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 95959C4360C for ; Tue, 8 Oct 2019 07:45:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 354A921924 for ; Tue, 8 Oct 2019 07:45:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="RInnKvJ9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730419AbfJHHpG (ORCPT ); Tue, 8 Oct 2019 03:45:06 -0400 Received: from conssluserg-04.nifty.com ([210.131.2.83]:35946 "EHLO conssluserg-04.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730222AbfJHHpG (ORCPT ); Tue, 8 Oct 2019 03:45:06 -0400 Received: from mail-ua1-f42.google.com (mail-ua1-f42.google.com [209.85.222.42]) (authenticated) by conssluserg-04.nifty.com with ESMTP id x987ixw7010587 for ; Tue, 8 Oct 2019 16:45:00 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-04.nifty.com x987ixw7010587 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1570520701; bh=5vdyLTpEpqPrxGKiHV1GQDqsAbuwLe1TeFdRcUBrweM=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=RInnKvJ9611O6MJB6/m/3g9rYpMP2U/Uj3bFYIHKAOdXfTK+Cqhi0PNebaCSbuxiV ZMlZHPcurK7t4rsQNhSH5fncQAVVE8WmkMy6ozrCSezns+A6UMXKfpTampNuG/7PKY +giS4mAvJLtJA5KgVVvbsQdElzGwKdCm4th1cXb/IWqhPTNLH5qqC9fVSVK4Abl88h xLWZIe3bgH4goKQvKaoKAhePA1maQ/K56VuR2luqG0a4ws6KemKH34piyHlKb6fV6y JSCCOUejK+FGpMssH+8tf8wE9aVoBFp+ed+GpF1Uc4BjB5mosdVSe/t3LfH2GLTB/t BFWv015/p358w== X-Nifty-SrcIP: [209.85.222.42] Received: by mail-ua1-f42.google.com with SMTP id r25so4887660uam.3 for ; Tue, 08 Oct 2019 00:45:00 -0700 (PDT) X-Gm-Message-State: APjAAAW0mcq5B2gax2si1rLPd4nAuM0BVVXIcztBSFfvOyAdMn4B3tlx k6LMcU6z6wO8YuVb84H8WfTOEqjqMjLHOrTfSxQ= X-Google-Smtp-Source: APXvYqy6lP0GYJAxHitYgDFRxHYa2MX52vBA0gcbcApI2yNBhKsuR8rMg+UwE01vmVZNoTqdjbaL6JS3kYi86HEKnZ0= X-Received: by 2002:a9f:2213:: with SMTP id 19mr4841683uad.25.1570520699005; Tue, 08 Oct 2019 00:44:59 -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 16:44:22 +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 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. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds -- Best Regards Masahiro Yamada