diff mbox series

[v3,1/2] kbuild: refactor scripts/Makefile.extrawarn

Message ID 20190831162555.31887-1-yamada.masahiro@socionext.com (mailing list archive)
State New, archived
Headers show
Series [v3,1/2] kbuild: refactor scripts/Makefile.extrawarn | expand

Commit Message

Masahiro Yamada Aug. 31, 2019, 4:25 p.m. UTC 
Instead of the warning-[123] magic, let's accumulate compiler options
to KBUILD_CFLAGS directly as the top Makefile does. I think this makes
easier to understand what is going on in this file.

This commit slightly changes the behavior, I think all of which are OK.

[1] Currently, cc-option calls are needlessly evaluated. For example,
      warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
    needs evaluating only when W=3, but it is actually evaluated for
    W=1, W=2 as well. With this commit, only relevant cc-option calls
    will be evaluated. This is a slight optimization.

[2] Currently, unsupported level like W=4 is checked by:
      $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
    This will no longer be checked, but I do not think it is a big
    deal.

[3] Currently, 4 Clang warnings (Winitializer-overrides, Wformat,
    Wsign-compare, Wformat-zero-length) are shown by any of W=1, W=2,
    and W=3. With this commit, they will be warned only by W=1. I
    think this is a more correct behavior since each warning belongs
    to only one group.

For understanding this commit correctly:

We have 3 warning groups, W=1, W=2, and W=3. You may think W=3 has a
higher level than W=1, but they are actually independent. If you like,
you can combine them like W=13. To enable all the warnings, you can
pass W=123. It is shown by 'make help', but not noticed much. Since we
support W= combination, there should not exist intersection among the
three groups. If we enable Winitializer-overrides for W=1, we do not
need to for W=2 or W=3. This is the reason why I think the change [3]
makes sense.

The documentation says -Winitializer-overrides is enabled by default.
(https://clang.llvm.org/docs/DiagnosticsReference.html#winitializer-overrides)
We negate it by passing -Wno-initializer-overrides for the normal
build, but we do not do that for W=1. This means, W=1 effectively
enables -Winitializer-overrides by the clang's default. The same for
the other three.

Add comments in case people are confused with the code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
---

Changes in v3:
  - Added yet more comments.
    Fix grammatical mistake 'does' -> 'do'.

Changes in v2:
  - Added comments and more commit log

 scripts/Makefile.extrawarn | 106 ++++++++++++++++++++-----------------
 1 file changed, 56 insertions(+), 50 deletions(-)

Comments

Arnd Bergmann Sept. 4, 2019, 9:46 p.m. UTC | #1 
On Sat, Aug 31, 2019 at 6:26 PM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:

> +# Some diagnostics enabled by default are noisy.
> +# Suppress them by using -Wno... except for W=1.
> +
>  ifdef CONFIG_CC_IS_CLANG
>  KBUILD_CFLAGS += -Wno-initializer-overrides
>  KBUILD_CFLAGS += -Wno-format
>  KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-format-zero-length
>  endif

FWIW, I just found out I missed a bug that clang failed to warn about
because of the  -Wno-format. Apparently gcc warns only about type
mismatches that result in incompatible calling conventions (e.g.
int vs int64_t) but not smaller types (int, short) that get converted to an
int anyway. Passing -Wno-format turns both off.

