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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 3E074C10F14 for ; Tue, 8 Oct 2019 07:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0BB68206BB for ; Tue, 8 Oct 2019 07:53:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="QJjAMMZA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730384AbfJHHxL (ORCPT ); Tue, 8 Oct 2019 03:53:11 -0400 Received: from conssluserg-03.nifty.com ([210.131.2.82]:22326 "EHLO conssluserg-03.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730209AbfJHHxL (ORCPT ); Tue, 8 Oct 2019 03:53:11 -0400 Received: from mail-vs1-f52.google.com (mail-vs1-f52.google.com [209.85.217.52]) (authenticated) by conssluserg-03.nifty.com with ESMTP id x987qrre013428 for ; Tue, 8 Oct 2019 16:52:54 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-03.nifty.com x987qrre013428 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1570521174; bh=jJq2iZxU15jfa5j4J1bVagqa3LMlfTABDFvYt3JyXlU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=QJjAMMZAw8He5Z+axRWP8GcROebOKKybKpAAiU8cQJ75sbaAijr2IF07Dulzpc2tt InGf7MYv8emEuLuU4nq5x68kF0ttq45eT+x/oTuDyZQyCHJ5YGUFziyDWy50hYmZUv Fd29R4hQ0Ho2OfStvqPcZUYfW9liPpk/JIstlp3oQ5zQ7/bRSV92mAWN6afexBsdSR qSJypI/yXW5a+jvbfyA1jCGvYPhNKzWWiiFDBqS81azIT+ljaG2cW7H5oi9VsJWX49 HtsnG2BtrcZLMfoXr0WVo5TVJkp/3ViGMa6mF9PTwamNYNpOfj+EE9c6VfwmIWSMIW Dnq6X/Sno2qFw== X-Nifty-SrcIP: [209.85.217.52] Received: by mail-vs1-f52.google.com with SMTP id b123so10710449vsb.5 for ; Tue, 08 Oct 2019 00:52:54 -0700 (PDT) X-Gm-Message-State: APjAAAXnftAWQUxGgZwahI9vsDVj+FAsF+fZGWj/mjkHIsmo/FDxvDwO jAKYa2byao0b81WCWu+Dik9harwuYoiIdAGUGcE= X-Google-Smtp-Source: APXvYqwNZZOGI0fInnUtTIfJn5H+8MwVqsWUJciya17oGD1wiibEb4nJMXK1Y/omb2kzheaClL2AGQ6JvzdAdpE35mM= X-Received: by 2002:a67:7c03:: with SMTP id x3mr17966035vsc.155.1570521173006; Tue, 08 Oct 2019 00:52:53 -0700 (PDT) MIME-Version: 1.0 References: <20190801230358.4193-1-rikard.falkeborn@gmail.com> <20190811184938.1796-1-rikard.falkeborn@gmail.com> <20190811184938.1796-4-rikard.falkeborn@gmail.com> In-Reply-To: From: Masahiro Yamada Date: Tue, 8 Oct 2019 16:52:17 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/3] linux/bits.h: Add compile time sanity check of GENMASK inputs To: Geert Uytterhoeven Cc: Rikard Falkeborn , Andrew Morton , Joe Perches , Johannes Berg , Linux Kernel Mailing List , Haren Myneni Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 8, 2019 at 4:44 PM Masahiro Yamada wrote: > > Hi Geert, > > On Tue, Oct 8, 2019 at 4:23 PM Geert Uytterhoeven wrote: > > > > Hi Rikard, > > > > On Sun, Aug 11, 2019 at 8:52 PM Rikard Falkeborn > > wrote: > > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit > > > as the first argument and the low bit as the second argument. Mixing > > > them will return a mask with zero bits set. > > > > > > Recent commits show getting this wrong is not uncommon, see e.g. > > > commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and > > > commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK > > > macro"). > > > > > > To prevent such mistakes from appearing again, add compile time sanity > > > checking to the arguments of GENMASK() and GENMASK_ULL(). If both > > > arguments are known at compile time, and the low bit is higher than the > > > high bit, break the build to detect the mistake immediately. > > > > > > Since GENMASK() is used in declarations, BUILD_BUG_ON_ZERO() must be > > > used instead of BUILD_BUG_ON(). > > > > > > __builtin_constant_p does not evaluate is argument, it only checks if it > > > is a constant or not at compile time, and __builtin_choose_expr does not > > > evaluate the expression that is not chosen. Therefore, GENMASK(x++, 0) > > > does only evaluate x++ once. > > > > > > Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends > > > available in assembly") made the macros in linux/bits.h available in > > > assembly. Since BUILD_BUG_OR_ZERO() is not asm compatible, disable the > > > checks if the file is included in an asm file. > > > > > > Signed-off-by: Rikard