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

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Date:   Fri, 4 Mar 2022 12:29:20 +0100
From:   Sedat Dilek <sedat.dilek@...il.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>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        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 4:59 PM 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>

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@...il.com> # LLVM/Clang v13.0.0 x86-64

- sed@ -

> ---
>  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
>