      Arnd
Nathan Chancellor Sept. 4, 2019, 10:40 p.m. UTC | #2 
On Wed, Sep 04, 2019 at 11:46:45PM +0200, Arnd Bergmann wrote:
> On Sat, Aug 31, 2019 at 6:26 PM Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
> 
> > +# Some diagnostics enabled by default are noisy.
> > +# Suppress them by using -Wno... except for W=1.
> > +
> >  ifdef CONFIG_CC_IS_CLANG
> >  KBUILD_CFLAGS += -Wno-initializer-overrides
> >  KBUILD_CFLAGS += -Wno-format
> >  KBUILD_CFLAGS += -Wno-sign-compare
> >  KBUILD_CFLAGS += -Wno-format-zero-length
> >  endif
> 
> FWIW, I just found out I missed a bug that clang failed to warn about
> because of the  -Wno-format. Apparently gcc warns only about type
> mismatches that result in incompatible calling conventions (e.g.
> int vs int64_t) but not smaller types (int, short) that get converted to an
> int anyway. Passing -Wno-format turns both off.
> 
>       Arnd

Hi Arnd,

This has been fixed in clang 10.0.0 but this areas has not been updated
as nobody has sent a patch yet:

https://github.com/ClangBuiltLinux/linux/issues/378#issuecomment-524411147

Cheers,
Nathan
Arnd Bergmann Sept. 5, 2019, 8:06 a.m. UTC | #3 
On Thu, Sep 5, 2019 at 12:40 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
> On Wed, Sep 04, 2019 at 11:46:45PM +0200, Arnd Bergmann wrote:
> > On Sat, Aug 31, 2019 at 6:26 PM Masahiro Yamada
> > <yamada.masahiro@socionext.com> wrote:
> >
> > FWIW, I just found out I missed a bug that clang failed to warn about
> > because of the  -Wno-format. Apparently gcc warns only about type
> > mismatches that result in incompatible calling conventions (e.g.
> > int vs int64_t) but not smaller types (int, short) that get converted to an
> > int anyway. Passing -Wno-format turns both off.
> >
> >       Arnd
>
> Hi Arnd,
>
> This has been fixed in clang 10.0.0 but this areas has not been updated
> as nobody has sent a patch yet:
>
> https://github.com/ClangBuiltLinux/linux/issues/378#issuecomment-524411147

Ok, that's good. I see that on clang-9, the documentation also
mentions that -Wformat control -Wformat-extra-args -Wformat-invalid-specifier
-Wformat-y2k -Wformat-zero-length -Wnonnull and -Wformat-security.
We can probably turn these all on, regardless. The only warning
that produces output here is -Wformat-security, and only in a couple of
files (number of warnings per file from a few hundred randconfig builds):

   384 kernel/trace/ring_buffer_benchmark.c
    176 samples/trace_printk/trace-printk.c
    174 kernel/debug/kdb/kdb_io.c
    102 arch/x86/kernel/e820.c
     80 fs/btrfs/check-integrity.c
     67 fs/reiserfs/prints.c
     63 fs/xfs/xfs_log_recover.c
     54 fs/quota/dquot.c
     53 lib/test_printf.c
     39 sound/core/sound.c
     28 arch/x86/kernel/cpu/mce/core.c
     21 kernel/trace/preemptirq_delay_test.c
     19 sound/core/seq/seq_clientmgr.c
     17 sound/pci/hda/hda_bind.c
     16 sound/usb/mixer_quirks.c
     16 arch/x86/kernel/cpu/mce/amd.c
     15 net/smc/smc_ism.c
     12 kernel/debug/kdb/kdb_main.c
      8 net/netfilter/nf_conntrack_helper.c
      4 kernel/power/suspend_test.c
      3 sound/pci/rme32.c
      3 net/dsa/dsa.c
      2 sound/pci/rme96.c
      1 sound/soc/sof/intel/hda-codec.c
      1 sound/pci/korg1212/korg1212.c