Falkeborn > > > --- > > > Changes in v3: > > > - Changed back to shorter macro argument names > > > - Remove casts and use 0 instead of UL(0) in GENMASK_INPUT_CHECK(), > > > since all results in GENMASK_INPUT_CHECK() are now ints. Update > > > commit message to reflect that. > > > > > > Changes in v2: > > > - Add comment about why inputs are not checked when used in asm file > > > - Use UL(0) instead of 0 > > > - Extract mask creation in a separate macro to improve readability > > > - Use high and low instead of h and l (part of this was extracted to a > > > separate patch) > > > - Updated commit message > > > > > > Joe Perches sent a series to fix the existing misuses of GENMASK() that > > > needs to be merged before this to avoid build failures. Currently, 5 of > > > the patches are not in Linus tree, and 2 are not in linux-next. There is > > > also a patch pending by Nathan Chancellor that also needs to be merged > > > before this patch is merged to avoid build failures. > > > > > > include/linux/bits.h | 21 +++++++++++++++++++-- > > > 1 file changed, 19 insertions(+), 2 deletions(-) > > > > > > diff --git a/include/linux/bits.h b/include/linux/bits.h > > > index 669d69441a62..4ba0fb609239 100644 > > > --- a/include/linux/bits.h > > > +++ b/include/linux/bits.h > > > @@ -18,12 +18,29 @@ > > > * position @h. For example > > > * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. > > > */ > > > -#define GENMASK(h, l) \ > > > +#ifndef __ASSEMBLY__ > > > +#include > > > +#define GENMASK_INPUT_CHECK(h, l) \ > > > + (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > > > + __builtin_constant_p((l) > (h)), (l) > (h), 0))) > > > +#else > > > +/* > > > + * BUILD_BUG_ON_ZERO is not available in h files included from asm files, > > > + * disable the input check if that is the case. > > > + */ > > > +#define GENMASK_INPUT_CHECK(h, l) 0 > > > +#endif > > > + > > > +#define __GENMASK(h, l) \ > > > (((~UL(0)) - (UL(1) << (l)) + 1) & \ > > > (~UL(0) >> (BITS_PER_LONG - 1 - (h)))) > > > +#define GENMASK(h, l) \ > > > + (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > > > > > > -#define GENMASK_ULL(h, l) \ > > > +#define __GENMASK_ULL(h, l) \ > > > (((~ULL(0)) - (ULL(1) << (l)) + 1) & \ > > > (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h)))) > > > +#define GENMASK_ULL(h, l) \ > > > + (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l)) > > > > > > #endif /* __LINUX_BITS_H */ > > > > This is now commit 0fd35cd30a2fece1 ("linux/bits.h: add compile time sanity > > check of GENMASK inputs") in next-20191008. > > > > reported the following failure in sun3_defconfig, > > which I managed to reproduce with gcc-4.6.3: > > Oh dear. > > I was able to reproduce this for gcc 4.7 or 4.8, > but I did not see any problem for gcc 4.9+ > > Perhaps, is this due to broken __builtin_choose_expr or __builtin_constant_p > for old compilers? > > > > > > > > > > > lib/842/842_compress.c: In function '__split_add_bits': > > lib/842/842_compress.c:164:25: error: first argument to > > '__builtin_choose_expr' not a constant > > lib/842/842_compress.c:164:25: error: bit-field '' > > width not an integer constant > > scripts/Makefile.build:265: recipe for target > > 'lib/842/842_compress.o' failed > > > > __split_add_bits() calls GENMASK_ULL() with a non-constant. > > However __split_add_bits() itself is called with constants only. > > Apparently gcc fails to inline __split_add_bits(). > > Adding inline or always_inline doesn't help. > > If this is broken for GCC < 4.9, we might be able to workaround it as follows: diff --git a/include/linux/bits.h b/include/linux/bits.h index 4ba0fb609239..f00417baf545 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -18,7 +18,7 @@ * position @h. For example * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. */ -#ifndef __ASSEMBLY__ +#if !defined(__ASSEMBLY__) && (!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000) #include #define GENMASK_INPUT_CHECK(h, l) \ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ -- Best Regards Masahiro Yamada