From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5D30C43381 for ; Mon, 18 Mar 2019 02:53:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7481B20857 for ; Mon, 18 Mar 2019 02:53:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727740AbfCRCx6 (ORCPT ); Sun, 17 Mar 2019 22:53:58 -0400 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:42304 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727682AbfCRCx5 (ORCPT ); Sun, 17 Mar 2019 22:53:57 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 6318727ACE; Sun, 17 Mar 2019 22:53:51 -0400 (EDT) Date: Mon, 18 Mar 2019 13:53:51 +1100 (AEDT) From: Finn Thain To: Geert Uytterhoeven cc: Andreas Schwab , kbuild test robot , kbuild-all@01.org, linux-m68k , Arnd Bergmann , Linux Kernel Mailing List Subject: Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7] In-Reply-To: Message-ID: References: <201903042049.npxcZzps%fengguang.wu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 Mar 2019, I wrote: > ... I did another experiment with the latter (forced inline) approach, > to see if some optimizations can still be used with -ffreestanding. > > diff --git a/include/linux/string.h b/include/linux/string.h > index 7927b875f80c..25b5bf689018 100644 > --- a/include/linux/string.h > +++ b/include/linux/string.h > @@ -436,6 +436,58 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) > return p; > } > > +#else > + > +//__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) > +//{ > +// return __builtin_strncpy(p, q, size); > +//} > + > +__FORTIFY_INLINE char *strcat(char *p, const char *q) > +{ > + return __builtin_strcat(p, q); > +} > + > +__FORTIFY_INLINE __kernel_size_t strlen(const char *p) > +{ > + return __builtin_strlen(p); > +} > + > +__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) > +{ > + return __builtin_strncat(p, q, count); > +} > + > +__FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) > +{ > + return __builtin_memset(p, c, size); > +} > + > +//__FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) > +//{ > +// return __builtin_memcpy(p, q, size); > +//} > + > +__FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) > +{ > + return __builtin_memmove(p, q, size); > +} > + > +__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) > +{ > + return __builtin_memcmp(p, q, size); > +} > + > +__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) > +{ > + return __builtin_memchr(p, c, size); > +} > + > +__FORTIFY_INLINE char *strcpy(char *p, const char *q) > +{ > + return __builtin_strcpy(p, q); > +} > + > #endif > > /** > > > The result of this patch really is confusing. It still suppresses the > warning you raised: > > arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming > offset 8 is out of the bounds [0, 7] [-Warray-bounds] > #define memcpy(d, s, n) __builtin_memcpy(d, s, n) > ^~~~~~~~~~~~~~~~~~~~~~~~~ > include/linux/string.h:456:3: note: in expansion of macro 'memcpy' > memcpy(dest, src, dest_len); > ^~~~~~ > > But it also causes new ones, because of __builtin_memset(): > > drivers/video/fbdev/core/fbcvt.c: In function 'fb_find_mode_cvt': > drivers/video/fbdev/core/fbcvt.c:312:16: warning: 'cvt.flags' may be used uninit ialized in this function [-Wmaybe-uninitialized] > cvt.flags |= FB_CVT_FLAG_MARGINS; > ^~ > > Apparently the compiler doesn't understand that __builtin_memset() has > the effect of initialization. Weird. > The other weird thing is that this warning doesn't show up when CONFIG_FORTIFY_SOURCE=y, even though the technique is much the same, that is, __builtin_memset() gets wrapped in a static inline memset() function. Anyway, a quick and dirty microbenchmark under qemu-m68k shows that this patch reduces system time for 'time find / -false' by approx. 10%. Interestingly, the -ffreestanding option doesn't make much difference to this particular microbenchmark. --