From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6EE8B53A4; Mon, 28 Feb 2022 11:25:59 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B4E1D1FB; Mon, 28 Feb 2022 03:25:53 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.20.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 736C33F73D; Mon, 28 Feb 2022 03:25:50 -0800 (PST) Date: Mon, 28 Feb 2022 11:25:36 +0000 From: Mark Rutland To: Arnd Bergmann Cc: linux-kbuild@vger.kernel.org, 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, Marco Elver Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11 Message-ID: References: <20220228103142.3301082-1-arnd@kernel.org> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220228103142.3301082-1-arnd@kernel.org> Hi Arnd, This is great! On Mon, Feb 28, 2022 at 11:27:43AM +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 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=gnu11 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=1' option, as well as for three drivers in the kernel that always > 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. > > Nathan Chancellor reported an additional -Wdeclaration-after-statement > warning that appears in a system header on arm, this still needs a > workaround. FWIW, I had a go at moving to c99 a few weeks ago (to be able to use for-loop-declarations in some concurrency primitives), and when I tried, I also saw declaration-after-statement warnings when building modpost.c, which is easy enough to fix: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=treewide/gnu99&id=505775bd6fd0bc1883f3271f826963066bbdc194 Thanks, Mark. > 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@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=gnu11 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/Documentation/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 > > The kernel is written in the C programming language [c-language]_. > More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ > -under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90 > -(including some C99 features). ``clang`` [clang]_ is also supported, see > +under ``-std=gnu11`` [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 `. > > This dialect contains many extensions to the language [gnu-extensions]_, > diff --git a/Documentation/translations/it_IT/process/programming-language.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 > > Il kernel è scritto nel linguaggio di programmazione C [it-c-language]_. > Più precisamente, il kernel viene compilato con ``gcc`` [it-gcc]_ usando > -l'opzione ``-std=gnu89`` [it-gcc-c-dialect-options]_: il dialetto GNU > -dello standard ISO C90 (con l'aggiunta di alcune funzionalità da C99). > +l'opzione ``-std=gnu11`` [it-gcc-c-dialect-options]_: il dialetto GNU > +dello standard ISO C11 (con l'aggiunta di alcune funzionalità da C17). > Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione > :ref:`Building Linux with Clang/LLVM `. > > diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@ > ============ > > 内核是用C语言 :ref:`c-language ` 编写的。更准确地说，内核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 这种方言包含对语言 :ref:`gnu-extensions ` 的许多扩展，当然，它们许多都在内核中使用。 > > diff --git a/Documentation/translations/zh_TW/process/programming-language.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 @@ > ============ > > 內核是用C語言 :ref:`c-language ` 編寫的。更準確地說，內核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 這種方言包含對語言 :ref:`gnu-extensions ` 的許多擴展，當然，它們許多都在內核中使用。 > > diff --git a/Makefile b/Makefile > index 289ce2be8032..66496eaeb9ec 100644 > --- a/Makefile > +++ b/Makefile > @@ -432,7 +432,7 @@ HOSTCXX = g++ > endif > > export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \ > - -O2 -fomit-frame-pointer -std=gnu89 > + -O2 -fomit-frame-pointer -std=gnu11 > export KBUILD_USERLDFLAGS := > > KBUILD_HOSTCFLAGS := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS) > @@ -515,7 +515,7 @@ KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ > -Werror=implicit-function-declaration -Werror=implicit-int \ > -Werror=return-type -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > KBUILD_CPPFLAGS := -D__KERNEL__ > KBUILD_AFLAGS_KERNEL := > KBUILD_CFLAGS_KERNEL := > @@ -782,7 +782,7 @@ KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) > > ifdef