On Wed, Mar 2, 2022 at 1:53 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > On Tue, Mar 01, 2022 at 03:52:31PM +0100, Arnd Bergmann wrote: > > From: Arnd Bergmann <arnd@xxxxxxxx> > > > > 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@xxxxxxxxxxxxxx/ > > Link: https://github.com/ClangBuiltLinux/linux/issues/1603 > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Acked-by: Marco Elver <elver@xxxxxxxxxx> > > Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> > > Acked-by: David Sterba <dsterba@xxxxxxxx> > > Reviewed-by: Alex Shi <alexs@xxxxxxxxxx> > > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx> > > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > > Cc: linux-kbuild@xxxxxxxxxxxxxxx > > Cc: llvm@xxxxxxxxxxxxxxx > > Cc: linux-doc@xxxxxxxxxxxxxxx > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > > Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> > > 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
