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 11276C4332F for ; Fri, 4 Mar 2022 05:04:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235384AbiCDFFc (ORCPT ); Fri, 4 Mar 2022 00:05:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230244AbiCDFF3 (ORCPT ); Fri, 4 Mar 2022 00:05:29 -0500 Received: from conssluserg-06.nifty.com (conssluserg-06.nifty.com [210.131.2.91]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C80EF15DB20; Thu, 3 Mar 2022 21:04:41 -0800 (PST) Received: from mail-pg1-f172.google.com (mail-pg1-f172.google.com [209.85.215.172]) (authenticated) by conssluserg-06.nifty.com with ESMTP id 22454SmI025698; Fri, 4 Mar 2022 14:04:28 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-06.nifty.com 22454SmI025698 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1646370268; bh=jTwouyxM3J2bGsjkif3hrT7Ur9j36OcaWK3XsK/Pf0g=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=HZxyqhpvaaGXOMstMeva4g11sJkk1mM3kc78uyYDTKsDQmtHrpszVU67fkMdh6NEm K0e3zELCn9CjXEY0Lud5PWS+wnU/3cIvqE6NdsDqEogGAz1ej1u5+1jB+ZSVJgKhmi 3H447i87Jqj1ttE8q6Zt2W8LqjYkqIqoezh8iRv7bvSBDPybRnvSUKpoBjLFHgAmlw 4kOdGOxxhTvCt826LQmEPPkkjpXIPsNnznrc8CWTDfe1/ZcYgCzgqI83cCgRWgXZxT kzr+sBBU3Lsrzt1lKSqgovPhBWspe+eS/9cFHY5hJVBocr0t7P88o+g9JEBIKB/+vw 9aWhRM0T8+CTg== X-Nifty-SrcIP: [209.85.215.172] Received: by mail-pg1-f172.google.com with SMTP id 6so2016390pgg.0; Thu, 03 Mar 2022 21:04:28 -0800 (PST) X-Gm-Message-State: AOAM5300EnFyClbS35adIWJBR5xC//BjLUW94G5157bsPXo/XxjDUUE6 omwTzKmCmiUimdOuuDBuRgyfGSVuixBwfdJAY4M= X-Google-Smtp-Source: ABdhPJy7yEBFzg8WVxU6/sj/Ux+ZdTxFr+OJzk/reUK8ZrhDBHy/0ChWjVVKYQFgs5mGheJGY/lCU6ek25oVyKnWIys= X-Received: by 2002:a63:1d44:0:b0:373:5612:629b with SMTP id d4-20020a631d44000000b003735612629bmr33492754pgm.352.1646370267758; Thu, 03 Mar 2022 21:04:27 -0800 (PST) MIME-Version: 1.0 References: <20220301145233.3689119-1-arnd@kernel.org> In-Reply-To: From: Masahiro Yamada Date: Fri, 4 Mar 2022 14:03:50 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/3] [v3] Kbuild: move to -std=gnu11 To: Nathan Chancellor Cc: Arnd Bergmann , Arnd Bergmann , Linus Torvalds , Marco Elver , Jani Nikula , David Sterba , Alex Shi , Nick Desaulniers , Miguel Ojeda , Mark Rutland , Linux Kbuild mailing list , llvm@lists.linux.dev, "open list:DOCUMENTATION" , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 2, 2022 at 1:53 AM Nathan Chancellor wrote: > > On Tue, Mar 01, 2022 at 03:52:31PM +0100, 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 standa= rds > > 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 using gnu_inline behavior and gnu11 using standard c99+ > > behavior, 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 -Wextra, which happens with the > > 'make W=3D1' option, as well as for three drivers in the kernel that al= ways > > enable -Wextra, 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. > > > > 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-YgXUy2Jaj7pnk= dKpcovt8fYbVFW3TA@mail.gmail.com/ > > Link: https://github.com/ClangBuiltLinux/linux/issues/1603 > > Suggested-by: Linus Torvalds > > Acked-by: Marco Elver > > Acked-by: Jani Nikula > > Acked-by: David Sterba > > Reviewed-by: Alex Shi > > Reviewed-by: Nick Desaulniers > > Reviewed-by: Miguel Ojeda > > Cc: Masahiro Yamada > > Cc: Mark Rutland > > Cc: linux-kbuild@vger.kernel.org > > Cc: llvm@lists.linux.dev > > Cc: linux-doc@vger.kernel.org > > Cc: linux-kernel@vger.kernel.org > > Signed-off-by: Arnd Bergmann > > Reviewed-by: Nathan Chancellor > > One comment below. > > > --- > > [v3] > > - split out USERCFLAGS to a separate patch > > - add -Wdeclaration-after-statement patch from Mark Rutland > > - leave out C17 reference > > - more rewording the descrption > > > > [v2] > > - added -std=3Dgnu11 back, rather than just relying on the default > > - minor changes to changelog text > > --- > > Documentation/process/programming-language.rst | 6 +++--- > > .../translations/it_IT/process/programming-language.rst | 4 ++-- > > .../translations/zh_CN/process/programming-language.rst | 3 +-- > > .../translations/zh_TW/process/programming-language.rst | 3 +-- > > Makefile | 4 ++-- > > 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, 15 insertions(+), 13 deletions(-) > > > > diff --git a/Documentation/process/programming-language.rst b/Documenta= tion/process/programming-language.rst > > index ec474a70a02f..5fc9160ca1fa 100644 > > --- a/Documentation/process/programming-language.rst > > +++ b/Documentation/process/programming-language.rst > > @@ -5,9 +5,9 @@ Programming Language > > > > 