, I recently enabled some setting in my ~/.vimrc to help me
find my cursor better:
" highlight cursor
set cursorline
set cursorcolumn

Turns out this makes it pretty difficult to see underscores, or the
lack thereof.  Will fix up.

>
> It's used nowhere else in the kernel.
>
> $ git grep -w -P '__restrict_{0,2}'
> scripts/genksyms/keywords.c:    // According to rth, c99 defines "_Bool", __restrict", __restrict__", "restrict".  KAO
> scripts/genksyms/keywords.c:    { "__restrict__", RESTRICT_KEYW },
>
>


-- 
Thanks,
~Nick Desaulniers