linux-kernel - Re: [PATCH v2 3/5] Revert "lib/string.c: implement a basic bcmp"

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Message-ID: <20200820033419.GC2167124@ubuntu-n2-xlarge-x86>
Date:   Wed, 19 Aug 2020 20:34:19 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Joe Perches <joe@...ches.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Axtens <dja@...ens.net>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Yury Norov <yury.norov@...il.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Bruce Ashfield <bruce.ashfield@...il.com>,
        Marco Elver <elver@...gle.com>,
        Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>,
        Andi Kleen <ak@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>
Subject: Re: [PATCH v2 3/5] Revert "lib/string.c: implement a basic bcmp"

On Wed, Aug 19, 2020 at 12:16:52PM -0700, Nick Desaulniers wrote:
> This reverts commit 5f074f3e192f10c9fade898b9b3b8812e3d83342.
> 
> An earlier commit in the series prevents the compiler from emitting
> calls to bcmp as part of "libcall optimization," and there are no
> explicit callers, so we can now safely remove this interface.
> 
> Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  include/linux/string.h |  3 ---
>  lib/string.c           | 20 --------------------
>  2 files changed, 23 deletions(-)
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
> index b1f3894a0a3e..f3bdb74bc230 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -155,9 +155,6 @@ extern void * memscan(void *,int,__kernel_size_t);
>  #ifndef __HAVE_ARCH_MEMCMP
>  extern int memcmp(const void *,const void *,__kernel_size_t);
>  #endif
> -#ifndef __HAVE_ARCH_BCMP
> -extern int bcmp(const void *,const void *,__kernel_size_t);
> -#endif
>  #ifndef __HAVE_ARCH_MEMCHR
>  extern void * memchr(const void *,int,__kernel_size_t);
>  #endif
> diff --git a/lib/string.c b/lib/string.c
> index 6012c385fb31..69328b8353e1 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -922,26 +922,6 @@ __visible int memcmp(const void *cs, const void *ct, size_t count)
>  EXPORT_SYMBOL(memcmp);
>  #endif
>  
> -#ifndef __HAVE_ARCH_BCMP
> -/**
> - * bcmp - returns 0 if and only if the buffers have identical contents.
> - * @a: pointer to first buffer.
> - * @b: pointer to second buffer.
> - * @len: size of buffers.
> - *
> - * The sign or magnitude of a non-zero return value has no particular
> - * meaning, and architectures may implement their own more efficient bcmp(). So
> - * while this particular implementation is a simple (tail) call to memcmp, do
> - * not rely on anything but whether the return value is zero or non-zero.
> - */
> -#undef bcmp
> -int bcmp(const void *a, const void *b, size_t len)
> -{
> -	return memcmp(a, b, len);
> -}
> -EXPORT_SYMBOL(bcmp);
> -#endif
> -
>  #ifndef __HAVE_ARCH_MEMSCAN
>  /**
>   * memscan - Find a character in an area of memory.
> -- 
> 2.28.0.297.g1956fa8f8d-goog
>