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 IS= O C90 > > -(including some C99 features). ``clang`` [clang]_ is also supported, s= ee > > -docs on :ref:`Building Linux with Clang/LLVM `. > > +under ``-std=3Dgnu11`` [gcc-c-dialect-options]_: the GNU dialect of IS= O C11. > > +``clang`` [clang]_ is also supported, see docs on > > +:ref:`Building Linux with Clang/LLVM `. > > > > This dialect contains many extensions to the language [gnu-extensions]= _, > > and many of them are used within the kernel as a matter of course. > > diff --git a/Documentation/translations/it_IT/process/programming-langu= age.rst b/Documentation/translations/it_IT/process/programming-language.rst > > index 41db2598ce11..c1a9b481a6f9 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 > > > > Il kernel =C3=A8 scritto nel linguaggio di programmazione C [it-c-lang= uage]_. > > Pi=C3=B9 precisamente, il kernel viene compilato con ``gcc`` [it-gcc]_= usando > > -l'opzione ``-std=3Dgnu89`` [it-gcc-c-dialect-options]_: il dialetto GN= U > > -dello standard ISO C90 (con l'aggiunta di alcune funzionalit=C3=A0 da = C99). > > +l'opzione ``-std=3Dgnu11`` [it-gcc-c-dialect-options]_: il dialetto GN= U > > +dello standard ISO C11. > > Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione > > :ref:`Building Linux with Clang/LLVM `. > > > > diff --git a/Documentation/translations/zh_CN/process/programming-langu= age.rst b/Documentation/translations/zh_CN/process/programming-language.rst > > index 2a47a1d2ec20..fabdc338dbfb 100644 > > --- a/Documentation/translations/zh_CN/process/programming-language.rst > > +++ b/Documentation/translations/zh_CN/process/programming-language.rst > > @@ -9,8 +9,7 @@ > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > > > =E5=86=85=E6=A0=B8=E6=98=AF=E7=94=A8C=E8=AF=AD=E8=A8=80 :ref:`c-langua= ge ` =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 = GNU =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 = GNU =E6=96=B9=E8=A8=80 > > > > =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 > > > > diff --git a/Documentation/translations/zh_TW/process/programming-langu= age.rst b/Documentation/translations/zh_TW/process/programming-language.rst > > index 54e3699eadf8..144bdaf81a41 100644 > > --- a/Documentation/translations/zh_TW/process/programming-language.rst > > +++ b/Documentation/translations/zh_TW/process/programming-language.rst > > @@ -12,8 +12,7 @@ > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > > > =E5=85=A7=E6=A0=B8=E6=98=AF=E7=94=A8C=E8=AA=9E=E8=A8=80 :ref:`c-langua= ge ` =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 = GNU =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 = GNU =E6=96=B9=E8=A8=80 > > > > =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 > > > > diff --git a/Makefile b/Makefile > > index 289ce2be8032..94fa9a849a7a 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -515,7 +515,7 @@ KBUILD_CFLAGS :=3D -Wall -Wundef -Werror=3Dstrict= -prototypes -Wno-trigraphs \ > > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PI= E \ > > -Werror=3Dimplicit-function-declaration -Werror=3Dimpl= icit-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_I= MPLICIT_FALLTHROUGH) > > > > ifdef CONFIG_CC_IS_CLANG > > KBUILD_CPPFLAGS +=3D -Qunused-arguments > > -# The kernel builds with '-std=3Dgnu89' so use of GNU extensions is ac= ceptable. > > +# The kernel builds with '-std=3Dgnu11' so use of GNU extensions is ac= ceptable. > > 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 white= listed names. > > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso= 32/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 -W= no-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/Makef= ile > > 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-variab= le) > > 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/g= reybus/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 > > This Makefile uses its own -std=3D option because it is a userland tool. > Seems like this hunk could just be dropped or the -std=3D argument could > be bumped here too? > Right, this is a userland tool. I do not mind either way. BTW, this makefile is somewhat corrupted because ../greybus_protocols.h does not exist. (but it is working, relying on the built-in rules) If Arnd does not mind sending v4, maybe we can split this into two paches: 1/4 : add -Wno-shift-negative-value where -Wextra is used 2/4 : Kbuild: move to -std=3Dgnu11 1/4 adds -Wno-shift-negative-value whether it is the kernel space or user-land. -- Best Regards Masahiro Yamada