CONFIG_CC_IS_CLANG > KBUILD_CPPFLAGS += -Qunused-arguments > -# The kernel builds with '-std=gnu89' so use of GNU extensions is acceptable. > +# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. > KBUILD_CFLAGS += -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 whitelisted 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 += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common \ > -Werror-implicit-function-declaration \ > -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > VDSO_CFLAGS += -O2 > # Some useful compiler-dependent flags from top-level Makefile > VDSO_CFLAGS += $(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 += -Wno-unused-parameter > subdir-ccflags-y += -Wno-type-limits > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > +subdir-ccflags-y += -Wno-shift-negative-value > subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable) > subdir-ccflags-y += $(call cc-disable-warning, frame-address) > subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror > diff --git a/drivers/staging/greybus/tools/Makefile b/drivers/staging/greybus/tools/Makefile > index ad0ae8053b79..a3bbd73171f2 100644 > --- a/drivers/staging/greybus/tools/Makefile > +++ b/drivers/staging/greybus/tools/Makefile > @@ -12,7 +12,8 @@ CFLAGS += -std=gnu99 -Wall -Wextra -g \ > -Wredundant-decls \ > -Wcast-align \ > -Wsign-compare \ > - -Wno-missing-field-initializers > + -Wno-missing-field-initializers \ > + -Wno-shift-negative-value > > CC := $(CROSS_COMPILE)gcc > > 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 += $(condflags) > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > subdir-ccflags-y += -Wno-type-limits > +subdir-ccflags-y += -Wno-shift-negative-value > > obj-$(CONFIG_BTRFS_FS) := btrfs.o > > 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 += $(call cc-option, -Wstringop-truncation) > KBUILD_CFLAGS += -Wno-missing-field-initializers > KBUILD_CFLAGS += -Wno-sign-compare > KBUILD_CFLAGS += -Wno-type-limits > +KBUILD_CFLAGS += -Wno-shift-negative-value > > KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 > > -- > 2.29.2 > 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3D573C433EF for ; Mon, 28 Feb 2022 11:25:56 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 3BC2110E4C9; Mon, 28 Feb 2022 11:25:55 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id 3CBF310E389; Mon, 28 Feb 2022 11:25:54 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B4E1D1FB; Mon, 28 Feb 2022 03:25:53 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.20.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 736C33F73D; Mon, 28 Feb 2022 03:25:50 -0800 (PST) Date: Mon, 28 Feb 2022 11:25:36 +0000 From: Mark Rutland To: Arnd Bergmann Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11 Message-ID: References: <20220228103142.3301082-1-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220228103142.3301082-1-arnd@kernel.org> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, Marco Elver , Michal Marek , linux-doc@vger.kernel.org, Arnd Bergmann , Jonathan Corbet , linux-staging@lists.linux.dev, Masahiro Yamada , llvm@lists.linux.dev, Nick Desaulniers , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, greybus-dev@lists.linaro.org, Alex Shi , Federico Vaga , Hu Haowen , intel-gfx@lists.freedesktop.org, linux-btrfs@vger.kernel.org, Linus Torvalds , linux-doc-tw-discuss@lists.sourceforge.net, linux-kbuild@vger.kernel.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Arnd, This is great! On Mon, Feb 28, 2022 at 11:27:43AM +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 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=gnu11 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=1' option, as well as for three drivers in the kernel that always > 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. > > Nathan Chancellor reported an additional -Wdeclaration-after-statement > warning that appears in a system header on arm, this still needs a > workaround. FWIW, I had a go at moving to c99 a few weeks ago (to be able to use for-loop-declarations in some concurrency primitives), and when I tried, I also saw declaration-after-statement warnings when building modpost.c, which is easy enough to fix: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=treewide/gnu99&id=505775bd6fd0bc1883f3271f826963066bbdc194 