[PATCH 0/6] [v3] kbuild: enable more warnings by default

[PATCH 0/6] [v3] kbuild: enable more warnings by default

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Hi Andrew,

All the warning fixes I sent for these warnings have been merged into
mainline or linux-next, so let's turn them on by default.

Since some of the bugfixes are still in flight in maintainer trees,
I have rebased this on top of the mm/mm-nonmm-unstable branch
for the purpose of merging these during the second half of the
6.10 merge window.

I did thorough testing of the changes on x86, arm64 and arm, as
well as allmodconfig testing across all architectures and compilers.
It is still likely that this will catch more warnings that show
up in configurations I did not test, or in newly merged code,
and I plan to send fixes for those as well.

I also sent patches to enable -Wunused-const-variable and
-Wtautological-constant-out-of-range-compare, but those still
need additional bugfixes to get merged first.

Arnd Bergmann (6):
  [v3] kbuild: turn on -Wextra by default
  [v3] kbuild: remove redundant extra warning flags
  [v3] kbuild: turn on -Wrestrict by default
  [v3] kbuild: enable -Wformat-truncation on clang
  [v3] kbuild: enable -Wcast-function-type-strict unconditionally
  [v3] kbuild: enable -Wstringop-truncation globally

 scripts/Makefile.extrawarn | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

-- 
2.39.2

Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Kees Cook <keescook@chromium.org>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

[PATCH 1/6] [v3] kbuild: turn on -Wextra by default

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The -Wextra option controls a number of different warnings that differ
slightly by compiler version. Some are useful in general, others are
better left at W=1 or higher. Based on earlier work, the ones that
should be disabled by default are left for the higher warning levels
already, and a lot of the useful ones have no remaining output when
enabled.

Move the -Wextra option up into the set of default-enabled warnings
and just rely on the individual ones getting disabled as needed.

The -Wunused warning was always grouped with this, so turn it on
by default as well, except for the -Wunused-parameter warning that
really has no value at all for the kernel since many interfaces
have intentionally unused arguments.

Acked-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.extrawarn | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index c5af566e911a..c247552c192c 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -82,12 +82,14 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
 # Warn if there is an enum types mismatch
 KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
 
+KBUILD_CFLAGS += -Wextra
+KBUILD_CFLAGS += -Wunused
+
 #
 # W=1 - warnings which may be relevant and do not occur too often
 #
 ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 
-KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
 KBUILD_CFLAGS += $(call cc-option, -Wrestrict)
 KBUILD_CFLAGS += -Wmissing-format-attribute
 KBUILD_CFLAGS += -Wold-style-definition
@@ -190,6 +192,7 @@ else
 
 # The following turn off the warnings enabled by -Wextra
 KBUILD_CFLAGS += -Wno-sign-compare
+KBUILD_CFLAGS += -Wno-unused-parameter
 
 endif
 
-- 
2.39.2

Re: [PATCH 1/6] [v3] kbuild: turn on -Wextra by default

[Kees Cook]

On Mon, Apr 15, 2024 at 02:20:32PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The -Wextra option controls a number of different warnings that differ
> slightly by compiler version. Some are useful in general, others are
> better left at W=1 or higher. Based on earlier work, the ones that
> should be disabled by default are left for the higher warning levels
> already, and a lot of the useful ones have no remaining output when
> enabled.
> 
> Move the -Wextra option up into the set of default-enabled warnings
> and just rely on the individual ones getting disabled as needed.
> 
> The -Wunused warning was always grouped with this, so turn it on
> by default as well, except for the -Wunused-parameter warning that
> really has no value at all for the kernel since many interfaces
> have intentionally unused arguments.
> 
> Acked-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

[PATCH 2/6] [v3] kbuild: remove redundant extra warning flags

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

There is no point in turning individual options off and then on again,
or vice versa, as the last one always wins. Now that -Wextra always
gets passed first, remove all the redundant lines about warnings
that are implied by either -Wall or -Wextra, and keep only the last
one that disables it in some configurations.

This should not have any effect but keep the Makefile more readable
and the command line shorter.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.extrawarn | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index c247552c192c..8b3f5b62b837 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -37,11 +37,6 @@ else
 KBUILD_CFLAGS += -Wno-main
 endif
 
-# These warnings generated too much noise in a regular build.
-# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
-KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
-KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
-
 # These result in bogus false positives
 KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer)
 
@@ -90,16 +85,9 @@ KBUILD_CFLAGS += -Wunused
 #
 ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
 
-KBUILD_CFLAGS += $(call cc-option, -Wrestrict)
 KBUILD_CFLAGS += -Wmissing-format-attribute
-KBUILD_CFLAGS += -Wold-style-definition
 KBUILD_CFLAGS += -Wmissing-include-dirs
-KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable)
 KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
-KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned)
-KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow)
-KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation)
-KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
 
