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

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Message-Id: <20220301145233.3689119-2-arnd@kernel.org>
Date:   Tue,  1 Mar 2022 15:52:32 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     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: [PATCH 2/3] treewide: use -Wdeclaration-after-statement

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>
---
 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