Thanks, Mark. > 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@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=gnu11 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/Documentation/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 > > The kernel is written in the C programming language [c-language]_. > More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ > -under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90 > -(including some C99 features). ``clang`` [clang]_ is also supported, see > +under ``-std=gnu11`` [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 `. > > This dialect contains many extensions to the language [gnu-extensions]_, > diff --git a/Documentation/translations/it_IT/process/programming-language.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 > > Il kernel è scritto nel linguaggio di programmazione C [it-c-language]_. > Più precisamente, il kernel viene compilato con ``gcc`` [it-gcc]_ usando > -l'opzione ``-std=gnu89`` [it-gcc-c-dialect-options]_: il dialetto GNU > -dello standard ISO C90 (con l'aggiunta di alcune funzionalità da C99). > +l'opzione ``-std=gnu11`` [it-gcc-c-dialect-options]_: il dialetto GNU > +dello standard ISO C11 (con l'aggiunta di alcune funzionalità da C17). > Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione > :ref:`Building Linux with Clang/LLVM `. > > diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@ > ============ > > 内核是用C语言 :ref:`c-language ` 编写的。更准确地说，内核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 这种方言包含对语言 :ref:`gnu-extensions ` 的许多扩展，当然，它们许多都在内核中使用。 > > diff --git a/Documentation/translations/zh_TW/process/programming-language.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 @@ > ============ > > 內核是用C語言 :ref:`c-language ` 編寫的。更準確地說，內核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 這種方言包含對語言 :ref:`gnu-extensions ` 的許多擴展，當然，它們許多都在內核中使用。 > > diff --git a/Makefile b/Makefile > index 289ce2be8032..66496eaeb9ec 100644 > --- a/Makefile > +++ b/Makefile > @@ -432,7 +432,7 @@ HOSTCXX = g++ > endif > > export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \ > - -O2 -fomit-frame-pointer -std=gnu89 > + -O2 -fomit-frame-pointer -std=gnu11 > export KBUILD_USERLDFLAGS := > > KBUILD_HOSTCFLAGS := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS) > @@ -515,7 +515,7 @@ KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ > -Werror=implicit-function-declaration -Werror=implicit-int \ > -Werror=return-type -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > KBUILD_CPPFLAGS := -D__KERNEL__ > KBUILD_AFLAGS_KERNEL := > KBUILD_CFLAGS_KERNEL := > @@ -782,7 +782,7 @@ KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) > > ifdef CONFIG_CC_IS_CLANG > KBUILD_CPPFLAGS += -Qunused-arguments > -# The kernel builds with '-std=gnu89' so use of GNU extensions is acceptable. > +# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. > KBUILD_CFLAGS += -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 whitelisted 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 += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common \ > -Werror-implicit-function-declaration \ > -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > VDSO_CFLAGS += -O2 > # Some useful compiler-dependent flags from top-level Makefile > VDSO_CFLAGS += $(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 += -Wno-unused-parameter > subdir-ccflags-y += -Wno-type-limits > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > +subdir-ccflags-y += -Wno-shift-negative-value > subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable) > subdir-ccflags-y += $(call cc-disable-warning, frame-address) > subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror > diff --git a/drivers/staging/greybus/tools/Makefile b/drivers/staging/greybus/tools/Makefile > index ad0ae8053b79..a3bbd73171f2 100644 > --- a/drivers/staging/greybus/tools/Makefile > +++ b/drivers/staging/greybus/tools/Makefile > @@ -12,7 +12,8 @@ CFLAGS += -std=gnu99 -Wall -Wextra -g \ > -Wredundant-decls \ > -Wcast-align \ > -Wsign-compare \ > - -Wno-missing-field-initializers > + -Wno-missing-field-initializers \ > + -Wno-shift-negative-value > > CC := $(CROSS_COMPILE)gcc > > 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 += $(condflags) > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > subdir-ccflags-y += -Wno-type-limits > +subdir-ccflags-y += -Wno-shift-negative-value > > obj-$(CONFIG_BTRFS_FS) := btrfs.o > > 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 += $(call cc-option, -Wstringop-truncation) > KBUILD_CFLAGS += -Wno-missing-field-initializers > KBUILD_CFLAGS += -Wno-sign-compare > KBUILD_CFLAGS += -Wno-type-limits > +KBUILD_CFLAGS += -Wno-shift-negative-value > > KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 > > -- > 2.29.2 > 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 111A5C433F5 for ; Mon, 28 Feb 2022 12:08:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: 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linux-btrfs@vger.kernel.org, Marco Elver Subject: Re: [PATCH] [v2] Kbuild: move to -std=gnu11 Message-ID: References: <20220228103142.3301082-1-arnd@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220228103142.3301082-1-arnd@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220228_032556_930479_54469214 X-CRM114-Status: GOOD ( 36.71 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org SGkgQXJuZCwKClRoaXMgaXMgZ3JlYXQhCgpPbiBNb24sIEZlYiAyOCwgMjAyMiBhdCAxMToyNzo0 M0FNICswMTAwLCBBcm5kIEJlcmdtYW5uIHdyb3RlOgo+IEZyb206IEFybmQgQmVyZ21hbm4gPGFy 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Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 89D5210E832; Mon, 28 Feb 2022 14:26:08 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id 3CBF310E389; Mon, 28 Feb 2022 11:25:54 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B4E1D1FB; Mon, 28 Feb 2022 03:25:53 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.20.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 736C33F73D; Mon, 28 Feb 2022 03:25:50 -0800 (PST) Date: Mon, 28 Feb 2022 11:25:36 +0000 From: Mark Rutland To: Arnd Bergmann Message-ID: References: <20220228103142.3301082-1-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220228103142.3301082-1-arnd@kernel.org> X-Mailman-Approved-At: Mon, 28 Feb 2022 14:26:05 +0000 Subject: Re: [Intel-gfx] [PATCH] [v2] Kbuild: move to -std=gnu11 X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, Marco Elver , Michal Marek , linux-doc@vger.kernel.org, Arnd Bergmann , Jonathan Corbet , linux-staging@lists.linux.dev, Masahiro Yamada , llvm@lists.linux.dev, Nick Desaulniers , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, greybus-dev@lists.linaro.org, Alex Shi , Federico Vaga , Hu Haowen , intel-gfx@lists.freedesktop.org, linux-btrfs@vger.kernel.org, Linus Torvalds , linux-doc-tw-discuss@lists.sourceforge.net, linux-kbuild@vger.kernel.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Hi Arnd, This is great! On Mon, Feb 28, 2022 at 11:27:43AM +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 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=gnu11 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=1' option, as well as for three drivers in the kernel that always > 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. > > Nathan Chancellor reported an additional -Wdeclaration-after-statement > warning that appears in a system header on arm, this still needs a > workaround. FWIW, I had a go at moving to c99 a few weeks ago (to be able to use for-loop-declarations in some concurrency primitives), and when I tried, I also saw declaration-after-statement warnings when building modpost.c, which is easy enough to fix: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=treewide/gnu99&id=505775bd6fd0bc1883f3271f826963066bbdc194 Thanks, Mark. > 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@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=gnu11 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/Documentation/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 > > The kernel is written in the C programming language [c-language]_. > More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ > -under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90 > -(including some C99 features). ``clang`` [clang]_ is also supported, see > +under ``-std=gnu11`` [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 `. > > This dialect contains many extensions to the language [gnu-extensions]_, > diff --git a/Documentation/translations/it_IT/process/programming-language.