      Arnd
Masahiro Yamada Sept. 7, 2019, 2:29 a.m. UTC | #4 
On Sun, Sep 1, 2019 at 1:26 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> Instead of the warning-[123] magic, let's accumulate compiler options
> to KBUILD_CFLAGS directly as the top Makefile does. I think this makes
> easier to understand what is going on in this file.
>
> This commit slightly changes the behavior, I think all of which are OK.
>
> [1] Currently, cc-option calls are needlessly evaluated. For example,
>       warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
>     needs evaluating only when W=3, but it is actually evaluated for
>     W=1, W=2 as well. With this commit, only relevant cc-option calls
>     will be evaluated. This is a slight optimization.
>
> [2] Currently, unsupported level like W=4 is checked by:
>       $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
>     This will no longer be checked, but I do not think it is a big
>     deal.
>
> [3] Currently, 4 Clang warnings (Winitializer-overrides, Wformat,
>     Wsign-compare, Wformat-zero-length) are shown by any of W=1, W=2,
>     and W=3. With this commit, they will be warned only by W=1. I
>     think this is a more correct behavior since each warning belongs
>     to only one group.
>
> For understanding this commit correctly:
>
> We have 3 warning groups, W=1, W=2, and W=3. You may think W=3 has a
> higher level than W=1, but they are actually independent. If you like,
> you can combine them like W=13. To enable all the warnings, you can
> pass W=123. It is shown by 'make help', but not noticed much. Since we
> support W= combination, there should not exist intersection among the
> three groups. If we enable Winitializer-overrides for W=1, we do not
> need to for W=2 or W=3. This is the reason why I think the change [3]
> makes sense.
>
> The documentation says -Winitializer-overrides is enabled by default.
> (https://clang.llvm.org/docs/DiagnosticsReference.html#winitializer-overrides)
> We negate it by passing -Wno-initializer-overrides for the normal
> build, but we do not do that for W=1. This means, W=1 effectively
> enables -Winitializer-overrides by the clang's default. The same for
> the other three.
>
> Add comments in case people are confused with the code.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> Acked-by: Nick Desaulniers <ndesaulniers@google.com>
> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> ---

Both applied to linux-kbuild.