 KBUILD_CPPFLAGS += -Wundef
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
@@ -150,9 +138,6 @@ ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
 KBUILD_CFLAGS += -Wdisabled-optimization
 KBUILD_CFLAGS += -Wshadow
 KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
-KBUILD_CFLAGS += -Wmissing-field-initializers
-KBUILD_CFLAGS += -Wtype-limits
-KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
 KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
 
 KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2
-- 
2.39.2

[PATCH 3/6] [v3] kbuild: turn on -Wrestrict by default

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

All known -Wrestrict warnings are addressed now, so don't disable the warning
any more.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.extrawarn | 1 -
 1 file changed, 1 deletion(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 8b3f5b62b837..95466a04d51b 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -98,7 +98,6 @@ else
 # Suppress them by using -Wno... except for W=1.
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
-KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
 KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
-- 
2.39.2

Re: [PATCH 3/6] [v3] kbuild: turn on -Wrestrict by default

[Kees Cook]

On Mon, Apr 15, 2024 at 02:20:34PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> All known -Wrestrict warnings are addressed now, so don't disable the warning
> any more.

Ah, great! Yes, I know Gatlin was also looking at this and doing a bunch
of builds across compiler versions to verify this was ready to do too.
Gatlin, are you able to provide a "Tested-by:" tag for this patch?

-Kees

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  scripts/Makefile.extrawarn | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 8b3f5b62b837..95466a04d51b 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -98,7 +98,6 @@ else
>  # Suppress them by using -Wno... except for W=1.
>  KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
>  KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
> -KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
>  KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
>  KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
>  KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
> -- 
> 2.39.2
> 

-- 
Kees Cook

[PATCH 4/6] [v3] kbuild: enable -Wformat-truncation on clang

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

This warning option still produces output on gcc but is now clean when
building with clang, so enable it conditionally on the compiler for now.

As far as I can tell, the remaining warnings with gcc are the result of
analysing the code more deeply across inlining, while clang only does
this within a function.

Link: https://lore.kernel.org/lkml/20240326230511.GA2796782@dev-arch.thelio-3990X/
Link: https://lore.kernel.org/linux-patches/20231002-disable-wformat-truncation-overflow-non-kprintf-v1-1-35179205c8d9@kernel.org/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.extrawarn | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 95466a04d51b..202e26e6f29f 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -100,7 +100,14 @@ KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
 KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
+ifdef CONFIG_CC_IS_GCC
 KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
+else
+# Clang checks for overflow/truncation with '%p', while GCC does not:
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
+KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
+KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
+endif
 KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
 
 KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
-- 
2.39.2

[PATCH 5/6] [v3] kbuild: enable -Wcast-function-type-strict unconditionally

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

All known function cast warnings are now addressed, so the warning can
be enabled globally to catch new ones more quickly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.extrawarn | 1 -
 1 file changed, 1 deletion(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 202e26e6f29f..1d13cecc7cc7 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -129,7 +129,6 @@ endif
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
-KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict)
 KBUILD_CFLAGS += -Wno-enum-compare-conditional
 KBUILD_CFLAGS += -Wno-enum-enum-conversion
 endif
-- 
2.39.2

Re: [PATCH 5/6] [v3] kbuild: enable -Wcast-function-type-strict unconditionally

[Kees Cook]

On Mon, Apr 15, 2024 at 02:20:36PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> All known function cast warnings are now addressed, so the warning can
> be enabled globally to catch new ones more quickly.

Also yay! :)

Reviewed-by: Kees Cook <keescook@chromium.org>

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  scripts/Makefile.extrawarn | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 202e26e6f29f..1d13cecc7cc7 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -129,7 +129,6 @@ endif
>  KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
>  KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
>  KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
> -KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict)
>  KBUILD_CFLAGS += -Wno-enum-compare-conditional
>  KBUILD_CFLAGS += -Wno-enum-enum-conversion
>  endif
> -- 
> 2.39.2
> 

-- 
Kees Cook

[PATCH 6/6] [v3] kbuild: enable -Wstringop-truncation globally

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The remaining warnings of this type have been addressed, so it can
now be enabled by default, rather than only for W=1.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v3: no changes
v2: no changes
---
 scripts/Makefile.extrawarn | 1 -
 1 file changed, 1 deletion(-)

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 1d13cecc7cc7..17c511ddf48a 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -108,7 +108,6 @@ else
 KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
 KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
 endif
-KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
 
 KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
 
-- 
2.39.2

Re: [PATCH 6/6] [v3] kbuild: enable -Wstringop-truncation globally

[Kees Cook]

On Mon, Apr 15, 2024 at 02:20:37PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The remaining warnings of this type have been addressed, so it can
> now be enabled by default, rather than only for W=1.

Yeah, I know Gustavo had been working on these too. Yay!

Reviewed-by: Kees Cook <keescook@chromium.org>

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v3: no changes
> v2: no changes
> ---
>  scripts/Makefile.extrawarn | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 1d13cecc7cc7..17c511ddf48a 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -108,7 +108,6 @@ else
>  KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
>  KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
>  endif
> -KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
>  
>  KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
>  
> -- 
> 2.39.2
> 

-- 
Kees Cook