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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9829CC4332F for ; Mon, 28 Feb 2022 12:37:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233321AbiB1Mhu (ORCPT ); Mon, 28 Feb 2022 07:37:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232709AbiB1Mht (ORCPT ); Mon, 28 Feb 2022 07:37:49 -0500 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE04C7561E; Mon, 28 Feb 2022 04:37:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1646051830; x=1677587830; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version:content-transfer-encoding; bh=7B5xXQQ6ggh1HFTcP+YadDpRzLVifOjGsC04RK4u89s=; b=A4lQ+1CImVjLXftMmQh/11uPXiQgNtCt2N5R6mgtOPjEijFwjk8KayzH EyeBMWigj+9hoAKbqgnL9rfbrHgWlTwmAonL7OagbAoJFY63T46sIzQp9 ts5os4t6+uDwLz07vuEBbbjgLsIaUNozwqRV7baANCxvMRXzIdrK/0mzW r7OBydBAyMPfeyj+XFSYODzrUe+QC6xk4090ao0cW/SZlMNnyHbdpYXjh 66Z8NmSrIKDj9Eg35u3wNLMLSpZOGjJLrEZC9KnFbKmr84Q5p6brpCO2M WOsPoy62RBXvtGNBjY4eV7kZH2LqRHoZUyChLtYg11CpqsWeGr77HoLNn Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10271"; a="251703491" X-IronPort-AV: E=Sophos;i="5.90,142,1643702400"; d="scan'208";a="251703491" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Feb 2022 04:37:10 -0800 X-IronPort-AV: E=Sophos;i="5.90,142,1643702400"; d="scan'208";a="550218755" Received: from gkapusti-mobl.ccr.corp.intel.com (HELO localhost) ([10.252.51.8]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Feb 2022 04:37:04 -0800 From: Jani Nikula To: Arnd Bergmann , linux-kbuild@vger.kernel.org Cc: Arnd Bergmann , Linus Torvalds , Masahiro Yamada , llvm@lists.linux.dev, Jonathan Corbet , Federico Vaga , Alex Shi , Hu Haowen , Michal Marek , Nick Desaulniers , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc-tw-discuss@lists.sourceforge.net, linux-arm-kernel@lists.infradead.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev, linux-btrfs@vger.kernel.org Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11 In-Reply-To: <20220228103142.3301082-1-arnd@kernel.org> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20220228103142.3301082-1-arnd@kernel.org> Date: Mon, 28 Feb 2022 14:36:52 +0200 Message-ID: <87v8wz5frv.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, 28 Feb 2022, Arnd Bergmann wrote: > From: Arnd Bergmann > > During a patch discussion, Linus brought up the option of changing > the C standard version from gnu89 to gnu99, which allows using variable > declaration inside of a for() loop. While the C99, C11 and later standards > introduce many other features, most of these are already available in > gnu89 as GNU extensions as well. > > An earlier attempt to do this when gcc-5 started defaulting to > -std=3Dgnu11 failed because at the time that caused warnings about > designated initializers with older compilers. Now that gcc-5.1 is the > minimum compiler version used for building kernels, that is no longer a > concern. Similarly, the behavior of 'inline' functions changes between > gnu89 and gnu11, but this was taken care of by defining 'inline' to > include __attribute__((gnu_inline)) in order to allow building with > clang a while ago. > > One minor issue that remains is an added gcc warning for shifts of > negative integers when building with -Werror, which happens with the > 'make W=3D1' option, as well as for three drivers in the kernel that alwa= ys > enable -Werror, but it was only observed with the i915 driver so far. > To be on the safe side, add -Wno-shift-negative-value to any -Wextra > in a Makefile. Do you mean always enable -Wall and/or -Wextra instead of -Werror? We do use -Werror for our CI and development too, but it's hidden behind a config option that depends on COMPILE_TEST=3Dn to avoid any problems with allmodconfig/allyesconfig. For the future, makes me wonder if we couldn't have a way for drivers to locally enable -Wall/-Wextra in a way that incorporates the exceptions from kbuild instead of having to duplicate them. Anyway, for the i915 changes, Acked-by: Jani Nikula > > Nathan Chancellor reported an additional -Wdeclaration-after-statement > warning that appears in a system header on arm, this still needs a > workaround. > > The differences between gnu99, gnu11, gnu1x and gnu17 are fairly > minimal and mainly impact warnings at the -Wpedantic level that the > kernel never enables. Between these, gnu11 is the newest version > that is supported by all supported compiler versions, though it is > only the default on gcc-5, while all other supported versions of > gcc or clang default to gnu1x/gnu17. > > Link: https://lore.kernel.org/lkml/CAHk-=3DwiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdK= pcovt8fYbVFW3TA@mail.gmail.com/ > Link: https://github.com/ClangBuiltLinux/linux/issues/1603 > Suggested-by: Linus Torvalds > Cc: Masahiro Yamada > Cc: linux-kbuild@vger.kernel.org > Cc: llvm@lists.linux.dev > Signed-off-by: Arnd Bergmann > --- > [v2] > - added -std=3Dgnu11 back, rather than just relying on the default > - minor changes to changelog text > --- > Documentation/process/programming-language.rst | 4 ++-- > .../translations/it_IT/process/programming-language.rst | 4 ++-- > .../translations/zh_CN/process/programming-language.rst | 4 ++-- > .../translations/zh_TW/process/programming-language.rst | 4 ++-- > Makefile | 6 +++--- > arch/arm64/kernel/vdso32/Makefile | 2 +- > drivers/gpu/drm/i915/Makefile | 1 + > drivers/staging/greybus/tools/Makefile | 3 ++- > fs/btrfs/Makefile | 1 + > scripts/Makefile.extrawarn | 1 + > 10 files changed, 17 insertions(+), 13 deletions(-) > > diff --git a/Documentation/process/programming-language.rst b/Documentati= on/process/programming-language.rst > index ec474a70a02f..894f2a6eb9db 100644 > --- a/Documentation/process/programming-language.rst > +++ b/Documentation/process/programming-language.rst > @@ -5,8 +5,8 @@ Programming Language >=20=20 > The kernel is written in the C programming language [c-language]_. > More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ > -under ``-std=3Dgnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO = C90 > -(including some C99 features). ``clang`` [clang]_ is also supported, see > +under ``-std=3Dgnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO = C11 > +(including some C17 features). ``clang`` [clang]_ is also supported, see > docs on :ref:`Building Linux with Clang/LLVM `. >=20=20 > This dialect contains many extensions to the language [gnu-extensions]_, > diff --git a/Documentation/translations/it_IT/process/programming-languag= e.rst b/Documentation/translations/it_IT/process/programming-language.rst > index 41db2598ce11..aa21097737ae 100644 > --- a/Documentation/translations/it_IT/process/programming-language.rst > +++ b/Documentation/translations/it_IT/process/programming-language.rst > @@ -10,8 +10,8 @@ Linguaggio di programmazione >=20=20 > Il kernel =C3=A8 scritto nel linguaggio di programmazione C [it-c-langua= ge]_. > Pi=C3=B9 precisamente, il kernel viene compilato con ``gcc`` [it-gcc]_ u= sando > -l'opzione ``-std=3Dgnu89`` [it-gcc-c-dialect-options]_: il dialetto GNU > -dello standard ISO C90 (con l'aggiunta di alcune funzionalit=C3=A0 da C9= 9). > +l'opzione ``-std=3Dgnu11`` [it-gcc-c-dialect-options]_: il dialetto GNU > +dello standard ISO C11 (con l'aggiunta di alcune funzionalit=C3=A0 da C1= 7). > Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione > :ref:`Building Linux with Clang/LLVM `. >=20=20 > diff --git a/Documentation/translations/zh_CN/process/programming-languag= e.rst b/Documentation/translations/zh_CN/process/programming-language.rst > index 2a47a1d2ec20..58d2b3bd2d85 100644 > --- a/Documentation/translations/zh_CN/process/programming-language.rst > +++ b/Documentation/translations/zh_CN/process/programming-language.rst > @@ -9,8 +9,8 @@ > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20=20 > =E5=86=85=E6=A0=B8=E6=98=AF=E7=94=A8C=E8=AF=AD=E8=A8=80 :ref:`c-language= ` =E7=BC=96=E5=86=99=E7=9A=84=E3=80=82=E6=9B=B4=E5=87=86=E7= =A1=AE=E5=9C=B0=E8=AF=B4=EF=BC=8C=E5=86=85=E6=A0=B8=E9=80=9A=E5=B8=B8=E6=98= =AF=E7=94=A8 :ref:`gcc ` > -=E5=9C=A8 ``-std=3Dgnu89`` :ref:`gcc-c-dialect-options ` =E4=B8=8B=E7=BC=96=E8=AF=91=E7=9A=84=EF=BC=9AISO C90=E7=9A=84 GN= U =E6=96=B9=E8=A8=80=EF=BC=88 > -=E5=8C=85=E6=8B=AC=E4=B8=80=E4=BA=9BC99=E7=89=B9=E6=80=A7=EF=BC=89 > +=E5=9C=A8 ``-std=3Dgnu11`` :ref:`gcc-c-dialect-options ` =E4=B8=8B=E7=BC=96=E8=AF=91=E7=9A=84=EF=BC=9AISO C11=E7=9A=84 GN= U =E6=96=B9=E8=A8=80=EF=BC=88 > +=E5=8C=85=E6=8B=AC=E4=B8=80=E4=BA=9BC17=E7=89=B9=E6=80=A7=EF=BC=89 >=20=20 > =E8=BF=99=E7=A7=8D=E6=96=B9=E8=A8=80=E5=8C=85=E5=90=AB=E5=AF=B9=E8=AF=AD= =E8=A8=80 :ref:`gnu-extensions ` =E7=9A=84=E8=AE=B8=E5= =A4=9A=E6=89=A9=E5=B1=95=EF=BC=8C=E5=BD=93=E7=84=B6=EF=BC=8C=E5=AE=83=E4=BB= =AC=E8=AE=B8=E5=A4=9A=E9=83=BD=E5=9C=A8=E5=86=85=E6=A0=B8=E4=B8=AD=E4=BD=BF= =E7=94=A8=E3=80=82 >=20=20 > diff --git a/Documentation/translations/zh_TW/process/programming-languag= e.rst b/Documentation/translations/zh_TW/process/programming-language.rst > index 54e3699eadf8..235de05f7e2c 100644 > --- a/Documentation/translations/zh_TW/process/programming-language.rst > +++ b/Documentation/translations/zh_TW/process/programming-language.rst > @@ -12,8 +12,8 @@ > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20=20 > =E5=85=A7=E6=A0=B8=E6=98=AF=E7=94=A8C=E8=AA=9E=E8=A8=80 :ref:`c-language= ` =E7=B7=A8=E5=AF=AB=E7=9A=84=E3=80=82=E6=9B=B4=E6=BA=96=E7= =A2=BA=E5=9C=B0=E8=AA=AA=EF=BC=8C=E5=85=A7=E6=A0=B8=E9=80=9A=E5=B8=B8=E6=98= =AF=E7=94=A8 :ref:`gcc ` > -=E5=9C=A8 ``-std=3Dgnu89`` :ref:`gcc-c-dialect-options ` =E4=B8=8B=E7=B7=A8=E8=AD=AF=E7=9A=84=EF=BC=9AISO C90=E7=9A=84 GN= U =E6=96=B9=E8=A8=80=EF=BC=88 > -=E5=8C=85=E6=8B=AC=E4=B8=80=E4=BA=9BC99=E7=89=B9=E6=80=A7=EF=BC=89 > +=E5=9C=A8 ``-std=3Dgnu11`` :ref:`gcc-c-dialect-options ` =E4=B8=8B=E7=B7=A8=E8=AD=AF=E7=9A=84=EF=BC=9AISO C11=E7=9A=84 GN= U =E6=96=B9=E8=A8=80=EF=BC=88 > +=E5=8C=85=E6=8B=AC=E4=B8=80=E4=BA=9BC17=E7=89=B9=E6=80=A7=EF=BC=89 >=20=20 > =E9=80=99=E7=A8=AE=E6=96=B9=E8=A8=80=E5=8C=85=E5=90=AB=E5=B0=8D=E8=AA=9E= =E8=A8=80 :ref:`gnu-extensions ` =E7=9A=84=E8=A8=B1=E5= =A4=9A=E6=93=B4=E5=B1=95=EF=BC=8C=E7=95=B6=E7=84=B6=EF=BC=8C=E5=AE=83=E5=80= =91=E8=A8=B1=E5=A4=9A=E9=83=BD=E5=9C=A8=E5=85=A7=E6=A0=B8=E4=B8=AD=E4=BD=BF= =E7=94=A8=E3=80=82 >=20=20 > diff --git a/Makefile b/Makefile > index 289ce2be8032..66496eaeb9ec 100644 > --- a/Makefile > +++ b/Makefile > @@ -432,7 +432,7 @@ HOSTCXX =3D g++ > endif >=20=20 > export KBUILD_USERCFLAGS :=3D -Wall -Wmissing-prototypes -Wstrict-protot= ypes \ > - -O2 -fomit-frame-pointer -std=3Dgnu89 > + -O2 -fomit-frame-pointer -std=3Dgnu11 > export KBUILD_USERLDFLAGS :=3D >=20=20 > KBUILD_HOSTCFLAGS :=3D $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTC= FLAGS) > @@ -515,7 +515,7 @@ KBUILD_CFLAGS :=3D -Wall -Wundef -Werror=3Dstrict-p= rototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ > -Werror=3Dimplicit-function-declaration -Werror=3Dimplicit-int \ > -Werror=3Dreturn-type -Wno-format-security \ > - -std=3Dgnu89 > + -std=3Dgnu11 > KBUILD_CPPFLAGS :=3D -D__KERNEL__ > KBUILD_AFLAGS_KERNEL :=3D > KBUILD_CFLAGS_KERNEL :=3D > @@ -782,7 +782,7 @@ KBUILD_CFLAGS +=3D $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMP= LICIT_FALLTHROUGH) >=20=20 > ifdef CONFIG_CC_IS_CLANG > KBUILD_CPPFLAGS +=3D -Qunused-arguments > -# The kernel builds with '-std=3Dgnu89' so use of GNU extensions is acce= ptable. > +# The kernel builds with '-std=3Dgnu11' so use of GNU extensions is acce= ptable. > KBUILD_CFLAGS +=3D -Wno-gnu > # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, = as the > # source of a reference will be _MergedGlobals and not on of the whiteli= sted names. > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32= /Makefile > index 6c01b63ff56d..9378ea055bf2 100644 > --- a/arch/arm64/kernel/vdso32/Makefile > +++ b/arch/arm64/kernel/vdso32/Makefile > @@ -68,7 +68,7 @@ VDSO_CFLAGS +=3D -Wall -Wundef -Wstrict-prototypes -Wno= -trigraphs \ > -fno-strict-aliasing -fno-common \ > -Werror-implicit-function-declaration \ > -Wno-format-security \ > - -std=3Dgnu89 > + -std=3Dgnu11 > VDSO_CFLAGS +=3D -O2 > # Some useful compiler-dependent flags from top-level Makefile > VDSO_CFLAGS +=3D $(call cc32-option,-Wdeclaration-after-statement,) > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile > index 1b62b9f65196..1618a6e0af4e 100644 > --- a/drivers/gpu/drm/i915/Makefile > +++ b/drivers/gpu/drm/i915/Makefile > @@ -17,6 +17,7 @@ subdir-ccflags-y +=3D -Wno-unused-parameter > subdir-ccflags-y +=3D -Wno-type-limits > subdir-ccflags-y +=3D -Wno-missing-field-initializers > subdir-ccflags-y +=3D -Wno-sign-compare > +subdir-ccflags-y +=3D -Wno-shift-negative-value > subdir-ccflags-y +=3D $(call cc-disable-warning, unused-but-set-variable) > subdir-ccflags-y +=3D $(call cc-disable-warning, frame-address) > subdir-ccflags-$(CONFIG_DRM_I915_WERROR) +=3D -Werror > diff --git a/drivers/staging/greybus/tools/Makefile b/drivers/staging/gre= ybus/tools/Makefile > index ad0ae8053b79..a3bbd73171f2 100644 > --- a/drivers/staging/greybus/tools/Makefile > +++ b/drivers/staging/greybus/tools/Makefile > @@ -12,7 +12,8 @@ CFLAGS +=3D -std=3Dgnu99 -Wall -Wextra -g \ > -Wredundant-decls \ > -Wcast-align \ > -Wsign-compare \ > - -Wno-missing-field-initializers > + -Wno-missing-field-initializers \ > + -Wno-shift-negative-value >=20=20 > CC :=3D $(CROSS_COMPILE)gcc >=20=20 > diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile > index 4188ba3fd8c3..99f9995670ea 100644 > --- a/fs/btrfs/Makefile > +++ b/fs/btrfs/Makefile > @@ -17,6 +17,7 @@ subdir-ccflags-y +=3D $(condflags) > subdir-ccflags-y +=3D -Wno-missing-field-initializers > subdir-ccflags-y +=3D -Wno-sign-compare > subdir-ccflags-y +=3D -Wno-type-limits > +subdir-ccflags-y +=3D -Wno-shift-negative-value >=20=20 > obj-$(CONFIG_BTRFS_FS) :=3D btrfs.o >=20=20 > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn > index 8be892887d71..650d0b8ceec3 100644 > --- a/scripts/Makefile.extrawarn > +++ b/scripts/Makefile.extrawarn > @@ -36,6 +36,7 @@ KBUILD_CFLAGS +=3D $(call cc-option, -Wstringop-truncat= ion) > KBUILD_CFLAGS +=3D -Wno-missing-field-initializers > KBUILD_CFLAGS +=3D -Wno-sign-compare > KBUILD_CFLAGS +=3D -Wno-type-limits > +KBUILD_CFLAGS +=3D -Wno-shift-negative-value >=20=20 > KBUILD_CPPFLAGS +=3D -DKBUILD_EXTRA_WARN1 --=20 Jani Nikula, Intel Open Source Graphics Center