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Subject: Re: [PATCH] lib/string.c: implement stpcpy
From:   Joe Perches <joe@perches.com>
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     =?ISO-8859-1?Q?D=E1vid_Bolvansk=FD?= <david.bolvansky@gmail.com>,
        Eli Friedman <efriedma@quicinc.com>, stable@vger.kernel.org,
        Sami Tolvanen <samitolvanen@google.com>,
        Tony Luck <tony.luck@intel.com>,
        Yury Norov <yury.norov@gmail.com>,
        Daniel Axtens <dja@axtens.net>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Dan Williams <dan.j.williams@intel.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Alexandru Ardelean <alexandru.ardelean@analog.com>,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Date:   Fri, 14 Aug 2020 17:52:00 -0700
In-Reply-To: <20200815002417.1512973-1-ndesaulniers@google.com>
References: <20200815002417.1512973-1-ndesaulniers@google.com>
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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?

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 },