linux-kernel - Re: [PATCH 2/3] treewide: use -Wdeclaration-after-statement

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Date:   Tue, 1 Mar 2022 12:06:02 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        Jani Nikula <jani.nikula@...el.com>,
        David Sterba <dsterba@...e.com>, Alex Shi <alexs@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] treewide: use -Wdeclaration-after-statement

On Tue, Mar 1, 2022 at 11:57 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Tue, Mar 1, 2022 at 6:52 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > From: Mark Rutland <mark.rutland@....com>
> >
> > In a subsequent patch we'll move the kernel from using `-std=gnu89` to
> > `-std=gnu11`, permitting the use of additional C11 features such as
> > for-loop initial declarations.
> >
> > One contentious aspect of C99 is that it permits mixed declarations and
> > code, and for now at least, it seems preferable to enforce that
> > declarations must come first.
> >
> > These warnings were already disabled in the kernel itself, but not
> > for KBUILD_USERCFLAGS or the compat VDSO on arch/arm64, which uses
> > a separate set of CFLAGS.
> >
> > This patch fixes an existing violation in modpost.c, which is not
> > reported because of the missing flag in KBUILD_USERCFLAGS:
> >
> > | scripts/mod/modpost.c: In function ‘match’:
> > | scripts/mod/modpost.c:837:3: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
> > |   837 |   const char *endp = p + strlen(p) - 1;
> > |       |   ^~~~~
> >
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > [arnd: don't add a duplicate flag to the default set, update changelog]
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> Thanks for the patches!
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

That said, there's a few additional places that reset KBUILD_CFLAGS.
$ git grep -rn "KBUILD_CFLAGS :=" | grep -v filter-out | grep -v subst
arch/mips/boot/compressed/Makefile:30:KBUILD_CFLAGS :=
$(KBUILD_CFLAGS) -D__KERNEL__ -D__DISABLE_EXPORTS \
arch/mips/vdso/Makefile:115:$(obj-vdso): KBUILD_CFLAGS :=
$(cflags-vdso) $(native-abi)
arch/mips/vdso/Makefile:144:$(obj-vdso-o32): KBUILD_CFLAGS :=
$(cflags-vdso) -mabi=32
arch/mips/vdso/Makefile:184:$(obj-vdso-n32): KBUILD_CFLAGS :=
$(cflags-vdso) -mabi=n32
arch/parisc/boot/compressed/Makefile:17:KBUILD_CFLAGS := -D__KERNEL__
-O2 -DBOOTLOADER
arch/s390/boot/Makefile:13:KBUILD_CFLAGS := $(KBUILD_CFLAGS_DECOMPRESSOR)
arch/s390/boot/compressed/Makefile:23:KBUILD_CFLAGS :=
$(KBUILD_CFLAGS_DECOMPRESSOR)
arch/s390/purgatory/Makefile:24:KBUILD_CFLAGS := -fno-strict-aliasing
-Wall -Wstrict-prototypes
arch/x86/boot/compressed/Makefile:35:KBUILD_CFLAGS := -m$(BITS) -O2
$(CLANG_FLAGS)

The parisc, s390, and x86 cases look like true positives to me (mips
looks fine FWICT).  I didn't want to nack the patch for being
incomplete, but it's not necessarily treewide.


>
> > ---
> >  Makefile                          | 3 ++-
> >  arch/arm64/kernel/vdso32/Makefile | 1 +
> >  scripts/mod/modpost.c             | 4 +++-
> >  3 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 94fa9a849a7a..37ef6a555dcd 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -432,7 +432,8 @@ HOSTCXX     = g++
> >  endif
> >
> >  export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> > -                             -O2 -fomit-frame-pointer -std=gnu89
> > +                           -O2 -fomit-frame-pointer -std=gnu89 \
> > +                           -Wdeclaration-after-statement
> >  export KBUILD_USERLDFLAGS :=
> >
> >  KBUILD_HOSTCFLAGS   := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
> > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> > index 9378ea055bf2..ed181bedbffc 100644
> > --- a/arch/arm64/kernel/vdso32/Makefile
> > +++ b/arch/arm64/kernel/vdso32/Makefile
> > @@ -68,6 +68,7 @@ VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
> >                 -fno-strict-aliasing -fno-common \
> >                 -Werror-implicit-function-declaration \
> >                 -Wno-format-security \
> > +               -Wdeclaration-after-statement \
> >                 -std=gnu11
> >  VDSO_CFLAGS  += -O2
> >  # Some useful compiler-dependent flags from top-level Makefile
> > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > index 6bfa33217914..fe693304b120 100644
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -833,8 +833,10 @@ static int match(const char *sym, const char * const pat[])
> >  {
> >         const char *p;
> >         while (*pat) {
> > +               const char *endp;
> > +
> >                 p = *pat++;
> > -               const char *endp = p + strlen(p) - 1;
> > +               endp = p + strlen(p) - 1;
> >
> >                 /* "*foo*" */
> >                 if (*p == '*' && *endp == '*') {
> > --
> > 2.29.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers