Messages in this thread |  | | Date | Sun, 27 Feb 2022 17:04:50 -0600 | Subject | Re: [greybus-dev] [PATCH] Kbuild: remove -std=gnu89 from compiler arguments | From | Alex Elder <> |
| |
On 2/27/22 3:52 PM, 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 and gnu89, but this was taken care of by defining 'inline' to > include __attribute__((gnu_inline)) in order to allow building with > clang a while ago. > > One minor issue that remains is an added gcc warning for shifts of > negative integers when building with -Werror, which happens with the > 'make W=1' option, as well as for three drivers in the kernel that always > enable -Werror, but it was only observed with the i915 driver so far. > > Nathan Chancellor reported an additional -Wdeclaration-after-statement > warning that appears in a system header on arm, this still needs a > workaround. > > Since the differences between gnu99, gnu11 and gnu17 are fairly minimal > and mainly impact warnings at the -Wpedantic level that the kernel > never enables, the easiest way is to just leave out the -std=gnu89 > argument entirely, and rely on the compiler default language setting, > which is gnu11 for gcc-5, and gnu1x/gnu17 for all other supported > versions of gcc or clang. > > 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> > Cc: Masahiro Yamada <masahiroy@kernel.org> > Cc: linux-kbuild@vger.kernel.org > Cc: llvm@lists.linux.dev > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > I put the suggestion into patch form, based on what we discussed > in the thread. I only gave it minimal testing, but it would > be good to have it in linux-next if we want to do this in the > merge window.
Did you determine what needed the new compiler flag based on compilation results?
Glancing at the Greybus code, I don't believe there's any reason it needs to shift a negative value. Such warnings could be fixed by making certain variables unsigned, for example.
I have no objection, I'll just make a note of it.
-Alex
> --- > Documentation/process/programming-language.rst | 4 ++-- > .../translations/it_IT/process/programming-language.rst | 4 ++-- > .../translations/zh_CN/process/programming-language.rst | 4 ++-- > .../translations/zh_TW/process/programming-language.rst | 4 ++-- > Makefile | 7 +++---- > arch/arm64/kernel/vdso32/Makefile | 3 +-- > drivers/gpu/drm/i915/Makefile | 1 + > drivers/staging/greybus/tools/Makefile | 3 ++- > fs/btrfs/Makefile | 1 + > scripts/Makefile.extrawarn | 1 + > 10 files changed, 17 insertions(+), 15 deletions(-) >
. . .
> 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 >
. . .
|  |