Kbuild: use -Wdeclaration-after-statement

The kernel is moving 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 enabled 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@arm.com>
[arnd: don't add a duplicate flag to the default set, update changelog]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v13.0.0 (x86-64)
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

diff --git a/Makefile b/Makefile
index 51e142f..84a2de3 100644 (file)
--- 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 6c01b63..f46457f 100644 (file)
--- 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=gnu89
 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 6bfa332..fe69330 100644 (file)
--- 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 == '*') {