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 > > Il kernel è scritto nel linguaggio di programmazione C [it-c-language]_. > Più precisamente, il kernel viene compilato con ``gcc`` [it-gcc]_ usando > -l'opzione ``-std=gnu89`` [it-gcc-c-dialect-options]_: il dialetto GNU > -dello standard ISO C90 (con l'aggiunta di alcune funzionalità da C99). > +l'opzione ``-std=gnu11`` [it-gcc-c-dialect-options]_: il dialetto GNU > +dello standard ISO C11 (con l'aggiunta di alcune funzionalità da C17). > Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione > :ref:`Building Linux with Clang/LLVM `. > > diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@ > ============ > > 内核是用C语言 :ref:`c-language ` 编写的。更准确地说，内核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下编译的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 这种方言包含对语言 :ref:`gnu-extensions ` 的许多扩展，当然，它们许多都在内核中使用。 > > diff --git a/Documentation/translations/zh_TW/process/programming-language.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 @@ > ============ > > 內核是用C語言 :ref:`c-language ` 編寫的。更準確地說，內核通常是用 :ref:`gcc ` > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C90的 GNU 方言（ > -包括一些C99特性） > +在 ``-std=gnu11`` :ref:`gcc-c-dialect-options ` 下編譯的：ISO C11的 GNU 方言（ > +包括一些C17特性） > > 這種方言包含對語言 :ref:`gnu-extensions ` 的許多擴展，當然，它們許多都在內核中使用。 > > diff --git a/Makefile b/Makefile > index 289ce2be8032..66496eaeb9ec 100644 > --- a/Makefile > +++ b/Makefile > @@ -432,7 +432,7 @@ HOSTCXX = g++ > endif > > export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \ > - -O2 -fomit-frame-pointer -std=gnu89 > + -O2 -fomit-frame-pointer -std=gnu11 > export KBUILD_USERLDFLAGS := > > KBUILD_HOSTCFLAGS := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS) > @@ -515,7 +515,7 @@ KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ > -Werror=implicit-function-declaration -Werror=implicit-int \ > -Werror=return-type -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > KBUILD_CPPFLAGS := -D__KERNEL__ > KBUILD_AFLAGS_KERNEL := > KBUILD_CFLAGS_KERNEL := > @@ -782,7 +782,7 @@ KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) > > ifdef CONFIG_CC_IS_CLANG > KBUILD_CPPFLAGS += -Qunused-arguments > -# The kernel builds with '-std=gnu89' so use of GNU extensions is acceptable. > +# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. > KBUILD_CFLAGS += -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 whitelisted 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 += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \ > -fno-strict-aliasing -fno-common \ > -Werror-implicit-function-declaration \ > -Wno-format-security \ > - -std=gnu89 > + -std=gnu11 > VDSO_CFLAGS += -O2 > # Some useful compiler-dependent flags from top-level Makefile > VDSO_CFLAGS += $(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 += -Wno-unused-parameter > subdir-ccflags-y += -Wno-type-limits > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > +subdir-ccflags-y += -Wno-shift-negative-value > subdir-ccflags-y += $(call cc-disable-warning, unused-but-set-variable) > subdir-ccflags-y += $(call cc-disable-warning, frame-address) > subdir-ccflags-$(CONFIG_DRM_I915_WERROR) += -Werror > diff --git a/drivers/staging/greybus/tools/Makefile b/drivers/staging/greybus/tools/Makefile > index ad0ae8053b79..a3bbd73171f2 100644 > --- a/drivers/staging/greybus/tools/Makefile > +++ b/drivers/staging/greybus/tools/Makefile > @@ -12,7 +12,8 @@ CFLAGS += -std=gnu99 -Wall -Wextra -g \ > -Wredundant-decls \ > -Wcast-align \ > -Wsign-compare \ > - -Wno-missing-field-initializers > + -Wno-missing-field-initializers \ > + -Wno-shift-negative-value > > CC := $(CROSS_COMPILE)gcc > > 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 += $(condflags) > subdir-ccflags-y += -Wno-missing-field-initializers > subdir-ccflags-y += -Wno-sign-compare > subdir-ccflags-y += -Wno-type-limits > +subdir-ccflags-y += -Wno-shift-negative-value > > obj-$(CONFIG_BTRFS_FS) := btrfs.o > > 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 += $(call cc-option, -Wstringop-truncation) > KBUILD_CFLAGS += -Wno-missing-field-initializers > KBUILD_CFLAGS += -Wno-sign-compare > KBUILD_CFLAGS += -Wno-type-limits > +KBUILD_CFLAGS += -Wno-shift-negative-value > > KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 > > -- > 2.29.2 >