diff mbox series

[1/3,v3] Kbuild: move to -std=gnu11

Message ID 20220301145233.3689119-1-arnd@kernel.org (mailing list archive)
State New
Headers show
Series [1/3,v3] Kbuild: move to -std=gnu11 | expand

Commit Message

Arnd Bergmann March 1, 2022, 2:52 p.m. UTC
From: Arnd Bergmann <arnd@arndb.de>

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 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=1' option, as well as for three drivers in the kernel that always
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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
Link: https://github.com/ClangBuiltLinux/linux/issues/1603
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Marco Elver <elver@google.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: David Sterba <dsterba@suse.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
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 <arnd@arndb.de>
---
[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=gnu11 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(-)

Comments

Nathan Chancellor March 1, 2022, 4:53 p.m. UTC | #1
On Tue, Mar 01, 2022 at 03:52:31PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> 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 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=1' option, as well as for three drivers in the kernel that always
> 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Acked-by: Marco Elver <elver@google.com>
> Acked-by: Jani Nikula <jani.nikula@intel.com>
> Acked-by: David Sterba <dsterba@suse.com>
> Reviewed-by: Alex Shi <alexs@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> 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 <arnd@arndb.de>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

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=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> -(including some C99 features). ``clang`` [clang]_ is also supported, see
> -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> +``clang`` [clang]_ is also supported, see docs on
> +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
>  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
>  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
>  
> diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
>  ============
>  
>  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
>  
>  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> --- a/Documentation/translations/zh_TW/process/programming-language.rst
> +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> @@ -12,8 +12,7 @@
>  ============
>  
>  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
>  
>  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -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

This Makefile uses its own -std= option because it is a userland tool.
Seems like this hunk could just be dropped or the -std= argument could
be bumped here too?

>  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
> 
>
Masahiro Yamada March 4, 2022, 5:03 a.m. UTC | #2
On Wed, Mar 2, 2022 at 1:53 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Tue, Mar 01, 2022 at 03:52:31PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > 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 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=1' option, as well as for three drivers in the kernel that always
> > 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > Acked-by: Marco Elver <elver@google.com>
> > Acked-by: Jani Nikula <jani.nikula@intel.com>
> > Acked-by: David Sterba <dsterba@suse.com>
> > Reviewed-by: Alex Shi <alexs@kernel.org>
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > 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 <arnd@arndb.de>
>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
>
> 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=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> > -(including some C99 features). ``clang`` [clang]_ is also supported, see
> > -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> > +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> > +``clang`` [clang]_ is also supported, see docs on
> > +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
> >  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
> >  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> >
> > diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
> >  ============
> >
> >  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
> >
> >  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> > --- a/Documentation/translations/zh_TW/process/programming-language.rst
> > +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> > @@ -12,8 +12,7 @@
> >  ============
> >
> >  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
> >
> >  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -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
>
> This Makefile uses its own -std= option because it is a userland tool.
> Seems like this hunk could just be dropped or the -std= 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=gnu11




1/4 adds -Wno-shift-negative-value
whether it is the kernel space or user-land.





--
Best Regards
Masahiro Yamada
Sedat Dilek March 4, 2022, 11:24 a.m. UTC | #3
On Wed, Mar 2, 2022 at 5:29 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> 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 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=1' option, as well as for three drivers in the kernel that always
> 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Acked-by: Marco Elver <elver@google.com>
> Acked-by: Jani Nikula <jani.nikula@intel.com>
> Acked-by: David Sterba <dsterba@suse.com>
> Reviewed-by: Alex Shi <alexs@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> 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 <arnd@arndb.de>
> ---
> [v3]
>  - split out USERCFLAGS to a separate patch
>  - add -Wdeclaration-after-statement patch from Mark Rutland
>  - leave out C17 reference
>  - more rewording the descrption
>

I was able to build and boot on bare metal.

No new warnings in my build-log here after switching to -std=gnu11.

Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v13.0.0 x86-64

- sed@ -

> [v2]
>  - added -std=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> -(including some C99 features). ``clang`` [clang]_ is also supported, see
> -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> +``clang`` [clang]_ is also supported, see docs on
> +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
>  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
>  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
>
> diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
>  ============
>
>  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
>
>  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> --- a/Documentation/translations/zh_TW/process/programming-language.rst
> +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> @@ -12,8 +12,7 @@
>  ============
>
>  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
>
>  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -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
>
Sedat Dilek March 4, 2022, 11:37 a.m. UTC | #4
On Wed, Mar 2, 2022 at 5:29 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> 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 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=1' option, as well as for three drivers in the kernel that always
> 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Acked-by: Marco Elver <elver@google.com>
> Acked-by: Jani Nikula <jani.nikula@intel.com>
> Acked-by: David Sterba <dsterba@suse.com>
> Reviewed-by: Alex Shi <alexs@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> 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 <arnd@arndb.de>
> ---

Arnd, please CC me on further patches/patchsets.
Thanks.

- Sedat -

> [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=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> -(including some C99 features). ``clang`` [clang]_ is also supported, see
> -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> +``clang`` [clang]_ is also supported, see docs on
> +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
>  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
>  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
>
> diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
>  ============
>
>  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
>
>  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> --- a/Documentation/translations/zh_TW/process/programming-language.rst
> +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> @@ -12,8 +12,7 @@
>  ============
>
>  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
>
>  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -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
>
Sedat Dilek March 4, 2022, 4:25 p.m. UTC | #5
On Wed, Mar 2, 2022 at 5:29 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> 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 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=1' option, as well as for three drivers in the kernel that always
> 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Acked-by: Marco Elver <elver@google.com>
> Acked-by: Jani Nikula <jani.nikula@intel.com>
> Acked-by: David Sterba <dsterba@suse.com>
> Reviewed-by: Alex Shi <alexs@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> 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 <arnd@arndb.de>

When I saw the first patches in this area, I was thinking what about
the tools/ build-system?
This ECO system has its own rules.

I use CONFIG_DEBUG_INFO_BTF=y in my kernels which means
tools/bpf/resolve_btfids will be built.
This uses hardcoded -std=gnu89.

$ git grep 'std=gnu89' tools/
tools/lib/bpf/Makefile:override CFLAGS += -std=gnu89
tools/testing/selftests/sync/Makefile:CFLAGS += -O2 -g -std=gnu89
-pthread -Wall -Wextra

Furthermore, we have several places using C99 which can be replaced by C11 now.

$ git grep 'std=gnu99' tools/ | wc -l
20

We already have C11 in tools/:

$ git grep 'std=gnu11' tools/
tools/testing/selftests/wireguard/qemu/Makefile:        $(MUSL_CC) -o
$@ $(CFLAGS) $(LDFLAGS) -std=gnu11 $<

What about having a central place where we define the
STD_GNU_C_VERSION (as a suggestion)?
This might be helpful for people dealing with diverse C version standards.

Also with STD_GNU_CXX_VERSION which is used AFAICS only in tools/:

$ git grep 'std=gnu++' tools/
tools/build/feature/Makefile:   $(BUILDXX) -std=gnu++11
tools/build/feature/Makefile:   $(BUILDXX) -std=gnu++14
                 \
tools/build/feature/Makefile:   $(BUILDXX) -std=gnu++14
                 \
tools/build/feature/Makefile:   $(BUILDXX) -std=gnu++14
                 \
tools/perf/Makefile.config:CXXFLAGS += -std=gnu++14 -fno-exceptions -fno-rtti

Looks like one place should be -std=gnu++14.
( I had no deeper look. No testing. )

Just some thoughts.

- Sedat -

> ---
> [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=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> -(including some C99 features). ``clang`` [clang]_ is also supported, see
> -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> +``clang`` [clang]_ is also supported, see docs on
> +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
>  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
>  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
>
> diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
>  ============
>
>  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
>
>  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> --- a/Documentation/translations/zh_TW/process/programming-language.rst
> +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> @@ -12,8 +12,7 @@
>  ============
>
>  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
>
>  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -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
>
Sedat Dilek March 6, 2022, 10:01 a.m. UTC | #6
On Fri, Mar 4, 2022 at 12:24 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Wed, Mar 2, 2022 at 5:29 PM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > 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 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=1' option, as well as for three drivers in the kernel that always
> > 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-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1603
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > Acked-by: Marco Elver <elver@google.com>
> > Acked-by: Jani Nikula <jani.nikula@intel.com>
> > Acked-by: David Sterba <dsterba@suse.com>
> > Reviewed-by: Alex Shi <alexs@kernel.org>
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > 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 <arnd@arndb.de>
> > ---
> > [v3]
> >  - split out USERCFLAGS to a separate patch
> >  - add -Wdeclaration-after-statement patch from Mark Rutland
> >  - leave out C17 reference
> >  - more rewording the descrption
> >
>
> I was able to build and boot on bare metal.
>
> No new warnings in my build-log here after switching to -std=gnu11.
>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v13.0.0 x86-64
>