> Changes in v3:
>   - Added yet more comments.
>     Fix grammatical mistake 'does' -> 'do'.
>
> Changes in v2:
>   - Added comments and more commit log
>
>  scripts/Makefile.extrawarn | 106 ++++++++++++++++++++-----------------
>  1 file changed, 56 insertions(+), 50 deletions(-)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index a74ce2e3c33e..d226c5fb13e2 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -1,14 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0
>  # ==========================================================================
> -#
>  # make W=... settings
>  #
> -# W=1 - warnings that may be relevant and does not occur too often
> -# W=2 - warnings that occur quite often but may still be relevant
> -# W=3 - the more obscure warnings, can most likely be ignored
> -#
> -# $(call cc-option, -W...) handles gcc -W.. options which
> -# are not supported by all versions of the compiler
> +# There are three warning groups enabled by W=1, W=2, W=3.
> +# They are independent, and can be combined like W=12 or W=123.
>  # ==========================================================================
>
>  KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
> @@ -17,58 +12,69 @@ ifeq ("$(origin W)", "command line")
>    export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
>  endif
>
> -ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
> -warning-  := $(empty)
> +#
> +# W=1 - warnings which may be relevant and do not occur too often
> +#
> +ifneq ($(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
>
> -warning-1 := -Wextra -Wunused -Wno-unused-parameter
> -warning-1 += -Wmissing-declarations
> -warning-1 += -Wmissing-format-attribute
> -warning-1 += -Wmissing-prototypes
> -warning-1 += -Wold-style-definition
> -warning-1 += -Wmissing-include-dirs
> -warning-1 += $(call cc-option, -Wunused-but-set-variable)
> -warning-1 += $(call cc-option, -Wunused-const-variable)
> -warning-1 += $(call cc-option, -Wpacked-not-aligned)
> -warning-1 += $(call cc-option, -Wstringop-truncation)
> +KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
> +KBUILD_CFLAGS += -Wmissing-declarations
> +KBUILD_CFLAGS += -Wmissing-format-attribute
> +KBUILD_CFLAGS += -Wmissing-prototypes
> +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, -Wstringop-truncation)
>  # The following turn off the warnings enabled by -Wextra
> -warning-1 += -Wno-missing-field-initializers
> -warning-1 += -Wno-sign-compare
> -
> -warning-2 += -Wcast-align
> -warning-2 += -Wdisabled-optimization
> -warning-2 += -Wnested-externs
> -warning-2 += -Wshadow
> -warning-2 += $(call cc-option, -Wlogical-op)
> -warning-2 += -Wmissing-field-initializers
> -warning-2 += -Wsign-compare
> -warning-2 += $(call cc-option, -Wmaybe-uninitialized)
> -warning-2 += $(call cc-option, -Wunused-macros)
> -
> -warning-3 := -Wbad-function-cast
> -warning-3 += -Wcast-qual
> -warning-3 += -Wconversion
> -warning-3 += -Wpacked
> -warning-3 += -Wpadded
> -warning-3 += -Wpointer-arith
> -warning-3 += -Wredundant-decls
> -warning-3 += -Wswitch-default
> -warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
> -
> -warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> -warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> -warning += $(warning-$(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
> -
> -ifeq ("$(strip $(warning))","")
> -        $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
> -endif
> +KBUILD_CFLAGS += -Wno-missing-field-initializers
> +KBUILD_CFLAGS += -Wno-sign-compare
>
> -KBUILD_CFLAGS += $(warning)
>  else
>
> +# Some diagnostics enabled by default are noisy.
> +# Suppress them by using -Wno... except for W=1.
> +
>  ifdef CONFIG_CC_IS_CLANG
>  KBUILD_CFLAGS += -Wno-initializer-overrides
>  KBUILD_CFLAGS += -Wno-format
>  KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-format-zero-length
>  endif
> +
> +endif
> +
> +#
> +# W=2 - warnings which occur quite often but may still be relevant
> +#
> +ifneq ($(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
> +
> +KBUILD_CFLAGS += -Wcast-align
> +KBUILD_CFLAGS += -Wdisabled-optimization
> +KBUILD_CFLAGS += -Wnested-externs
> +KBUILD_CFLAGS += -Wshadow
> +KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
> +KBUILD_CFLAGS += -Wmissing-field-initializers
> +KBUILD_CFLAGS += -Wsign-compare
> +KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
> +KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
> +
> +endif
> +
> +#
> +# W=3 - more obscure warnings, can most likely be ignored
> +#
> +ifneq ($(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
> +
> +KBUILD_CFLAGS += -Wbad-function-cast
> +KBUILD_CFLAGS += -Wcast-qual
> +KBUILD_CFLAGS += -Wconversion
> +KBUILD_CFLAGS += -Wpacked
> +KBUILD_CFLAGS += -Wpadded
> +KBUILD_CFLAGS += -Wpointer-arith
> +KBUILD_CFLAGS += -Wredundant-decls
> +KBUILD_CFLAGS += -Wswitch-default
> +KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
> +
>  endif
> --
> 2.17.1
>
diff mbox series

Patch

diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index a74ce2e3c33e..d226c5fb13e2 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -1,14 +1,9 @@ 
 # SPDX-License-Identifier: GPL-2.0
 # ==========================================================================
-#
 # make W=... settings
 #
-# W=1 - warnings that may be relevant and does not occur too often
-# W=2 - warnings that occur quite often but may still be relevant
-# W=3 - the more obscure warnings, can most likely be ignored
-#
-# $(call cc-option, -W...) handles gcc -W.. options which
-# are not supported by all versions of the compiler
+# There are three warning groups enabled by W=1, W=2, W=3.
+# They are independent, and can be combined like W=12 or W=123.
 # ==========================================================================
 
 KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
@@ -17,58 +12,69 @@  ifeq ("$(origin W)", "command line")
   export KBUILD_ENABLE_EXTRA_GCC_CHECKS := $(W)
 endif
 