I have re-tested with Debian's LLVM/Clang v14.0.0-rc2.

Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v14.0.0-rc2 (x86-64)

- sed@ -

> - sed@ -
>
> > [v2]
> >  - added -std=gnu11 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/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
> > -(including some C99 features). ``clang`` [clang]_ is also supported, see
> > -docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> > +under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
> > +``clang`` [clang]_ is also supported, see docs on
> > +:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
> >  Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
> >  :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> >
> > diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@
> >  ============
> >
> >  内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
> > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
> >
> >  这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
> > --- a/Documentation/translations/zh_TW/process/programming-language.rst
> > +++ b/Documentation/translations/zh_TW/process/programming-language.rst
> > @@ -12,8 +12,7 @@
> >  ============
> >
> >  內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
> > -在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
> >
> >  這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -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
> >
Sedat Dilek March 6, 2022, 3:31 p.m. UTC | #7
On Fri, Mar 4, 2022 at 5:25 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
[ ... ]
> When I saw the first patches in this area, I was thinking what about
> the tools/ build-system?
> This ECO system has its own rules.
>

My other goal was to build perf with my selfmade or distro LLVM/Clang
and -std=gnu11.

I was able to do so:

$ git log --oneline --no-merges v5.17-rc6..for-5.17/tools-std_gnu11-dileks-v2
2d99b1cfa897 (for-5.17/tools-std_gnu11-dileks-v2) perf: Use -std=gnu11
c345a183c4ef tools: libtraceevent: Use -std=gnu11
26f77082f233 tools: libsubcmd: Use -std=gnu11
aaba58ec81c8 tools: libbpf: Use -std=gnu11
ffc800af3be4 tools: libapi: Use -std=gnu11

For perf/libperl-support I needed an extra patch:

$ git log --oneline --no-merges
v5.17-rc6..for-5.17/perf-libperl_support-clang-dileks
316a1917ec05 (for-5.17/perf-libperl_support-clang-dileks) perf: Fix
libperl support with clang and perl v5.34

For details see [1].

I can send the patches if someone wants them.

[1] https://marc.info/?t=164646683300002&r=1&w=2
diff mbox series

Patch

diff --git a/Documentation/process/programming-language.rst b/Documentation/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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
-(including some C99 features). ``clang`` [clang]_ is also supported, see
-docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
+under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
+``clang`` [clang]_ is also supported, see docs on
+:ref:`Building Linux with Clang/LLVM <kbuild_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-language.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 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.
 Linux supporta anche ``clang`` [it-clang]_, leggete la documentazione
 :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
 
diff --git a/Documentation/translations/zh_CN/process/programming-language.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 @@ 
 ============
 
 内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说,内核通常是用 :ref:`gcc <cn_gcc>`
-在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <cn_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 <cn_gcc-c-dialect-options>` 下编译的:ISO C11的 GNU 方言
 
 这种方言包含对语言 :ref:`gnu-extensions <cn_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..144bdaf81a41 100644
--- a/Documentation/translations/zh_TW/process/programming-language.rst
+++ b/Documentation/translations/zh_TW/process/programming-language.rst
@@ -12,8 +12,7 @@ 
 ============
 
 內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說,內核通常是用 :ref:`gcc <tw_gcc>`
-在 ``-std=gnu89`` :ref:`gcc-c-dialect-options <tw_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 <tw_gcc-c-dialect-options>` 下編譯的:ISO C11的 GNU 方言
 
 這種方言包含對語言 :ref:`gnu-extensions <tw_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..94fa9a849a7a 100644
--- a/Makefile
+++ b/Makefile
@@ -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