-ifdef KBUILD_ENABLE_EXTRA_GCC_CHECKS
-warning-  := $(empty)
+#
+# W=1 - warnings which may be relevant and do not occur too often
+#
+ifneq ($(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
 
-warning-1 := -Wextra -Wunused -Wno-unused-parameter
-warning-1 += -Wmissing-declarations
-warning-1 += -Wmissing-format-attribute
-warning-1 += -Wmissing-prototypes
-warning-1 += -Wold-style-definition
-warning-1 += -Wmissing-include-dirs
-warning-1 += $(call cc-option, -Wunused-but-set-variable)
-warning-1 += $(call cc-option, -Wunused-const-variable)
-warning-1 += $(call cc-option, -Wpacked-not-aligned)
-warning-1 += $(call cc-option, -Wstringop-truncation)
+KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
+KBUILD_CFLAGS += -Wmissing-declarations
+KBUILD_CFLAGS += -Wmissing-format-attribute
+KBUILD_CFLAGS += -Wmissing-prototypes
+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, -Wstringop-truncation)
 # The following turn off the warnings enabled by -Wextra
-warning-1 += -Wno-missing-field-initializers
-warning-1 += -Wno-sign-compare
-
-warning-2 += -Wcast-align
-warning-2 += -Wdisabled-optimization
-warning-2 += -Wnested-externs
-warning-2 += -Wshadow
-warning-2 += $(call cc-option, -Wlogical-op)
-warning-2 += -Wmissing-field-initializers
-warning-2 += -Wsign-compare
-warning-2 += $(call cc-option, -Wmaybe-uninitialized)
-warning-2 += $(call cc-option, -Wunused-macros)
-
-warning-3 := -Wbad-function-cast
-warning-3 += -Wcast-qual
-warning-3 += -Wconversion
-warning-3 += -Wpacked
-warning-3 += -Wpadded
-warning-3 += -Wpointer-arith
-warning-3 += -Wredundant-decls
-warning-3 += -Wswitch-default
-warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
-
-warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
-warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
-warning += $(warning-$(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
-
-ifeq ("$(strip $(warning))","")
-        $(error W=$(KBUILD_ENABLE_EXTRA_GCC_CHECKS) is unknown)
-endif
+KBUILD_CFLAGS += -Wno-missing-field-initializers
+KBUILD_CFLAGS += -Wno-sign-compare
 
-KBUILD_CFLAGS += $(warning)
 else
 
+# Some diagnostics enabled by default are noisy.
+# Suppress them by using -Wno... except for W=1.
+
 ifdef CONFIG_CC_IS_CLANG
 KBUILD_CFLAGS += -Wno-initializer-overrides
 KBUILD_CFLAGS += -Wno-format
 KBUILD_CFLAGS += -Wno-sign-compare
 KBUILD_CFLAGS += -Wno-format-zero-length
 endif
+
+endif
+
+#
+# W=2 - warnings which occur quite often but may still be relevant
+#
+ifneq ($(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+
+KBUILD_CFLAGS += -Wcast-align
+KBUILD_CFLAGS += -Wdisabled-optimization
+KBUILD_CFLAGS += -Wnested-externs
+KBUILD_CFLAGS += -Wshadow
+KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
+KBUILD_CFLAGS += -Wmissing-field-initializers
+KBUILD_CFLAGS += -Wsign-compare
+KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
+KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
+
+endif
+
+#
+# W=3 - more obscure warnings, can most likely be ignored
+#
+ifneq ($(findstring 3, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
+
+KBUILD_CFLAGS += -Wbad-function-cast
+KBUILD_CFLAGS += -Wcast-qual
+KBUILD_CFLAGS += -Wconversion
+KBUILD_CFLAGS += -Wpacked
+KBUILD_CFLAGS += -Wpadded
+KBUILD_CFLAGS += -Wpointer-arith
+KBUILD_CFLAGS += -Wredundant-decls
+KBUILD_CFLAGS += -Wswitch-default
+KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
+
 endif